I created a thread about this a while ago and back then i did manage to get a working circuit. Looking back at it now I'm still not very happy with it so i decided to give it another shot, and because you're reading this i obviously failed.
The idea is to create a square wave oscillator where the frequency is adjustable using a potentiometer.
Some things I took into consideration:
I have, of course, been spending lots and lots of time trying to get a working circuit myself, these are some of my attempts:
Thanks for taking the time to read my post.
The idea is to create a square wave oscillator where the frequency is adjustable using a potentiometer.
Some things I took into consideration:
- I could use a 555, op-amp, Schmitt trigger, or whatever IC to create this circuit, but these come with a lot of extra fluff that isn't required for a working oscillator and because the rest of the project is built from scratch, without ICs, I also want to build the timing circuit from scratch.
- The circuit must have actual outputs. High is V+ (5v) and low is V- (0v), not some internal state change where the circuitry to read the output affects the oscillation frequency or duty cycle.
- The output load must never affect the frequency or duty cycle.
I have, of course, been spending lots and lots of time trying to get a working circuit myself, these are some of my attempts:
- The standard astable multivibrator circuit:
https://upload.wikimedia.org/wikipe...r.svg/1280px-Transistor_Multivibrator.svg.png
The basic astable multivibrator has two issues: It's more of a saw-tooth wave than a square wave, and it has two frequency determining networks so a potentiometer can't be used to adjust the frequency.
There are many different variations on the basic circuit which solve some of these issues but I still couldn't find any that fit all requirements. - The Schmitt trigger relaxation oscillator:
https://upload.wikimedia.org/wikipe...80px-Schmitt_trigger_with_transistors.svg.png
https://upload.wikimedia.org/wikipedia/commons/7/7a/SchmittTriggerRelaxationOscillator.png
My last post was about this circuit, using a Schmitt trigger IC this oscillator is perfect for my needs, but the transistor Schmitt trigger shown above is nowhere near perfect and suffers from these issues: There's tons of calculations online about determining the low and high threshold of the transistor Schmitt trigger, some different than others, which are correct? I don't know, none of them matched the behavior i got after building the circuit, and the output low isn't actually 0 volts but the result of the resistor voltage divider Rc2 and Re, the output load also affects the frequency. - My own attempts:
I suck at designing circuits, no wonder none of them worked.
Though i did learn a lot in the process.
Thanks for taking the time to read my post.