Super Simple Oscillator Questions Mega-Thread

Hi, I hope everyone doesn’t mind but I wanted to make one catch-all thread for a bunch of questions I’m having about this circuit. As well as inviting others to ask anything they might be curious about. So with that being said here goes!

For the sake of being simple, I’m going to ask one question at a time, get the answer, and then move on to following questions.

First, Sam has a 10k linear pot in his video. What would larger or smaller values do? And what would happen if I used logarithmic pots instead? I’m trying to save myself the headache of buying parts I don’t need.

Thanks in advance for the help!

The pot setting changes the frequency, but the range is limited. Depending on the transistor, the oscillator may stop at some pot setting. So a smaller pot may work fine, or might give a smaller frequency range. Offhand I don’t remember if the oscillator stops at too high or too low a resistance, if too low you might need a larger fixed resistor in series with the pot. A larger pot will probably not give a larger range, and the usable range will be a smaller fraction of the total pot settings. So a larger pot is probably not a great idea though if 20k or 50k is all you have it might work well enough to get started. A log pot will give a different kind of response, slower change of frequency at one end and faster change at the other end than with a linear pot. It’ll work, you might prefer one over the other.

2 Likes

Sick thank you.

Speaking of in Sam’s video he has it where when the knob is fully counter-clockwise(at “zero”), the oscillator is off. And then increases in pitch as its turned clockwise. Mine is functioning at “zero”, increases in pitch, and then stops making sound at fully clockwise (“ten”). Why is that? I’d prefer if it worked like his does. If it helps, im using a different transistor as well. A SS9018, since it runs off 9v.

1 Like

Maybe invert the pin of the pot :wink:

EDIT : if it increase “normaly” that’s don’t work sorry

Try increasing the fixed resistor? If it’s increasing in pitch as you turn it CW that means it’s connected such that the resistance is maximum when fully CCW, so increasing the resistor will make it “more CCW”.

its currently decreasing in pitch as i turn the knob clockwise. i did get it fixed that all the way counter-clockwise is off though. but as i turn it clockwise, it starts at its highest pitch and gets lower in pitch as the knob is turned more clockwise.

So reverse the pot connections.

1 Like

alright bear with me cause this is probably a dumb question, but do you mean reverse lugs 1 and 3?
i did that just now, and it moves up in pitch correctly (more clockwise = higher pitch), but now its completely off when its at 10.

Which is what I thought you initially described; I suggest increasing the fixed resistor.

2 Likes

ok before i try that, mostly cause i only have 1k and 100k resistors right now lol, i want to just try mimicking whats in the video. i have like 10x over checked my work to make sure i copied the layout correctly, it SHOULD work the same. i cannot figure out why its acting differently for the life of me. its really doing my head in!

at the timestamp you can see it working as intended, mine is not sadly :frowning:

You said you’re using a different type of transistor and a different voltage. Besides that, this circuit uses the transistor in a way transistors are not intended to be used. So the behavior is not guaranteed. Not only will different transistor types behave differently, even the same type from different manufacturers may, and possibly even two transistors of the same type from the same manufacturer in the same batch.

Get more resistors. For $6 you can get 600 resistors of 30 values.

4 Likes

i figured it out. in some of the references, the cap is one way, and in other references its the other way. i literally had the cap backwards because i was referencing the layout on the LMCN project page, but in the video the + and - are reversed. so there you go, thats problem is solved.

The + side has to connect to the pot and the - side to ground, as shown:

image

1 Like

heres the layout shown in the 1st video, as well as the beginning of the 2nd video(cause theyre the same image ofc).

thank you for the link to the resistor variety pack btw, definitely going to pick that up.

1 Like

good news. i got the oscillator to behave the way i want with a purple LED. the red, orange, yellow, green, and blue LED’s i have all behaved “incorrectly”. so now i just need to figure out why!

1 Like

Nice.

Do you have any details or a link to this purple LED, I would be interested to know what is the reason for the difference.

Presumably an effect of different forward voltages. Which I guess means the cap has to charge to a different voltage before the avalanche effect occurs. <waves hands vigorously>

6 Likes

That was my guess as well, but am still interested in finding out.