Two wire flasher module teardown with unexpected find

[@funnlivinit]

An interesting coincidence that you would dissect this today. Just this morning I had to repair the 2 wire flasher for my 1962 Dodge Power Wagon. It uses an old school mechanical relay designed to handle up to 20 amps for multi bulb truck and trailer combinations. Instead of using a bi-metal strip, it uses a coil and gear arrangement with a tiny spring and weight. There are 2 contacts inside as well. One for the coil and one for the load. When 12 volts (possibly 6v too) is placed across the terminals the coil is energized, pulling the weight towards it and opening the coil part of the circuit while closing the load switch side. The spring then returns the gear to the start position and the cycle starts all over again. The current of the load is not really critical to the operation. However, I suspect that it would not operate properly if only 2 LEDs were used as the load. The current limit might not be enough to energize the coil sufficiently to pull the weight all the way open. Causing a fast flash, or more likely, no flash at all. Thanks for your videos! I always enjoy them. (I wish I could post a picture of it. And the part number is no longer visible.)

[@funnlivinit]

I made a quick video. kzbin.info/www/bejne/l5qun3mceteJebc

[@markhonea2461]

I can picture that by your description. Amazing the things we are capable of creating!

[@Gold63Beast]

Yeah that’s true. When I use to work for an Auto Place, I found out about these flasher relays AND that they now make relays that are compatible with vintage cars and LEDs. I use to love telling customers this “secret”. The LED relays have a much lower trigger and make it so that when/if you do buy it, paired with the right quality LED will last forever. Just have to get a quality LED bulb, that’s not too bright because it is a vintage car, a LED that is just as bright as the original and not SUPER bright that it looks aftermarket.

[@dosgos]

Send one to Big Clive for a teardown!

[@NiHaoMike64]

@@Gold63Beast If the LED is too bright, wouldn't adding a series resistor be an easy fix?

[@TinkerbatTech]

Wow. An SMD PUT? Way cool! Last I'd seen of those was 70's? Thanks for the modern/retro flasher bits...

[@MCPicoli]

Used a few in the 80s/90s in some hobby projects, as part of a relaxation oscillator. Can't remember the part number but definitely not SMD!

[@skylined5534]

I remember seeing them on Sun Micro server processor boards when I worked at Celestica in the early 2000s.

[@kimchristensen2175]

Those unijunction transistors, due to their hysteresis characteristic, were also good for squaring up sinewaves.

[@manolisgledsodakis873]

Erm, a sinewave isn't supposed to be square because then it would be a squarewave!

[@michaelclark6414]

@@manolisgledsodakis873 ffs. The idea being that you want a square wave, but you have a sinewave.

[@raygale4198]

@@manolisgledsodakis873 Squaring up the sine wave makes it much easier to measure zero crossings if you are trying to compare or phase match two waveforms.

[@michaelkaliski7651]

I built a very similar circuit from a magazine article years ago to provide variable speed delayed wipers for those drizzle days. Used a transistor follower driving a relay instead of a MOSFET but it worked well for many years.

[@IanSlothieRolfe]

I remember when UJT and PUTs were the new hotness back when I was a teenager in the 70s. Their principle benefit was that you could use them to make a single transistor oscillator that would produce a nice sounding sawtooth waveform - at a time when the cost of a normal transistor was usually about £1-3 each in today's money (less than the unijunction, but not half) and most audio oscillator or flasher circuits required 2.

[@raygale4198]

UJTs were also used to provide synced gate drive for power SCR phase control circuits in Field drive outputs of Automatic Voltage Regulators used on power generators. Basler Electric used them in almost every model AVR. The UJT was the interface between the dc control signal and the power devices.

[@LordCarpenter]

I love it when you take things to bits and provide a full analysis. Great video... as usual.

[@demef758]

A UJT? Wow! I haven't seen one of those things in probably 40 years! The first circuit I made in my college years was an oscillator based on the UJT. As I remember it, it is a PNPN stack, which makes the equivalent of a PNP + NPN latch, with the top P connection being the anode, the next N in the stack was the gate, and the bottom most N was the cathode. Once the anode got to a diode above the setting on the gate, then the latch is created and the anode is mostly shorted to the cathode. Once latched, the only way to unlatch it is to reduce the anode voltage low enough that the latch is no longer self-sustaining, after which is shuts off. It's much like a triac as I think about it except that the triac's gate is moved down to the bottom-most P connection. Ah, memories!

[@johnpossum556]

Thanks for elaborating on the details!

[@johnm2012]

The PNPN construction ironically makes it a three junction device and completely different from the original UJT such as the 2N2646, which had a slab of silicon with a base connection at each end and a single PN junction forming the emitter. A variation on the so-called PUT had four terminals (anode, cathode and two gates) and was called a silicon controlled switch. I still have some BRY39s in my collection.

[@johndododoe1411]

@@johnm2012 PNPN is also the thyristor construction, with back to back PNP and NPN as the logic-equivalent circuit. The naming of these components seem to follow the tradition of how advanced vacuum tubes / valves were named before transistors.

[@johnm2012]

@@johndododoe1411 The thyristor has a cathode gate, as opposed to the PUT's anode gate. The name "thyristor" is derived from "thyratron" (the valve, which has a similar "negative resistance" region in its characteristic curve) + "transistor" but I'm pretty sure the other names are unrelated to thermionic devices, which don't have any junctions at all!

[@FaustoTheBoozehound]

@Andrew_koala wow

[@Jadriam]

I know very little about electronic internals except 'don't poke around with it if you don't know how to put it back together', but Clive's calm voice is just so nice to listen to (and the fiery and/or explosive failures are amusing as well)

[@graemedavidson499]

Last time I replaced a PUT was in an industrial spot welder decades ago! It was used to set the weld duration. It must have made an impression for me to have remembered it:)

[@jeremywilliams5107]

Back about 1995, I was involved with the application of an ST Micro (I think) chip that governed all the indicators and hazards and could be mounted inside a standard hazard switch package. It could also diagnose the bulb states IIRC. This was just before body control modules started integrating the function and about the time instrument clusters went electronic, but way before generalised LED lamps in cars. Our target was Ford, but AFAIK it never actually got used.

[@jimmyhackers8980]

ive always found it funny that to get a "low power led indicator to work" you have to add a resistor so it draws exactly the same amount of power as a filament bulb :)

[@charlie_nolan]

Exactly, what’s the point if you’re adding a load resistor. Don’t do an LED retrofit if you’re not saving any power

[@Kineth1]

@@charlie_nolan LED retrofits aren't exclusively about power saving. They're also about physical durability, thermal control and bulb longevity.

[@charlie_nolan]

@@Kineth1 yeah, I know. It’s also safer in cars in some cases, because the bulbs are on instantly and don’t have to heat up to brakes and turn signals are more instantaneous on cars etc

[@jollyboyspecial]

LEDs don't just have lower power consumption than incandescent bulbs. They are also safer when they fail. LED "bulbs" are usually COB units with multiple LEDs and they tend to fail one LED at a time, meaning you still have some light rather than no light as would be the case with a single element incandescent lamp.

[@barquisimetido1]

@@charlie_nolan Someone told me that flashers designed to be used with filament lamps has a charateristic blink rate that lower its speed when a lamp goes out as a way to alert the vehicle's driver to correct the fault. The flasher relays are current dependent devices for correct working. So when you substitutes filament lamps with LED equivalents the flasher didn't flash at the legal rate or didn't work at all due the small current draw by LED lamps, the solution then is to use the resistors in paralell with the LED or change the flasher for a LED compatible one.

[@SeanBZA]

PUT can be replaced with 2 SMD NPN and PNP transistors to make a SCR. Easy to make the PUT using the standard transistor line, just need an extra diffusion mask step to get the PNPN structure in the die, as opposed to the UJT, which needs a lot more process work to get the diffusions right, in what is essentially a very lightly doped very long PN junction, almost JFET like in construction.

[@papaalphaoscar5537]

Wow! A relaxation oscillator. I haven't seen one of those in a long time also. Used to be used for sirens and dimmers.

[@ferrumignis]

Relaxation oscillators still widely used, just not ones based on a UJT!

[@bobblum5973]

Back in the '70s I recall seeing a UJT/PUT design relaxation oscillator that used a neon lamp. It was a ringer in a telephone! So instead of physical bells, it made a sound we referred to as "a 50 pound cricket chirp".

[@d.t.4523]

A couple years ago I made a circuit to flash the LEDs I put in my car. No point in buying the resistors they try to sell with them, to draw the switching current. Mine was a bit more complex, but I didn't try to refine it for production. I'm glad you made this one public. Cheers! Good luck! 👍

[@Thomamps]

This was a semester challenge when I did electrical engineering in the mid 90s Design and build a solid state flasher for a car, we didn't have MOSFETs and up to 72 watt loads were common.

[@philipwalker2800]

Remember looking at PUTs back in the 70's when I was designing a sound to light unit. In the end I used surpus/recovered NPN and PNP transistors (seemed cheaper at the time) to emulate the trigger fuction and drive the SCRs. It worked well for many years. Many thanks for the interesting (and sometimes scarey) teardowns you give us. Phil

[@tim1724]

It seems like an elegant design. Should be pretty reliable, too. I wonder what else those PUTs are used in; they couldn't have brought them back into existence just for something like this.

[@bigclivedotcom]

They were originally used for thyristor firing or timing. But probably find use in simple legacy circuits.

[@markfergerson2145]

@@bigclivedotcom I first saw UKTs in simple relaxation oscillators with variable time constant. The standard injunction as you said had a fixed trigger voltage set basically by doping levels. Varying the timing involved tricks with supply voltage which sometimes meant it couldn't supply the current you wanted. (UJTs are basically negative resistance devices. You can make them amplify as well as oscillate. I don't think PUTs can amplify.) PUTs being four layer devices (not literally injunction devices but they behaved a lot like UJTs) gave a lot more flexibility when you had limited voltage to work with but needed current without having to go full thyristor. I think the 555 is what made both of them if not obsolete, at least a lot less common. Like you I'm honestly amazed to see them in smd.

[@neilbarnes3557]

They must be used for something; digikey lists over forty types! Relaxation oscillators is where I remember examples from the seventies.

[@SeanBZA]

@@neilbarnes3557 Still plenty of old equipment that has them in it, where you need them to repair as they fail.

[@manolisgledsodakis873]

@@bigclivedotcom Something I must have been building back in the seventies. files.catbox.moe/eye6a1.jpg

[@lint2023]

Much experience and knowledge in the comments to go along with Clive. What a wonderful community you have created, Clive.

[@AztecWarrior69_69]

Thank you for this. Someone else did a breakdown video on this and had almost the exact same circuit. I though great I can use it in my simulator software. I am designing lighting configurations for kit cars, trailer lights, maker lights, hazards and turn signals. So I needed a 2 prong/pin flasher circuit. Well it wouldn't work because of the PUT. The guy didn't know it was a PUT. Was on the forums and all they kept getting stuck on is the LOAD. The damn load. They couldn't get passed me telling them, "It's not the load, something is wrong with the circuit" In any case after someone finally, left a link to your video. I knew you would have one on this but it would never come up on any search. Not gaagle not even directly here on youtube. I was able to find an alternative/equivalent circuit using regular transistors and now all is good. TY. Side note: I think the reason why the LED bulbs are not working is because of the load not having enough resistance BUT that is a non issue when in a vehicle. The amount of wiring to get to the bulb adds the resistance needed. So adding 3 or 4 ft of wire and it should work.

[@dizzy_derps]

I love when I'm watching a video before KZbin alerts me to the new video.

[@ebnertra0004]

That's interesting to see such a mix of technologies in one package. On a flasher-related note, I recently acquired a flasher relay for level crossing signals (Union Switch & Signal FN-16A) from 1956. It's primarily relay-controlled, but tge flash rate is adjusted by adding or removing copper washers from a pole connected to two big coils. I haven't had the chance to experiment with it, but I think it'll be pretty neat to see in operation

[@JimPatience]

I'll be honest and say that I don't understand everything you say (mainly due to lack of knowledge on my part!) but just to have your soothing voice on does help me chill out after a night shift.

[@Caluma122]

Thanks Clive, the amount of times I see this problem posted on my forum is unreal. So good to have a tear down and explanation!

[@ericwilner1403]

Cool! As you described what the module did, I started contemplating how I would go about implementing such a function... and found myself wondering whether unijunctions were still a thing (they were an oddity when I was a kid), and trying to remember, after all these years, how they worked. Interesting indeed that they're still around. Looks like the ones on the U.S. market ain't cheap... like, they cost more than a low-end MCU. Not priced for design-ins. I presume cheaper parts are around in certain overseas markets.

[@gregorythomas333]

Wow...haven't seen one of those in a really long time...pretty neat to see one here!

[@sandy7m]

I replaced the damaged rear light modules on my trailer with LED versions. Now the trailer module in the rear of the car does not beep when the indicators are on. I knew it was due to the lower voltage drop due the lower current demands of the LED lamps. but as the trailer lights ork without issues I was just going to ignore it. However, you have given me a very easy work around. Cheers for another really helpful tutorial.

[@siliconjunkie7297]

UJT’s were often used in strobe lights, when the UJT conducted it would discharge the capacitor into a transformer which generated the kilovolts necessary to trigger the xenon flash lamp.

[@VisDeux]

UJTs are the unicorns of transistors :D

[@flapjack9495]

Unicorn junction transistor!

[@ShaunieDale]

What a blast from the past! I just simply think of them as a P-gate thyristor. Make more sense than visualising them as a sort of UJT. I was thinking of the curious mix of old and new and then you said exactly that Clive. I’ve still got some 2N6028s somewhere. I remember we used to set them up as a very long interval low duty cycle flasher for LEDs that would run for several years off a couple of AA cells. The chief designer at the first company I worked for put a pair of LEDs in the eyes of a wicker, snake shaped plant holder in the stairwell. It flashed a very brief flash about once minute. People were never sure if their eyes were deceiving them!

[@hadibq]

wow that was an enjoyable discovery of that unijunction programmable transistor! Cheers Clive!

[@EVguru]

I built a device to do this over 30 years ago. A friend had a Triumph Dolomite 1850, that for some reason, would never flash it's indicators at an MOT compliant rate. I cobbled together a bridge recifier, smoothing cap, 555 timer circuit and a relay. Worked a treat, the only oddity being that it would continue clicking a few times after the indicators were cancelled, due to the size of the smoothing cap.

[@InssiAjaton]

My very first motor speed controller was based on an original UJT. Instead of op-amps, I had the sync reference swept over a pedestal step. The slope produced sufficient gain for the speed control.. One issue about the early UJTs was their trigger voltage ("intrinsic ratio") variation from unit to unit, so I had to grade them. Doing that grading, I noticed that there were zero UJTs with the nominal Intrinsic Ratio, only parts below some 90% and above 110% of the nominal. As there also was a tighter tolerance part listed, I concluded that the factory had already done their own grading. Another issue was the leakage current, which limited the maximum time delay obtainable. So, when, as I recall, GE introduced the PUT, and advertised its lower leakage current, I was intrigued by that. I never (then) used the new PUT, but I recall how a pal of mine utilized it in one or two of his designs. Just in case I would come across a new use for those ancient parts, I at some point purchased 10 of 2N2647 UJTs and 10 of the PUTs (forget the part number), and supposedly still have them in my collection. Which finally brings me to something that I never have had in my hands - tunnel diodes. I have occasionally checked, but could not find any availability. Some old Tektronix scopes used tunnel diodes in their trigger section to speed the response up.

[@RPS2443]

That's a great explanation of how a PUT works. I ran into one in an old DC motor drive in the 90s and didn't understand it well.

[@zenonkazienko988]

Wow I don't recall learning about PUT's in school about 15 years ago. But just this morning I sketched up a concept circuit with an NPN, diode to get a "switch" that would that would turn on at a certain voltage threshold. All I need is a PUT - AMAZING!

[@lightcapmath2777]

Thank you for this..old and new components...like the demo on using the LED and then the resistance correction. You Rock Big C! DVD:)

[@Nono-hk3is]

Clive, how could have doubted the iSesamo, even for a second?

[@markusallport1276]

What a great combination of components of different eras, thanks Clive!

[@alexdelara9858]

Cool one ! My first experience with UJTs (not programmable at the time) was way back in mid 70's where we used them as timers for strobe lights, mosquito repellers (it never worked lol).

[@richardsandwell2285]

One of the most interesting and useful videos I have watched in a while, fascinating.

[@geoffh2760]

I remember building a sound to light unit for a college project which used 2N2646 UJT's to fire triacs that controlled the lights. That was a loooong time ago... And then along came the 555 timer chip...

[@obe726]

That resistance testing thing is really really cool

[@kissingfrogs]

Resistance Wheel from Jaycar but they seem out of stock

[@TheBerk01]

Holy crapballs, i only put one of these in my bike last month after changing the front indicators to LED. Worth watching as always, thanks!

[@wimwiddershins]

The only thing missing is an audible click sound when it triggers. :)

[@ralphshoop8822]

Plenty of room in that case to add one!

[@timhartherz5652]

Simple: Put it a standard 4-prong case and hook up one of those mini speakers from an in-ear headphone between output and ground. You might need an resistor in series, and use the case as resonance corpus to amplify the noise. Should also act like the 1k resistor clive used to make it work with led's. Or leave it as it is and put the speaker across the mosfet.

[@kissingfrogs]

I always wonder if they were a legal requirement as its an audio reminder that your indicating.

[@juergenschimmer960]

You might add an Piezo-Disk in parallel to the Device. The Disk will probably fit into the case

[@wtmayhew]

I was going to comment the same thing. I was expecting to see a piezo disc and drive electronics in the case.

[@paulbattarbee9615]

One of the lesser known functions of the traditional automotive flasher was to monitor the lamp current so that if one of the lamps failed the flash rate would double, acting as a warning to the driver.

[@peterfitzpatrick7032]

More a by-product of the bi-metallic design than an actual designed-in feature... no ? 🤔

[@gadjetsvideo]

@@peterfitzpatrick7032 It is a legal requirement, in the UK at least, if a bulb failed it must flash at double the rate. Most modern vehicles flashers are controlled by a body control module nowadays with built in current sensing. Nowadays though a faulty bulb/LED can throw up a warning light on the dash.

[@Murgoh]

@@peterfitzpatrick7032 Probably yes but the "feature" is still replicated in some electronic flasher units as it's useful. Some will even flash the indicator lamp (with a separate output of course) rapidly if the current is too low while the actual turn signals still flash at normal rate. Also, many modern cars and trucks replicate the clicking sound of the old electromechanical flasher relays through a piezo disc or the speakers of the stereo system to indicate the driver that the flashers are on. At least I much prefer this to the annoying beeping that's sometimes used for the same purpose.

[@paulbattarbee9615]

@@peterfitzpatrick7032 No, part of the specification. I worked for Lucas and at one time maintained the test equipment on the flasher production line.

[@Hipcrostino]

It always surprises me that more people don't know this. It's been a standard feature for a very long time on the older bimetallic flashers.

[@stamfordly6463]

If you replace the lamps on a trailer with LED modules you need to stick a fairly big resistor on the indicator circuit. It can be a pain to find somewhere on (e.g.) an old Ifor Williams that gives you a metal backing to dissipate heat but is sheltered from dirt off the road.

[@andrewbancroft6174]

Elegant use of old tec. Love it

[@getcartercarpark.]

Now that cars use solid-state flashers that don't click, recent cars have a solid-state click sounder fitted to show the indicators are on. Not sure if it is an all-in-one device in my car, but you can tell it's not the bi-metallic strip clicker but some kind of sounder making the click as the indicators go on/off. Regards, K.

[@dougle03]

You will probably find that the computer does the flashing of the circuit via a mosfet and the clicking sound is coming out of your speaker system also generated by the computer. In my car, it's the BCM (Body Control Module). Modular mechanical relays are pretty much a thing of the past now in most modern cars, where they do exist, they have very few uses.

[@ferrumignis]

This kind of thing is done via a body control module these days, and they have a speaker for e.g seat belt warning tones that are also used to generate the fake clicking noise.

[@MarkGovier]

Modern? We were synthesizing the "flasher" sound (and many other beeps and bongs) for cars in the late 80s. Used a microcontroller. Programmable UJTs are great for overvoltage warning things too.

[@TestECull]

@@MarkGovier We had no need to synthesize that sound in the late 80s because in the late 80s we were still using the bimetallic flasher relays that clicked naturally. The need to fake that sound didn't arise until just a few years ago when marker lights started moving away from filament bulbs to low power lights that didn't draw enough current to trigger those old school relays. Matter of fact, back in the 80s, if a car had beeps and bongs each one had its own piezospeaker to do it. My 85 F150 had such a buzzer. I ripped it out and yeeted it.

[@MarkGovier]

@@TestECull you might not have, but some major global brands have been using electronic control for the lights since the 80s.

[@countzero1136]

Wow, what a nice surprise seeing a relatively modern device using a PUT. I didn't even know they were still available - I haven't used one of these since the 70s, when I used them to make very simple oscillators in my very first analogue synth design. That would have been around 1976 when I was still in school. Nice to see this very useful component again after all these years. Maybe Look Mum No Computer might try to get hold of a couple of these and build another simple drone oscillator as an alternative to the somewhat finicky reverse-avalanche design that most of these things seem to use these days... Fascinating stuff - You used to see quite a lot of designs in electronics magazines back in the day that used PUTs, sometimes as oscillators and sometimes as sensor switches - the sort of thing that you'd most likely use an op-amp or a CMOS logic gate for these days. Striking a blow for obsolete technology - bearing in mind that nothing is really obsolete when it can do the job you need it to do :)

[@iamdarkyoshi]

Huh, it's like a low frequency DC version of a triac based lamp dimmer in that it's purely in series with the load. Neat.

[@fromagefrizzbizz9377]

Isn’t this a SCR? You can make AC dimmers with them, the first dimmers were this way, but of course they were only half wave, and electrically they were very noisy.

[@colin4850]

First came across PUT' s when l was a photocopier engineer. When the toner bottle needed replacing it would switch the PUT on, it would then stay on until the bottle was replaced and the reset button was pressed. This would then break current flow though the PUT and the light would go out out

[@3rdpig]

I had all kinds of problems switching my old Jeep to LEDs. I used bulbs with built in resistors, used electronic flashers and could never get the flashers to work right until I found one certain kind of flasher called an EF32RLNP. Now it works with either LEDs or incandescents or a mix of both.

[@mylittleparody2277]

Thank you for sharing that oddity with us.

[@andrewwhite1793]

My first electronic project was with a 2n6027 back in about 1976. It was a bulb flasher too. A blast from the past. I can remember the part number without a prompt but where I put my car key is another story..😁

[@RHauto]

I bought a handfull of these over the years for my motorbikes, only ever had an issue with one unit recently where the bulbs stayed lit. Interesting to hear where they are used other than turn signals!

[@fidelcatsro6948]

these modules heat up when used, they should add a heatsink on the board to make them more reliable

[@TinySpongey]

Wow I remember unijunction transistors from my childhood in the 70s and early 80s. They were commonly used for simple oscillators and sometimes clock circuits for logic chips for a while in varous hobbyist magazines. The number TIS43 rings a bell as a commonly used device (funny how you remember things like that). The symbol I remember wasn't like that though (see the wiki page). They disappeared after a while to be replaced by 555 circuits instead.

[@johnconrad5487]

The symbol is of a PROGRAMMABLE unijunction transistor (PUT) whereas the other is just plain old Unijunction.

[@alandouglas8939]

Over 50 years ago my Dad made an electronic speed controller for my model railway. This used a PUT. First and only time I have ever seen one in the flesh. BTW. the speed controller still works after all this time.

[@EsotericArctos]

Some flasher cans had some kind of function that if a globe burnt out, they would flash really quickly rather than standard speed. These seem to be around for quite a while also. Would be interested to see one of that style at some stage too. Probably hard to find them now as I think they were primarily a mechanical relay still........

[@abpsd73]

I bought one of these a few years ago for the hazard flashers on my tractor. Seller's advert claimed "LED flasher" but of course it did nothing with a LED load, so I binned it and purchased a "two prong" flasher that had a ground lead, negating the need for external resistances.

[@hockeyguy820]

For at least the past two decades, the "clicking relay" sound of the turn signal in cars has been sampled and played through the audio speakers. I never noticed when this transition was made because the sound is so accurate. Younger people might not even realize that the sound is from an old school relay, or as Clive mentioned a bimetallic switch.

[@SeanBZA]

Or simply done with a small strangled chipmunk speaker in a sealed case, with a series resistor and capacitor to make it generate a pulse on every edge.

[@tin2001]

2012 i20 had relays. 2013 has solid state with fake sound. The Hyundai accent changed around then too.

[@n.shiina8798]

now that's new to me. thought they all emulated this sound on the cluster *on the new-ish car that utilize electronic flasher

[@JamesTK]

@@tin2001 car I had used a piezoelectric in the instrument cluster for all the beeps and boops. How most cars do it these days if they don't superimpose a signal over the speakers

[@klaust.2769]

Before digital playback some manufacturers used "audio relays". Their only funktion was to provide the clicking sound. The contacts, if present, were not connected.

[@LabArlyn]

Wow, I didn't expect this flasher would use ancient component such as PUT. I have this flasher lying around but with missing potentiometer.

[@Mike_5]

Some younger Electronics Apprentices would be scratching their heads at this but this is how it was done in the Good Old Days!

[@TBrady]

2 wire flashers are very common in motorcycles and old vehicles, this is definitly a bit different though. Good tear down and info.

[@wtmayhew]

I remember that. Flashers used to go bad pretty often. There was sometimes a bin on the parts store counter for about $0.50 each.

[@AMDRADEONRUBY]

It's indeed really interesting thanks Clive

[@BuyitFixit]

Great video Clive! I remember the old type that were also just an oblong bi-metallic strip with a line across it at 45 degrees (LUCAS?) that opened purely due to the current flow, and didn't have a heater. Seeing as you like reverse engineering, you might like my recent video on repairing a Dyson Fan (not the hot and cold one) as I reverse engineered the circuit that controls the oscillation motor. Or if you like software reverse engineering you might like the one I just did on an inverter password! Thanks again and keep up the great work!

[@KeritechElectronics]

Interesting. I thought it would be a multivibrator (555 or two transistors) driving a MOSFET, but I wouldn't expect the SCR.

[@SeanBZA]

Much cheaper though.

[@chrishartley1210]

And doesn't need a separate ground to power the 555.

[@foobar-9k]

I just have one of these flashers (from one of my bikes) open in from of me.. it has an M5233 (DIP8), and an IRF520... plus that damn piezo beeper so you don't forget to turn your blinkers off 😀

[@n7565j]

I remember having to buy "Heavy Duty" flasher modules for our vehicles back in the day since we pulled trailers which would cause regular flasher modules to flash extremely fast. They always worked, but if you didn't have a good ground, you'd chase grimlins for hours ;-)

[@KBilt92]

Makes me think of the 2 terminal delay-on-make solid state timer modules made by SSAC (among others). Not sure if these are common in the UK. Somehow they're powering themselves after the time is up and the load goes high - which is interesting because it might need to remain in that state indefinitely, so you can't just use a capacitor. Further interesting because some of them have a wide universal input rating, 24-240VAC/VDC. Would love to see a teardown of one of them, but you'd have to boil out all the potting inside.

[@deslomeslager]

Exacly what I needed! Orders placed .. .. Did not know they already existed.

[@MostlyInteresting]

The basic problem this relay is trying to get around is an old one. If you hook up a trailer and add its lamp load to the car, the flash rate would go way high. So you would swap out with a HD relay and then it would go normal, take off the trailer and it would go low or stop. Eventually solid state timer relays were developed and sorta fixes the problem with two wire relays. The other way that was common in HD vehicles (and bikes) was a 3 wire relay. Some like myself started adding trailer light relays to break the current dependence. They also allowed you to fuse for just the trailer connector, and take the extra load off the vehicle ckts. You could also translate the odd (for the US) euro taillight setup to the basic trailer light setup with a couple more relays. I worry that modern cars with LED's might not like a old trailer with incans, dropped on its ckts, so a relay box might be good there also.

[@bascomnextion5639]

In the 1980s I built an electronic unit to replace the bimetal type one so my dads car could pull a boat trailer and not go nuts flashing its indicators the 555 timer worked great and used about the same amount of components but the rules state it had to make the click sound and the receiver from a telephone did the job.

[@hellcattanks]

The venerable put, 2n2646 springs to mind, it was very popular in industrial controls. Electronic car flasher modules in the 80's & 90's had a current shunt, if one of the bulbs failed they flashed at 2x speed to warn the driver a bulb was dead, all done by the body module nowadays.

[@arielmateojesusdelacruz5186]

I read the titles in you're voice in my head💀 These videos are great content man this is my go to!

[@tchevrier]

in my first job out of school, I was helping test solid state flashers for busses. The worst test was the 1/2 amp load test. All the potted flashers would fail quite spectacularly.

[@AgentPothead]

I think you mean "best test" :D

[@tchevrier]

@@AgentPothead I guess that depends on perspective. lol

[@Eremon1]

What a coincidence. I was just wondering about the flasher module from traditional incandescent bulb vs what they do in an EV with LEDs. What a treat. Cheers.

[@AndyK.1]

They have been using FETs for years before EV came along. Even with lamps

[@Drmcclung]

In the very early days of automotive LED light conversion bulbs (about 20-22 years now) the top end bulbs would only sell in kit packs of however many lamps the particular car was designed to have (not usually sold individually) & either a new flasher or a huge resistor pack socket adapter thing to piggyback the old clicker. Which was fine for old cars still on the road back then.. was particularly a nightmare in new-at-the-time US spec GM & Ford pickup trucks that were sorty newly using BCM (body control modules) to control lighting and NOTHING would work right at all until you put the factory OEM spec bulbs back in. Made even worse by the fact I don't think there were even LED tech standards yet back then so there was no real way for an OEM to spec controllers around whatever was on the market. So we were stuck with incandescent for a long long time after their introduction. They were literally dark days, I'm so glad that's all over with now, LED had fully integrated, and people now know what they're doing

[@asciimation]

I thought one advantage of the old school bimetallic strip kind was if a bulb blew the flashing rate (so clicking noise) changed speed (increases) alerting the driver that a bulb had blown. It's a perfect example of how old school, analog tech performed a function that now you need a computer and software to do.

[@sharg0]

Both the fault indication and the sound are required in the EU, using this relay might cause issues at the car inspection. A beeper/buzzer in parallel should sort that.

[@Slicerwizard]

No, you don't. Plain old analog circuits are capable of measuring load and adjusting flash rate, or refusing to flash.

[@asciimation]

@@Slicerwizard Yes, that was my point. What used to be done electro-mechanically now has to be done with yet another computer and software in modern cars. Digital is not necessarily better. Think of it this way, in the old days, design a car, use a proven flasher module off the shelf and the functional requirements are met. These days you need multiple Scrum teams and sprints to implement 27 different user stories related to 'indicator function and fault indication'. And it will probably still have bugs in it. Not sure that's progress.

[@mikeuk1927]

@@asciimation But iNnOvAtIoN... There is no money to be made with simple, reliable and cheap solutions. You need complex, sometimes unreliable and expensive to make that sweet sweet buck.

[@wrongtown]

@@asciimation as a QA engineer, this comment made my afternoon 👊😁

[@graemezimmer604]

Brings back memories. The UniJunction Transistor was a very useful device. The 2N2646 is still readily available on ebay.

[@phonotical]

I used to sit in the walk in freezer under the fan in my t-shirt and apron, great way to cool down and get some fresh feeling air, I felt like I could stay there all day 😂

[@fidelcatsro6948]

i was trying to make my own flasher module last month and now this video appears!!

[@Graham_Shaw]

Gotta say, I've nevr even heard of a PUT before. Interesting stuff!!

[@ewhartiii]

I bought a couple of these to power LED turn signals on a bicycle. The pot can be used to adjust the flasher so it will work with LEDs without having a resister in parallel. I'm surprised that you didn't try that adjustment before using the resistor.

[@karlitosway4791]

At 1:30 comes this device in game with variable resistance. Where can I get anything like that?

[@wkearney99]

He did a video on it! kzbin.info/www/bejne/pGTNoKyKpNajecU

[@bigclivedotcom]

The resistor wheel is unfortunately no longer available.

[@Tore_Lund]

Got tired 17 years ago about swapping blinker relay in my car. Bought a 3 pin full electronic version for motorcycles and soldered the PCB from that into the housing from my old relay. This silent relay is now in my 4'th car Likely saved as many replacement relays in that period. MOT does not complain that there is no tick, they only care for the lamps blinking outside and on the dash. I'm not in the UK and they are maybe stricter, but that is one thing more with limited lifespan in my car I don't need to worry about.. Also saves a tiny amount of fuel, as I can run LED indicators, without a power resistor across to emulate a filament. Electronic motorcycle relays do not seem to care about bulb error by blinking faster. They almost all have the feature (or lack of). To add clicking noise if you really need it: One diode in series with a electrolyte capacitor, and a small headphone speaker, all mounted in parallel from the output of the relay to ground or + depending if it switches low or hi when blinking. The diode prevents reverse current in the electrolyte and you need a bleed resistor between Diode and electrolyte, to discharge it between blinks. The capacitor acts as a pulse shortener the short period it conducts on the longer DC signal to make a sharp click in the speaker.

[@Roy_Tellason]

I used to like fooling around with UJTs, they're quite varsatile little parts. Not easy to find these days, but you can effectively have one by cross-connecting a PNP and an NPN transistor, collector-to-base. This not only gives you a PUT, but also an SCR and SCS (another part I haven't seen in years).

[@threeMetreJim]

My favourite 2 wire flasher is on a site called techlib, under elctronics and flasher circuits. Works in almost the same way but uses a PNP and NPN transistor instead of the unijunction transistor. (3rd attempt at commenting, youtube spam filter keeps removing them...)

[@ElectraFlarefire]

Some blind searching finds that you can get the Mmbt6027/Mmbt6028 and CMPP6027/CMPP6028 PUT in a SOT-23 packages from a few places. Nothing with the markings you have. But still, a fun mix of old and new as you say. Good to see some people using these designs.

[@npiper]

In my own car I suspect the turn signals are on an RC flasher circuit with the bulbs providing the resistance since the moment I replaced the rear lights with LED bulbs the thing started going double tempo.

[@jagmarc]

@Echo_Hotel The traditional hot bimetal type requires two normal 21 W bulbs. Anything less it flashes a lot faster to draw attention a bulb somewhere has failed on that particular side.

[@michaelmoorrees3585]

Wow ! Haven't seen a unijunction circuit, for a long time ! At hobby level, its been replaced by the 555 for decades. A unijunction WAS most often used for making a low voltage avalanche relax oscillator. If your using a circuit with a power source greater than 40V, you can substitute a regular NPN with a DIAC. Maybe the Chinese are making these. I recently found a bunch in my parts stash, and gave them to a friend, who's big on making old 1960s circuits. I can't fault him, cause in the last 20 years, I've gone back to making vacuum tube circuits.

[@hobbesip1]

@2:40 Clive: "The spudger has won again" All: "All hail the spudger! Amen."

[@misterhat5823]

The body diode of a MOSFET is usually rated for the same current the MOSFET is. It's just much slower with a high reverse recovery loss. That's why it's shunted with a Schottky diode in switching circuits. In a lot of motor PWM inverter circuits we actually use the body diode as the catch diode.

[@user-mr3mf8lo7y]

I have same relay in my Yamaha SR250 for turn signals. Almost all of 80s/90s motorcycles have those installed. Works great. Also, just ordered a few 2N6027 to experiement a few things. Cheers,.

[@connclissmann6514]

Many thanks for the video of this cross-generational circuit.

[@megatronskneecap]

Hiya Clive! Used to watch your vids everyday till i got caught up in uni but now im back! Its so relaxing to see that classic wooden workbench with burn marks in it 🤣

[@tonyweavers4292]

I used to have an old Land Rover with a tired mechanical flasher. I replaced it with a three pin relay flasher after adding an earth connection. This is interesting though.

[@SeanBZA]

Funny enough replaced a tired 2 pin flasher on a Nissan van, and the official Nissan replacement part was a 3 pin flasher, with a tiny 3 pin to 2 pin adaptor, and a ground wire with a large lug on it, that you grounded to a nearby steering column bolt, which also was used to hold the bracket that the flasher was now attached to. Those 2 pin bimetal flashers were known to fail after around 5 years of intermittent use, despite being genuine Denso parts. LR used Lucas, which was intermittent from the get go, and of course you had a row of identical unlabelled switches, all of which do nothing, because Lucas. Constant indicator, intermittent flashing headlights and horn....

[@TYGAMatt]

Actually popped one of these open yesterday after it stopped working. Interestingly the transistor is what seems to be a 2N2907. The rest of the circuit was the same apart from a 1uF cap instead of your 3.3uF cap. I reverse engineered it and built it on a breadboard using a 2N2907 PNP and an IRLZ44N logic mosfet and it worked fine. I'm no expert on transistors but looks like putting a bias voltage on the base of the transistor also works then.

[@petehiggins33]

I'm amazed that so any of your subscribers remember the PUT from the 70s. Your audience is clearly much older than I thought.

[@BeezyKing99]

RE: 0:35... i have done this as a kid when LEDs first came out, 1 single diode, of course wouldn't cause the relay to trigger normally, but being a kid then and taking apart all sorts of electronics, my favorites were the lights.. took up to 8 RED diodes to trigger it normally (without resistors, I didn't know much about current/resistance values back then)... turns out, the bimetallic relays, can handle up to 10A-ish... found that the higher current going through it, the faster it'd trigger.... until the contacts would randomly decide to weld together.

[@Savage-lx5yj]

Excellent explanation sir! Thank you!

[@jms019]

I made one of these to replace the very r.p.m. sensitive bi-metallic strip one on my 6V MZ. Must have been thirty years ago now. Also worked on a body controller and used my own code to generate the noise for a synthesised relay noise. (Lucas.)