Scullcom Hobby Electronics #20 - Building a Constant Current Source Box

[@ivolol]

After many years I have designed / got manufactured / populated a circuit board for this project, also with 100mA range available. It has a calibration/operation switch which either provides a closed circuit over 6x120ohm resistors (20ohm effective) to measure 20mV/200mV/2V at a test point, or switches them out for the normal test points with which to source current. I also used 3 x AA batteries. I found 120ohm 0.05% resistors available at the time, but 5x100ohm might be the easiest for public to build. I was quite interested that to get 2V compliance I had to go almost to the end of my 1k pot! Thankfully not all the way to the end. I'm quite pleased that its my first semi-complicated circuit board I designed and it appears to work first try :D Thank-you for your project videos. 💕

[@juliench9997]

Hello ! I am using the LT3092 to produce a current of 100mA... but I am only getting 96mA at the end of the potentiometer. - For Rset, I am using two 39Kohm resistors in parallel + one precision potentiometer (30 turns) of 1Kohm (as shown in the video). - For Rout, I am using a 2-ohm resistor. Would it be possible for you to share your schematic, please? I am trying to debug my circuit and it could be helpful 🙏 Thank you

[@adamrouse6094]

I have watched your videos and I must admit I am impressed. I am an RF cell engineer with +20 years experience in product design. I have not found other videos which are as pleasant to watch as yours. You also like LT parts which gets my vote. You are doing a great job. I am looking forward to more videos soon. Thanks Adam

[@scullcomhobbyelectronics1702]

Thanks Adam for your kind comments which are much appreciated. Regards, Louis

[@basildouglas855]

A good project and excellent theory in this tutorial. So many videos and tutorials out there presented by other people, but very few manage to produce the quality in the presentation, the value in the theory and the skill with which you impart the knowledge. The world is concerned about global warming! There is a far greater danger that threatens society, and that is the irreplaceable loss of GOOD EDUCATORS.

[@PauloSilva-ll4vs]

Your channel is one of my favorite one, the dc load project was a state of the art, and now this one, I am imagining how wonderful should be your shop.

[@scullcomhobbyelectronics1702]

PARTS LIST 1 x LT3092 - Linear Technology 200mA Programmable Current Source I.C. (SOT23) [This I.C. is also available in a SOT223 - 4 pin package which you may find easier to solder, but it is usually £1 more expensive] 1 x SOT23 to DIP8 PCB adapter (can be easily found on eBay) 1 x Male Header Pins Strip - 8 Pins required for SOT23 adapter PCB ABS Plastic Box (Black) - size to suite project about w83 x h53 x d35 (mm) 1 x Matrix PCB Prototyping Board - cut to size (can be easily found on eBay) 2 x 1K - 25 turn preset resistor (good quality one if possible i.e. BOURNS) 1 x 3 Pole 4 Way Rotary Switch (silver contacts) - [only using 3 of the 4 way] 1 x Black Pointer Knob (Chicken Head Pointer) 2 x 39K resistor (1% tolerance) 2 x 100 ohm 0.1% Metal Film Resistors (used in series for the 200 ohm resistor) 1 x 100 ohm 0.1% or better Metal Film Resistors (used to calibrate the unit) 2 x 10 ohm 0.1% Metal Resistors (used in series for the 20 ohm resistor) 1 x Black 4mm Banana Socket (any type will do - but I used gold plated one) 2 x Red 4mm Banana Socket (any type will do - but I used gold plated one) (I used HIRSCHMANN TEST AND MEASUREMENT 930176700 SOCKET, 4MM) 1 x Battery holder for 2 x AAA Batteries with Flyingleads 2 x AAA 1.5 volt Battery OPTIONAL: (Not really required) 1 x Green LED (low power 2 mA) 1 X Plastic LED Holder 1 x 560 ohm 5% Resistor

[@supersilve]

I am impressed by the tutorials you give, I find them very useful. They are fully understandable. Thankyou.

[@Scorpio722]

Enjoying your well done videos and projects, thank you for the excellent quality, theory, testing, and techniques. There are a handful of providers doing this and you are one of those in the "Top Ten" in the world from my view. I had a thought that maybe a revisit to this concept would be great for those using "old school analog VOM/AVO". Many of the analog devices typically use 50ua 250mv for example in a Simpson 260, or a 60ua in a Triplett 300 series VOM.

[@victoribarra9930]

One of the best electronic channels

[@marsa74]

Excellent as usual. I hope all is well and we hear from you very soon. Take care.

[@marcelvanooststroom1733]

Very nice project. I have just made one myself. Thank you very much for this. The next project is your 5V reference which I combine with the constant current box in one project box. So I have a nice feature to check my multimeters.

[@scullcomhobbyelectronics1702]

Thanks for your comments and glad to hear you have found it useful.

[@thatonecamel]

Really enjoying your videos. I'm currently going for my electronics technology degree and these videos are actually helping me out.

[@scullcomhobbyelectronics1702]

+Thegreatmush Thanks. Glad you find them helpful.

[@rudrakshavegad1999]

Very nice project. By the way your current source is already very accurate. Here's how ,while watching the calibration part, one idea came into my mind . Why don't you just measure the output current of your current source and at that moment adjust the preset ( I mean trim it down until you see 1 .000mA and 10.000mA .) Its just that easy. If i am wrong please correct me. But iam pretty confident that this trick will work .

[@DavidWatts]

I was wondering at the start how you would deal with the accuracy of resistors (1-0.1% can be quite a big deal) and the 10 micro amps, great solution. Also, I am pretty darn jealous of your workshop. Really enjoyed the presentation style and detail.

[@scullcomhobbyelectronics1702]

David Watts Thanks David. I found that if you use all the same type of resistors then the tolerance is not critical as they drift by the same factor. The 100 ohm sense resistor I used to calibrate the unit is more critical but using a good quality 0.1% one works fine (alternatively you could use a 0.01% one but they are very expensive and this may be overkill for the hobbyist). Also use good quality resistor presets. With the resistor types I have used in the project the unit is accurate on both its 1mA and 10mA settings to at least 2 or 3 decimal places giving an accuracy of ±0.1% or better.

[@tseckwr3783]

Thanks for all your hard work and attention to detail on these instructional videos.

[@DJSolitone]

Brillant video from start to end. Excellent teaching !! Many thanks !!

[@scullcomhobbyelectronics1702]

+DJSolitone Thank you.

[@njnear]

Really enjoyed your presentation. Great job!

[@scullcomhobbyelectronics1702]

+NJ Near (njnear) Thanks.

[@DavidLeeMenefee]

I appreciate the time and effort you put into this tutorial. THANKS David Lee.

[@scullcomhobbyelectronics1702]

ElectronicWizzard Thanks David.

[@cncdavenz]

Very interesting video. Thanks for taking the time to educate us all. Cheers Dave.

[@scullcomhobbyelectronics1702]

Dave Bassett Your welcome.

[@mikeblankenship1985]

Very nice project!! I am using the LT3092 for use in a milli-ohm meter project Im using.

[@scullcomhobbyelectronics1702]

Thanks. If you check out my No 31 video you will find my project on building a Milliohm Meter which uses the LT3092. Direct link to my video below: kzbin.info/www/bejne/l5-oYZ16mqeortE I will shortly be providing an update to this Milliohm Meter project and provide details of how to get a ready made PCB for my design (the PCB is only 6.5mm by 4 mm and double sided).

[@mikeblankenship1985]

Scullcom Hobby Electronics Oh very nice project !! We are using almost the same config for the current source except were using fixed .5% resistors for SET and OUT, then switching the current between 10ma and 100mA using low resisitance opto switches. As of now we are using an LMP8350 PGA to test the different gains. Then putting the output to an LMP7704. No LCD yet just proof of concept, Ill be measuring the output with a Keithley DMM7510. I like how your videos go from a very high level concept down to the nitty gritty! Keep up the good work, I will let you know my results when they come in

[@PCBMakerBD]

Awesome tutorial and seems approachable.

[@g1fsh]

Nice video and a really useful project. I like this mini project format that u are using for your videos its excellent. Looking like a very good channel I cant wait for the next one. a basic cost for the projects would be helpful but I really like the way u explain things. Thanks

[@scullcomhobbyelectronics1702]

Gary g1fsh Thanks. The basic cost of the project was about £15. I will put together a full parts list and add it shortly.

[@dormantrabbits]

I really enjoyed this project video! It would have been nice to see some testing with an oscilloscope to check ripple and performance under load - just a suggestion.

[@scullcomhobbyelectronics1702]

dormantrabbits Thanks for your comments. I am mainly using my unit to quickly check the calibration of some multimeters on the current range.

[@doppey6]

Nice video I find them very useful and thank for the excellent theory

[@zx8401ztv]

Very well done, every step is discribed with clarity and i really like the rather clever 100R test resistor :-D. I also like the 10 turn trim presets, they cancel out the 10uA ref (as you said) and null out the operating/drive current of the op-amp, brilliant :-). I dont suppose a 10 million ohm (or more) volt meter would have much effect on the 100 ohm test resistor, too many decimal places down the line. So when are you going intp full production and competing with "dmm check" ha ha just leg pulling :)

[@scullcomhobbyelectronics1702]

zx8401ztv Thanks. Nice idea about going in to full production but I am doing it for fun and to help others!

[@saneeshelectronica9293]

Excellent video .how to make a variable o to 20 ma source with this?

[@MaddMart]

I'm fairly new to electronics and have just soldered my first SMD for this project. After I'd soldered it I thought I had shorts between pins 7&8 and 2,3&4. I was there for about half an hour trying to clean the solder up and testing for continuity when I suddenly remembered that these pins are connected internally. DOH! So I'm assuming I don't necessarily have to connect these pins externally as was mentioned in the tutorial? I have now ordered the items for the low current reference project. Keep the projects coming please :-)

[@scullcomhobbyelectronics1702]

Thanks for your comments. I find if you have solder bridging across SMD component pins the best way to remove it is with some solder braid (solder wick). Works quite well. Regards, Louis

[@MaddMart]

Yes, thanks, that's what I used. I've now finished the project and I'm pleased with the results... www.dolomitesprint.com/images/misc/CC1.jpg www.dolomitesprint.com/images/misc/CC2.jpg

[@scullcomhobbyelectronics1702]

Looks like you made a nice unit. Thanks for sharing the photo links. Regards, Louis

[@abscomm]

Great job, thank you. Not to be picky, but... at 12:22 you have drawn your third set of switch contacts incorrectly, that set should be in the middle position also. :)

[@kamingcheng4830]

Nice and detailed video for hobbyists, thanks

[@scullcomhobbyelectronics1702]

Ka Ming Cheng Thanks, I have some more planned.

[@kamingcheng4830]

Scullcom Hobby Electronics Great!

[@michaeld8975]

Your mechanicals are much nicer than mine. It must be the Harbor Freight tools I'm using? Handy little tester for sure.

[@scullcomhobbyelectronics1702]

Mooky Mann Thanks. I have had a lot of practice !!!!!

[@crowderglen]

Excellent video!!

[@microlab8]

And a suggestion. To make the calibration more accurate I would use high accuracy resistor. But these are too expensive to solder inside. What I've done is I made a resistor box with few very accurate resistors (0.005%) - from 200 ohm to 2 MOhm. Then you can use the resistor box outside of the current source box. Once calibrated you don't need the shut. For 1 and 10 uA you don't even need 4 terminal measurement.

[@scullcomhobbyelectronics1702]

Microlab Yes you could use an external resistor of 0.005% but these are very expensive for the hobbyist. I also build myself a resistor box with 100 ohm, 1k and 10K 0.005% resistors but this cost about £80. I found the 100 ohm shunt in the unit also helps with maintaining stable output current as the LT3092 likes to have some load on its out, so it served a dual role.

[@microlab8]

Scullcom Hobby Electronics Well I saved a little money by only buying two 0.005% resistors (the rages I need the most) and the rest were 0.01% which were cheap enough - $2 to $6. And they will complete the multimeter check set. Or one can buy only 0.01%. It's still good enough. And yes, stability in current sources can be tricky. I had a lot of problems with making stable current sources. I'm currently having a lot of ripples in a electronic load. It needs a bit of filtering

[@scullcomhobbyelectronics1702]

Microlab With regards your electronic load have you considered using some kind of active feedback loop to cancel out any ripple on the output load?

[@microlab8]

Scullcom Hobby Electronics Well, you are right. I don't have any feedback and that's probably the main reason it overshoots - the open loop gain is too high. I lost the schematic, but it's something like: powersupply.blogs.keysight.com/2012/08/how-does-electronic-load-regulate-its.html -similar to dave jones' dummy load. What would you suggest for the opamp gain. Is 10 ok? And do you think a capacitor in parallel with feedback resistor is a good idea - to slow it down a bit.

[@microlab8]

Microlab One thing is sure - the gain must be high enough to amplify very small current. I think 10 is not enough. One criteria was to be able to draw 1-2 amps from 1V battery. That's not an easy job with high shunt resistor. Low value of the shunt makes the voltage low -> needs higher gain. I think the transistor ON resistance is 0.0034 ohms at 10V GS (but I use 3.6). I think I use 0.1 Ohm shunt resistor. I have two ranges - 0.5A and 5A. The reference voltage (from a DAC) on the 0.5A range was about 0.3V. So if I need to setup 1 mA (as I can do now) I must set gain to 300mV/(0.1*1mA) -> 3000. Or 300 if I want the minimum current to be 10 mA. Well the DAC can output 78mV on it's lowest value, so I can reduce the gain by 4. Am I thinking right? (sorry for thinking in public :) ).

[@microlab8]

One little trick when calculating voltage/current/resistance. I like to round them to whole numbers, but make sure they are all the same magnitude. So if I want to calculate resistor from 200 mV and 10 uA values I convert the mV to uV. So it's 200 000 mV or 200*10^3. Then I divide 200 000/10 and it's 20 000 Ohms. If you are ok with working with power of 10 then it's even easier - 200*10^3/10 = 20*10^3 -> 20kOhm

[@scullcomhobbyelectronics1702]

Microlab Thanks. I usually use powers of 10 but I showed it in the video as a base number as I thought the hobbyist would find that easier to follow.

[@HitAndMissLab]

Brilliant tutorial. Thank you very much. This is better than Dave Jones ;-) Can this circuit be adopted for controllable variable current source?

[@scullcomhobbyelectronics1702]

HitAndMissLab Thanks for you kind comments. Yes the circuit can be used as a variable current source by simply making the Rout resistor (from pins 2,3 and 4) variable. I have thought about trying a Digital Potentiometer ICs (such as a 1K or lower) to see how that would work but have not done so yet. If you could uses a Digital Potentiometer IC then it could be controlled by a micro in I2C.

[@HitAndMissLab]

Scullcom Hobby Electronics Variable & programmable circuit would be great for transistor curve tracer. I like idea of a digital pots, but hey could notoriously stand only very small currents, around 10mA. problem with curve tracers under £100 is that they only cover a little bit of area above cut-off region.

[@boliljedahl6553]

Nice videos you are producing. Keep up the good work. I have a question concerning the LT3092. Do you think it is possible to control the output current with a voltage on Vset from 0 to 200mV? I am starting a project for a calibration unit which today using LT3092 using trimpotentiometer to control the current. I want to develop the system by replacing the potentiometer with a microcontroller generating a 0 to 200mV with a PWM output. Do you see any problem with this solution? The datasheet for LT3092 says that Iout=Vset/Rset.

[@robertcalkjr.8325]

Handy little project, thanks.

[@scullcomhobbyelectronics1702]

Robert Calk Jr. Thanks Robert. I found the unit to be stable and accurate and handy to check handheld multimeters on their current range.

[@robertcalkjr.8325]

Scullcom Hobby Electronics I already have a DMM Check Plus that I bought from voltagestandard.com, but this would be a good project for someone that would like to build their own current checker. I would build projects and stuff when I first started learning electronics a few years ago to increase my soldering skills. Plus the added pleasure of having useful devices and tools.

[@timothysvec8568]

Well done sir.... Well done! 😀

[@scullcomhobbyelectronics1702]

timothy svec Thanks.

[@BlensonPaul]

very professional. loved it !

[@scullcomhobbyelectronics1702]

Thanks.

[@questioneverything6860]

A really useful and informative video.

[@scullcomhobbyelectronics1702]

Thank you.

[@rfdave3980]

Hats off to you Sir. Excellent

[@scullcomhobbyelectronics1702]

Thanks. Regards, Louis

[@sarathchandran8188]

can i use rout 2 ohms and to make 100mA ? and after that parallel 4 such sources to get a 400 mA current source ? will i get this much accuracy and tollerence ?

[@coreyhulse8226]

Thanks for the video! One quick question around the 10:00 mark, when you add the 100 ohm resistor on the output to measure the voltage drop across it, wouldn't that change the effective resistance you see on the output of our current source? Effectively changing the output current from the 1ma we want? Thanks in advance for any help! Edit: I see I think I see what you are trying to do, you are putting in that 100 ohms and monitoring the drop across it so that you know WHEN you have tuned the circuit to output 1ma, I thought you were putting it in to test IF it was outputting 1ma like it should and thought the resistor would screw that up. Am I following your design logic correctly?

[@scullcomhobbyelectronics1702]

Thanks for your question. The set current is a factor of the values of Rset resistor (from pin 5 of the IC) and the Rout resistor (from pin 2,3,4 of the IC). The other end of these resistors are connected to a common return point (joined together). It is at that common point that the current is set to the required level. Since we are adding the 100 ohm resistor after that point it will not effect the current set. We can therefore use the 100 ohm resistor as a means of measuring the current during set-up. Any value resistor added after the common return point I mentioned will have no effect on the current set. I used a 100 ohm resistor since 1mA flowing though it will give 100mV across it, which is easily read on a multimeter. If you were to change that resistor to say 10 ohm you would still have 1mA flowing through it and in that case you would read 10mV across it. The reason I chose to use a resistor (100 ohm) to effectively measure the current is that on a cheap multimeter the accuracy on the millivolt range is much better than the accuracy on the milliamp range. So it makes sense to use the most accurate option. Hope this helps. Regards, Louis

[@Kamal-qc2qf]

Very useful video sir. I have 100microammeter analogue pls get to convert to digital reading,as in internet I searched all are measuring above value

[@gkdresden]

Is the minus terminal of devices in GB on the right hand side? We have it on the left hand side in Germany.

[@scullcomhobbyelectronics1702]

Anyone interested can download an actual size image of the front panel template in PDF format. Link below: www.scullcom.com/Scullcom_Constant_Current_Box_Template.pdf

[@proyectosledar]

The quality of your videos is excellent, congratulations. which camera you use? I would love to have that quality in my videos but surely can not buy that camera. regards

[@scullcomhobbyelectronics1702]

Proyectos LED Thanks. The camera I am using is a Panasonic HDC-SD90 Full HD. Its nothing really special but the set up I have to film helps.

[@xfran70]

Veo que coincidimos en todas partes, que pequeño es el mundo !

[@Aviprink]

I want to make it for my milliohm meter project .

[@cheapmod]

Thanks for sharing your knowledge.

[@Graham1904]

Why didn't you calibrate the unit by measuring the current rather than the voltage across the 100R?

[@shivamprakash8194]

I was wondering that too, I think the current accuracy of a multimeter cannot be trusted. I think he mentioned that in the video too

[@martinda7446]

Measuring the voltage is non intrusive, you don't alter circuit or add unknowns, leads resistance etc. into the circuit. A precision resistor of low value, often parts of an ohm, to measure voltage drop is standard way to gauge current in any circuit.

[@martinda7446]

Plus the current ranges on cheap meters are often poor. EDIT: Which is why this project exists.

[@stephanc7192]

I always like your videos!

[@scullcomhobbyelectronics1702]

Thank you.

[@BeetleJuice1980]

dear sir , excellent project ! may i ask a simple question if you dont mind : cant we power these instruments you make from a power supply and not batteries ?

[@scullcomhobbyelectronics1702]

Yes you can power them from a DC power supply.

[@muhammadhassanulhaq]

Hi there, nice project. Very useful. Can you tell me from where can I get 0.1% resistors?

[@scullcomhobbyelectronics1702]

Hi, You can find 0.1% resistors from many suppliers such as DigiKey, Farnells (Element 14) and Mouser. You will also find then on eBay. Regards, Louis

[@sirajhussain791]

Excellent

[@andymouse]

Awesome.....cheers.

[@moustaphamuhammad7013]

Can you make a video on how we can design a 4 to 20 mA circuit? just for testing a new module or PLC cards. Thanks!

[@scullcomhobbyelectronics1702]

Hi Moustapha, Thanks for the suggestion. I do get a lot of requests for projects. it is just finding the time to do them all. Regards, Louis

[@BBruno185]

Thank you

[@BeetleJuice1980]

can we power this project with 5vdc through a micro usb and maybe a pc usb port (or a cell phone adapter)?

[@markusherrmann9681]

Would the accuracy of the unit be improved by meassuring the exact value of this uniqe shunt resistor and calibrating to the calculated voltage drop? In this case, also a resistor with higher tolerance can be used?

[@scullcomhobbyelectronics1702]

Markus Herrmann Yes you could measure the resistor first and then use that in your calculation but then you are relying on the accuracy of your ohms reading on the multimeter. In any case if you use a 0.1% tolerance resistor the voltage error read across the 100 ohm resistor is very small, for example on the 1mA output, if the resistor was out by say +0.1%, the actual resistor value would be 100.1 ohm. If you then adjust for 100mV across it the actual current output would be 100mV divided by 100.1 ohm which would equal 0.999mA (so the maximum output current error is only ±0.001mA). As I have I mentioned earlier you could use a 0.01% tolerance resistor but for the hobbyist they are very expensive. Another option I have used is to connect 10 of 1K 0.1% resistors in parallel to give 100 ohm - this improves overall tolerance. Thanks for your question.

[@dreamfly555]

For calibration, can you simply measure the voltage at pin 5 for 200mv while adjusting the 2 adjustable resistors?

[@ivolol]

I don't think so, because the current of the 200mV from the SET pin is being added the out current from the OUT pin, we are looking for the current that occurs on both added together, not only one.

[@DarianCabot]

Excellent video, thanks

[@scullcomhobbyelectronics1702]

Darian Cabot Thanks Darian.

[@tuberlook1]

Very well presented. I am guessing you teach electronics/engineering ?

[@scullcomhobbyelectronics1702]

tuberlook1 Thanks. I used to teach electronics many years ago when valves had not quite gone out of fashion !!!!!

[@litheshkannagm5306]

dear sir, great video sir... I need 100mA constant current source. by changing Rout resistance to 2ohm, will I get 100mA constant current source?

[@scullcomhobbyelectronics1702]

Yes a 2 ohm resistor for Rout will give 100mA constant current source.

[@gorillaau]

Scullcom Hobby Electronics Which raises the question, what's the maxium currrnt that can be supply through that chip?

[@abdallahtlayss8601]

شكرا

[@kikibarrios]

Excellent, keep it up. Thank you.

[@RichLeespage]

Another fine project for me. :)

[@scullcomhobbyelectronics1702]

Thank you.

[@正直誠信]

Do you have any good suggestion for a 10A constant current source circuit?

[@RexxSchneider]

It will depend totally on how much voltage you want to have available. Let's say you want 5V, so the maximum resistance you're driving current into would be 0.5Ω. You are going to be supplying the current via a power BJT or a power mosfet, so when the resistance you're driving current into is 0Ω, all of the 5V will appear across the transistor plus whatever voltage is needed to run an opamp, and with a current of 10A, it will be dissipating more than 50W internally. So you need heatsinking to remove that 50W. Clearly, if you want 10V available, you will need heatsinking capable of cooling over 100W, and so on. Getting hot will usually cause some drift in the output, so you'll need decent cooling and design the circuit layout to minimise the heat near sensitive components. As for the circuit itself, you can copy the internal schematic of the LT3092, i.e. a current source, an opamp capable of operating at low voltages, and output transistors capable of handling 10A and however many watts you decide on. You don't say how stable or precise you want your 10A source to be, but that will determine how accurate and stable your current source has to be. Maybe an LM334 is accurate enough? It will work with as little as 1V across it.

[@irawarnaca8133]

That was great! Thank you.

[@scullcomhobbyelectronics1702]

Thanks

[@techNK12]

Where we can use this?

[@cheewurz]

I have a little Circuit you might be interested in.

[@nrth3rnlb]

Great, thank you

[@shivamprakash8194]

I think you should have calibrated your current source with multimeter in current mode, unluess you are using really precise resistors

[@perrieiles493]

Checking the capabilities of the chip, it shows it can handle 400mA - i am wondering how we could add a third level for 100mA - and i would really like to add 1.000A - but do not know where to go with that (or if it is possible) . Ultimately i would like a 2.0000A or even 1.90000 reference for checking multimeters. have obtained 2 of the chips so can build a second unit. Currently using a GW121 (EEVBlog DMM on KZbin) . also obtained an 8W 100 ohm 0.01% 4 leg (kelvin) resistor from the UK - please let me know, i cannot find a multimter than has

[@ivolol]

Already at 200mA you would likely want heatsink, at 400mA you likely want heatsink + active fan. For most electronic parts, the top of their power rating always practically involves heatsinking+airflow for the unit to dissipate its heat at that rating, it usually cannot do it with just the case to ambient air. Although the datasheet does also demonstrate paralleling units for ease of power distribution. However for a 1A constant current load, I would suggest it would be more practical to build an "electronic load" combined with some (lab) power supply, which has the ability to be set to 1A in some calibrated fashion. The currents the LT3092 is mostly designed to be used for is in lower mA range. I guess you could design an electronic load around an LT3092 providing a core reference as well, that is one design option amongst many, but its starting to be far more complicated than the design in the video. That all said, yes it's indeed possible to build it for 100mA, I have just done so. The only worry is that its likely to heat up a little during prolonged operation (also - when battery powered, your batteries will drain fast!) and critical parts heating up always gives way to temperature coefficient (tempco) errors as well. That, I will just have to live with for that range.

[@BeetleJuice1980]

is this keithley so accurate that you use it to calibrate other instruments?

[@BeetleJuice1980]

and how can we calibrate our cc units without a keithley?

[@scullcomhobbyelectronics1702]

Although the Keithley 2000 has a DC Voltage reading accuracy of 0.003% and is good to use if you have one, most low cost multimeters still have an accuracy of 0.1% or better on their DC voltage ranges (such as the Uni-t UT61E which only costs about £36 new on eBay) and would still OK for calibrating this project. Setting the 100mV and 10mV in calibration as shown in the video would only result in an error of 0.1mV and 0.01mV respectively at worst. In essence if you use a cheap multimeter to calibrate this project the reference current it then produces will still be accurate to ±0.1% or better, which means it is far more accurate that a cheap multimeters DC current ranges would be.

[@steverodgers1112]

What process do you use to create the templates for the project box? I've been looking for ways to do this easily on Linux. Is the software you use a CAD package, or is it some other software or is it some drawing package like CorelDraw?

[@scullcomhobbyelectronics1702]

Steve Rodgers I currently use Paint shop Pro. Software which I have had now for some years.

[@steverodgers1112]

Thanks. I like your idea of using labels bomb-sight drill locations. I've since figured out a way print panel labels using Kicad and water resistant label stock with a laser printer. First, draw the outline of the front panel on the edge cuts layer. Then use the drawing layer you can mark the drill locations and add label text. If you print it 1:1 you get a nice looking front panel with all the drill locations marked.

[@dibraniuk]

hi, can you please post a link for smd to dil adaptor very good explaining. thank you

[@scullcomhobbyelectronics1702]

www.ebay.co.uk/itm/SMD-to-DIL-DIP-adapter-board-SOT-23-to-3-6-pin-DIL-DIP-/112000708067?hash=item1a13c32de3:m:maqQcTbmOPOBO2-aDxjC2fQ You will also find these available from China on eBay much cheaper but will have to wait longer for delivery. The LT3092 also is available in a 3-LEAD PLASTIC SOT-223 which is easier to solder to.

[@dibraniuk]

thank you, can see they are 2- 6 pin! doesn't the lt3092 needs 8 pin adapter?

[@scullcomhobbyelectronics1702]

Apologies sent you the wrong link by mistake. The correct link is below: www.ebay.co.uk/itm/PA0089-Proto-Advantage-Adaptor-Sot23-8-Tsot-8-To-Dip-8-0-65mm-/271985161412?hash=item3f539434c4:g:ZnEAAOSwyvBV9ZPR

[@crector12]

I need a DC current source (range 10 to 200 uA). Will this work?

[@scullcomhobbyelectronics1702]

+Charles Rector The LT3092 chip uses an internal 10uA current source which is at the SET pin. For DC source currents of 100uA to 200uA may be possible - use the formula to calculate the resistor values and give it a try.

[@renekenshin6573]

Nice project, but soldering that small thing would be a pain in the butt.

[@scullcomhobbyelectronics1702]

Yes it can be a bit tricky but if you use fine solder and a desk magnifier light I find it works out OK.

[@sciencetroll3208]

You've drawn this in a very confusing way. According to how it is drawn, the input voltage is wired and soldered directly onto the points marked as set and out.

[@scullcomhobbyelectronics1702]

The bottom of the SET Resistor and the OUTPUT Resistor must share a common connection point. Not sure what your point is as the Input Voltage is not soldered directly onto the points marked as set and out.

[@Aviprink]

Sir I did't find this IC in my local market. Can i make a precision current source using . TL431 Precision voltage refrance for opamp and mosfet for constant current mode.

[@scullcomhobbyelectronics1702]

Hi, The LT3092 has an internal precision 10uA current source and so this IC is idea for this project. You could build a precision current source using an accurate voltage reference, Precision OP Amp with a very low offset voltage and a transistor or Mosfet. If you look at my DC Load project videos that will give you some ideas how to go about it. You did not say which country you are in but have you tried DigiKey or Mouser for the LT3092 it should be available. Regards, Louis

[@truongsumobile]

I like!

[@scullcomhobbyelectronics1702]

Thanks.

[@SureshKumar-nk2ok]

respected sir.....this is not related to video. i have a simple question,i damaged 50k pot while removing the radio set,i found 1k pot in my cupboard ,and i need to convert this for 50k pot so started connecting parallel resistor iam unable to find solution for this,pls share some idea how i can convert this 1k pot to 50k pot and i dont want series resistor to connect along with 1k pot.

[@scullcomhobbyelectronics1702]

I think the cheapest and simplest solution would be to buy a 50K pot. If you really wanted to use a 1K pot then to convert to 50K you could do it using a 50K Digital Potentiometer IC controlled by an Arduino Pro Mini which itself is then controlled by your 1K pot (but you would also need 3.3v or 5v power for these components to) - but this is a costly way of repairing your radio. Better just buy a 50K pot. Regards.

[@SureshKumar-nk2ok]

Thank u very much sir.

[@questioneverything6860]

Subscribed

[@scullcomhobbyelectronics1702]

Thanks.

[@mshahabas]

there is a samsung phone dying there:) how long it will last on batteries? I'm guessing pretty long... just curious.

[@scullcomhobbyelectronics1702]

m abraham A standard Duracell Long-Life Alkaline AAA 1.5 Volts battery has a capacity of 1000 mAh. As the Current Source Unit unit only draws power when in use the average power consumption is very low. If you assume you use the unit say a total of 1 hour a week and the current load can be either 1mA or 10mA (excluding the LED which is not needed, which in any case is only 2mA) then worse case at 10mA load for a total of 1 hour a week would use 10mAh - which would mean it would last 100 weeks or say 2 years.

[@mshahabas]

Scullcom Hobby Electronics hi, where did you get this number 1000mah? from what I've heard and research the best and most for AAA ones is 750mah for AA its 1900 for the best case! Thanks

[@fpliuzzi]

m abraham Interestingly, the datasheet for the Duracell MN2400 Long-Life Alkaline 'Copper Top' AAA battery shows a rated capacity of 1150mAh (to 0.8V per cell). www.alliedelec.com/duracell-mn2400bkd/70149226/

[@mshahabas]

fpliuzzi alkaline (primary in general) batteries are a big mess, maybe there is a reason??? wondering about that a long years now! Can first tier manufacturers/brands publish clear documentation datasheets etc... how come they avoiding to do that this long???

[@markr.pettitt845]

Anyone have a copy of the front fascia they could share with me?

[@johnconrad5487]

if u really want accuracy u need to use 0.1% resistors.

[@scullcomhobbyelectronics1702]

Yes you could use 0.1% resistors.

[@sciencetroll3208]

Everyone else uses a dot to signify a soldered join.

[@scullcomhobbyelectronics1702]

Thanks for your comment. Did I miss some dots.

[@ShelliLoop]

Dont you have ZERO in your vocabulary? “0” isnt called KNOT or NOT. It is ZERO. Why cant you say ZERO? THANKS. And “Al-you-mini-yum” is a goofy way to say aluminum. Al-lum-i-num.

[@Graham1904]

Why didn't you calibrate the unit by measuring the current rather than the voltage across the 100R?

[@scullcomhobbyelectronics1702]

+Graham Gillett Thanks for you question. You could measure the current but most hobbyist may not have access to a high accuracy current test meter. But most cheap multimeters today are very accurate on the voltage ranges (but not on the current ranges) so I thought it best to measure the voltage across a high tolerance quality 100 ohm resistor. I used a WELWYN RC55 Series 100 ohm 0.1% resistor. This worked very well in this project. As you can see on the video I used a Keithley 2000 bench meter which is very accurate on both voltage and current but most hobbyists may not have such a meter. The idea was to make it easy to use any cheap multimeter. I did show the current readings on the Keithley 2000 at the end of the video just to show how accurate the calibration method was. Hope that answers your question.