I was going to say that but then I remembered this stripboard diagram doesn’t seem to jibe with what I remembered building. Compare with this: https://canada1.discourse-cdn.com/free1/uploads/lookmumnocomputer/optimized/2X/9/9de6b986759173c7c0bbd3f826086abdd577ce92_2_666x500.jpeg
Also see second stripboard layout and schematic at https://www.lookmumnocomputer.com/projects/#/simplest-oscillator
but in the schematic it looks like the transistor’s backwards? I dunno…
According to the stripboard though, the output should be coming from the collector side of the transistor.
But it looks like in this, the emitter is whats feeding the output.
Though to be fair, it worked for @richy486 with the inverse, so this prolly doesnt matter.
@SonOfAGlitch, whats the voltage in for the batteries, just checking that enough power is there. Can you check the rails on the breadboard?
In the second stripboard layout, it’s on the emitter. And that’s what I recall doing.
Yeah, i updated the post to show it works both ways.
So the way this works is that you are basically putting so much voltage on this transistor that it reaches it’s “Breakdown voltage”. This is the voltage which causes what is normally an insulator or semiconductor to become conductive.
Avalanche Transistors like the 2n3904 are designed to operate in this breakdown voltage region. This is called “avalanche mode operation”. This has the effect of generating fast pulses. When you reverse the connections to the collector and emitter, this is called a “reverse avalanche mode”. This version requires less voltage to get to this avalanche mode because of the asymmetry and doping differences between the emitter and collector junctions. The voltages this occurs is not consistent, and might be why you have to try multiple transistors before you find one that this phenomenon will occur.
This is whats happening in the circuit:
The capacitor is charged via the current limiting resistor (the 1k and the potentiometer). While voltage is low, there is not much current flowing between the collector and emitter, so lets just assume its not at all to simplify. When the capacitor is charged enough, the transistor will reach a point where it hits that “avalanche breakdown region”. In this mode, the transistor will have “negative resistance” (higher the current, lower the resistance) which will cause the capacitor to discharge rapidly though the LED. The frequency of which this process occurs is dependent on the resistor and capacitors chosen (look up RC time constant for more details), this is why the pitch is altered when you vary the resistance with the potentiometer, since it affects the frequency.
TLDR;
Try another transistor, it might work.
(nit: 2N3904 is a standard small signal transistor, an avalanche transistor would be a more specialized component like ZTX415).
Woops, my bad. Thanks for keeping the record straight.
Hey guys,
since I’m a bit lost, I checked some videos about basic oscillators, which have kind of the same circuit but without a potentiometer (link to video: https://www.youtube.com/watch?v=I-YANhpiUCQ). The video is showing how capacitors with different resistance affect the blinking of the LED (at some point he’s using a 2200 uF capacitor and the rate of the oscillation is so slow that we can see light pulses in the LED). Hence, I removed the pot (sending the signal directly from the 1k Ohm resistor to the capacitor and transistor) to see if that works for me as well: I put 2x 1k uF capacitors in series but I don’t notice any oscillation in the LED. I also tried again to switch the transistor the other way around (with the collector feeding the LED and the 100kOhm resistor) and noticed that the LED turns off. Do these two things mean something? Does anybody have a clue?
Capacitors add in parallel, not series, if you want something like that 2200 uF cap.
@analogoutput uh yeah sorry, that’s what I did (+ to + and - to - right?). The weird thing is that I read this topic How does one make blinky lights n such? and tried to build a super simple circuit to see te light pulses (without capacitors), just sticking there a 1k ohm resistor from V+, going into the positive leg of the LED, which is then going to V- with its negative leg (LED GLOWS STEADILY). I then tried to add the 2N3904 between the resistor and the LED with the same result as before. So, from the topic I read I understood that in the first circuit the LED shoul just be displaying the fact that the voltage is oscillating between + and - right? But in the case of the oscillator, it is the transistor that, hitting its breakdown voltage, will become conductive and the signal flow through. Now my question is: why can’ t I just remove the transistor using the voltage oscillation to make sound? The result of the very simple circuit that I was trying to do before (R+LED) seems to be answering to my question, but I don’t get things quite right 
you can’t make sound without the transistor
in fact it is not an osc so simple as it seems, a lot of people here are struggling to get there.
if this is your first project I would advise you to try to make an APC (Atari Punk Console), a small drone with two 555s (there is little chance that you will not make a sound) and come back to this projet later
or read again the advice of Caustic, re check with the diagram, will read the other thread which speaks about it (quoted above) and if you choose to do it with a 2N3904 do not forget to test several of them they are not all equal before the oscillation
good luck
I agree, do the atari punk. It should work, and you will get that rush from doing thing successfully so you wont feel like the poo poo.
Here is a guide!
Just need some 555 timer ICs. The rest you have shown to have. These are good to have on hand anyways!
It’s “super simple” as in super simple circuit, but if you’re new to electronics and have a somewhat fuzzy understanding of the basics, it’s easy to mess up and if you mess up the wrong way you’ll fry the transistor (I’ve posted this video before) and then you can spend all day checking everything over and over again without getting anywhere.
(I suspect you could improve the chances of newbie success by doing a step by step build guide, e.g. start by making sure you can get the LED to light up and regulate the intensity with the pot, measure voltages across resistor and LED with a multimeter to learn how to do that, then insert the cap and see what happens when you connect and disconnect the battery, connect a speaker and check that you can produce a click, and finally prepare and insert the transistor in parallel with the cap.)
@fredrik Hey, thanks for your time. In fact, that’ s exactly what I did. So, the LED glows and responds to the potentiometer (gets dimmer as resistance increases) and the proof that I didn’ t burn the transistor is that, without it or with it the wrong way around, the LED doesn’ t light up at all, so I assume that the signal is flowing through the transistor and going to the LED. The capacitor doesn’ t seem to be doing much, since I can remove it without the LED being changed; the capacitor negative leg is going to GND, while it’s positive leg is connected to the transistor’emitter
have you tried several transistors ?
@Dud I did try a couple of different transistors; after checking the template on Kerry Wong site, I selected which one I had and tried them out but nothing. I also used all the 2N9304 that I have at home (about 20 pcs) without a good result, even though the LED always turns up when the resistor is connected and doesn’ t when it’ s not.
have you check your output on the collector with 100k like Caustic said ?
with what you try to listen it ?
maybe you have blown your transistors by turning them the wrong way
otherwise mine with 2N3904 started to oscillate at 20V, at 18 nothing, if you have done a lot of testing maybe take new batteries again
maybe you don’t have enough V for the transistors you have
another thing sometime the breadboard can become deffective, maybe try with other hole
can you re post a global pic plz
on your pic the OUT with resistor 100k seem not in a good place
the out (the resistor with your green wire with cocodile) must go to the collector (on the same ligne of the led)
