Making a Wien Bridge Light Bulb Oscillator - DC to Daylight

[@andye2005]

Trip down memory lane... (I call them "Ven" bridge) 40 odd years ago I was building part of a test rig for marine RADAR systems, and one of the requirements was to feed in a signal that would produce the classic rotating trace. This was usually produced by a selsyn of similar mechanical motor device connected to the scanner gearbox The rotational speed of the scanner is something in the 1-2 rpm range. So I used the Wien bridge circuit, which was well suited for such low frequency. The cct was almost exactly the same, as yours using the 741. The light bulb was a small "pea" bulb that was normally used for panel or meter lighting. Fed the output through a buffer, then into a phase shifter, and into more buffers to get the sine/cosine waveforms to drive the PPI (Radar Tube) The test rig was able to take half a dozen Radar sets, simulate the inputs, and monitor various voltages and so on, all while bumping the sets up and down at about 6G! Fun days! Andy

[@AmRadPodcast]

Thanks Andy. I really enjoy hearing stories like these, especially when it involves 'old' analog solutions. That sounds like it was a fun project to work on. Would love to have seen it in action! -Derek

[@IanSlothieRolfe]

Back in the late 70's when I was starting out in electronics and got to learning about op-amps with my Dad, I experimented with 741's and found generally you got best results using fairly high voltage balanced power supplies - at least +-9v and +-15v were best, and designed the circuits to keep the signals well below that at all points in the circuit because the 741 isn't very good when the the output approaches one of the power rails. We were making circuits from magazines and then tweaking and modifying them to incorporate into a synthesiser project (as was everyone else in hobby electronics at the time it seemed!) or just to see what would happen. My synthesiser got interrupted by University and never completed :) However, for a simple circuit the one you show got some impressive THD results with minimal optimization, so well done!

[@josefjelinek]

Very refreshing video which keeps me subscribed.

[@Gary-vo9rm]

Very nice seeing this explained. OG, retired, newby (2-3 yrs) just beginning to mess with frequencies and ran across this just last week by accident. 555 & LM358 opamp. I'll sometimes run an "on" LED on new circuits and found if I removed it, the signal goes flat, otherwise a beautiful signal. Now I just need to figure out what to do with a pretty sine wave cause I know people use these for stuff :-) edit: I think my results are probably from different reasons than what you show here though

[@petersage5157]

Love to see a nice dive into this kind of circuit design! There are a few others about Wien Bridge oscillators on the KZbin, but this is among the best I've seen. Some of the noise in your measurement is probably coming from the TL082; the TL072 has a lower noise spec. Wouldn't be surprised if some of it is shot and thermal noise in those carbon film resistors. Also, unless you SOT'd the resistors and capacitors, a mismatch in the filter network could be contributing to the distortion. I've often wondered why we never see low noise chips like the NE5532 used to build a Wien Bridge oscillator. The early ap notes tend to specify a BJT input op amp like 1/4 LM324, so it seems to me that the 5532 should be perfectly suited to the task.

[@PapasDino]

Nice review! I did steal a screen shot of your time vs. frequency domain to replace the one I have in our Ham upgrade courses. 73 - Dino KLØS

[@donaldfilbert4832]

me too !!

[@jstro-hobbytech]

I have the same Steinberg urII. Cool use of it man

[@qzorn4440]

o yah, The oscillator is based on a bridge circuit originally developed by Max Wien in 1891 for the measurement of impedances. 🧐 i love the 741 op amp 🥰 thanks

[@jameshall5835]

I made the Wein oscillator in Mr. Carlson’s lab with the TL072 and the 7387 bulb. Very interesting project ! I got it to oscillate at 17 kHz.

[@AmRadPodcast]

I hadn't seen that project.. is that a patreon member thing? He's got loads of great content. -Derek

[@jameshall5835]

Yes, I believe this is a Patreon thing. It was one of his earliest and I believe he later incorporated it into a curve tracer project. Bright guy !

[@FEPLabsRadio]

Cool video. Thanks!

[@AmRadPodcast]

Thanks Jim!

[@mumbles1justin]

Great Video. So I guess thats why inductive loop modules for automated gates and traffic lights have bulbs inside them? The bulb basically stabilizes the 100khz loop signal that energizes the pickup loop?

[@AmRadPodcast]

Honestly I have no idea. I've never seen the inside of one of these systems, though I poked around the internet for a while. This looks like an interesting topic, where the vehicle 'detunes' the tank circuit and they can use that to detect traffic. Thanks for bringing that up. Not sure about how the bulb relates to this system - I'd imagine they'd use more advanced oscillators nowadays for the application. -Derek

[@mumbles1justin]

@@AmRadPodcast The bulbs are in the currently made modules.

[@mumbles1justin]

@@AmRadPodcast Is there a way for me to mail you a EMX D-TEC loop detecter? Maybe you could use it in a video?

[@arthurharrison1345]

​ @AmRad Podcast Some loop detector designs use neon lamps as surge arrestors. This wouldn't relate to the purpose of the incandescent lamp in the Wien bridge oscillator. Loop detectors often use resonant L-C oscillators that follow the form of a Colpitts design.

[@a531016]

Excellent T-Shirt... And Great video too!

[@AmRadPodcast]

It's all about the shirt!

[@sebastian19745]

741 works better with dual power supply (+/-9V I mostly used, but is good at +/-12V too). Wien bridge can be used in RF too, is not for low (audio) frequencies only. I made a RF oscillator for my lab using a variable air capacitor for tuning and inductances, and as amplifier I used BF transistors.

[@ZPapaGeek]

You should check out how Hammond organs use of light bulbs to limit the input signal from the main amp to the reverb amp.

[@blg53]

Could you please explain how the variable resistor (the bulb) works in this circuit. In the diagram it shows the bulb is placed between inverting and non-inverting inputs. I expected it to be between non-inverting input and ground, then I understand the AGC effect. But in this circuit? Is there an implied voltage divider that includes the bulb and the low-pass filter as well as the 500 Ohm potentiometer?

[@martinmartinmartin2996]

Question: the tolerance of the Hi/Lo pass result in frequency uncertainty. Is there an analysis somewhere that shows the effect of frequency vs component tolerance at say 1 Khz?

[@peterrhodes5663]

Please explain how the circuit, as depicted in your schematic, oscillates, when one end of the bulb is not connected directly to ground/ 0 volts.. I've tried to match this with your actual circuit, but it's not shown in full.

[@jamescollier3]

look up how opamps work

[@peterrhodes5663]

@@jamescollier3 I first did that 50 years ago, and have built Wein bridge oscillators using bulbs and thermistors ( R53's ). One end goes to ground, not into the parallel RC part. So can you make it work, the way that it's drawn? I encounter too many incorrectly drawn circuit diagrams on YT. If I were younger, and trusted the accuracy of those diagrams, then I would have spent endless hours being frustrated by non-functioning circuits, not knowing if I was the problem, or the components. So, if you have never constructed an oscillator that is wired exactly as per the drawing in the video at 1:36, then please refrain from commenting, because you are simply compounding the problem

[@andymouse]

Or look at his diagram and then the way it is set up on the breadboard they are different. In the breadboard the bulb is clearly grounded at the same place as his scope probe. so the diagram is wrong as for whether it works as per diagram I will find later. Also on the breadboard he has 2 decoupling caps that aren't on the diagram so adding yet more confusion for the novice@@jamescollier3

[@andymouse]

The diagram is not what he has on the breadboard, take a look. Also the breadboard contains 2 decoupling caps that are not on the diagram either so be careful that could cause confusion. I expect you have sussed it all out by now ! but you were right to question it see my comment below.

[@peterrhodes5663]

@@andymouse It's not rare to find schematics drawn incorrectly. Sometimes, as in this case, I highlight them, because it must be very frustrating for someone new to electronics, trying to get a circuit to work as per the schematic, when it never will. My signal generator works from a Wien bridge circuit, but uses an R53 thermistor. Built nearly 50 years ago. Unfortunately, I have to tolerate stupid comments, like the one above by Mr James Collier. Thanks for contributing Andy.

[@farhadsaberi]

I didn't have money to buy an LCR meter so I built the clapp oscillator to measure my inductors.

[@AmRadPodcast]

Interesting application. This would be fun to do a video on. -Derek

[@farhadsaberi]

@@AmRadPodcast This would be a very important and informative video. This info is very hard to find for hobbyists like me. There's only one out there that I learned from. You should make a video showing how to measure capacitance with an oscilloscope (for better accuracy of the capacitor's value) and then use that value to measure an inductor's value using some LC oscillator. Thanks.

[@petesapwell]

So the WEIN BRIDGE, was a thesis paper ? And made HP…incredible, all because a guy discovered a incandescent bulbs resistance is dependant on its temp, PTC OR NTC? Can’t think which way around that is.

[@arthurharrison1345]

The lamp exhibits a positive temperature coefficient; its resistance increases as the voltage applied to the filament increases.

[@Don-mg1kl]

Can you guys do a classic. Make a ps5 or Xbox laptop

[@MuellerNick]

As Max Wien was a German, his name is pronounced ween (with a long eee).

[@fer_fdi]

Usually the lamp goes to GND... strange.

[@MAYERMAKES]

I pronounce it Wien ...like in Wien the capital of Austria.

[@AmRadPodcast]

I'm going to call you the expert on this one. (I defaulted back to the pronunciation I adopted back when I was a kid, reading my dad's textbooks!). -Derek

[@manyirons]

I've always pronounced it "Vine" but according to Wikipedia that's not correct either. Same as vehicle "VIN" would be better.

[@manyirons]

I'm just realizing now that it's not spelled "Wein", which maybe explains how I got it wrong all these years.

[@AnalogueGround]

Wee-en but only because I've heard that the most from engineers

[@whosonedphone]

The resistance is futile!

[@miguelmouta5372]

Sir, I would like to join in the National Sarcasm Society.

[@AmRadPodcast]

Anyone can be a member! -Derek

[@miguelmouta5372]

@@AmRadPodcast Thank You! 😆