Crude sawtooth generator - would this work?

[EarlOfWessex]

Hello, first post for me. I've looked everywhere, and have found nothing.

Ok, so the theory goes...

the relay is closed, charges the capacitor, and removes the potential across the relay, opening it.

the capacitor discharges at a speed controlled by the pot, until its low enough to trigger the relay, the process is repeated.

the coil would see a sawtooth wave, with both positive and negative swing (because of the resistor to ground), with the speed controlled by the pot.

I know that any relay would burnout quickly, and for even low frequency waves I would need to use something else.
but would this work in theory?

the goal of this is to produce a variable horizontal sweep for an oscilloscope.
I have ripped apart an old CRT monitor, because I can't afford a real scope.

I know the wave slope wont be straight, but I don't think it will matter, as long as its consistent.

Thanks for taking the time to read this.

 

[reese]

It looks overly complicated. Try this simple circuit using two op-amps.

**broken link removed**

 

[Willbe]

Hello, first post for me. I've looked everywhere, and have found nothing.

Ok, so the theory goes...

the relay is closed, charges the capacitor, and removes the potential across the relay, opening it.

the capacitor discharges at a speed controlled by the pot, until its low enough to trigger the relay, the process is repeated.

the coil would see a sawtooth wave, with both positive and negative swing (because of the resistor to ground), with the speed controlled by the pot.

I know that any relay would burnout quickly, and for even low frequency waves I would need to use something else.
but would this work in theory?

the goal of this is to produce a variable horizontal sweep for an oscilloscope.
I have ripped apart an old CRT monitor, because I can't afford a real scope.

I know the wave slope wont be straight, but I don't think it will matter, as long as its consistent.

Thanks for taking the time to read this.

Depending on your voltages and how much current you need to source, how 'bout a neon bulb, a resistor, and a capacitor? The sawtooth peak voltage would be about 65vdc.

 

[EarlOfWessex]

how would that all fit together?

I'm trying to learn about op amps in order to build the circuit suggested by Reese, and then to amplify the output with a couple of power transistors I've ripped from a broken PA. but due to time and money constraints I've been extremely slow progressing so far...

to be honest, I'm a little confused about the current and voltage I need to draw,
I think that my CheapDMM is playing games with me.

 

[Willbe]

how would that all fit together?
I think that my CheapDMM is playing games with me.

If you mean my parts list, the neon goes across the capacitor, and this parallel assembly is in series with a resistor and the source DC voltage.
When the voltage built up across the capacitor reaches approximately 65vdc the neon fires and discharges the cap to some low voltage.
Then the cycle begins again.
It couldn't be simpler. Theoretically the cap discharges infinite current so you might want to put a small resistor in series with the neon to protect it.

Or you could use a unijunction transistor circuit, if they still make unijunctions.
Or a diac instead of the neon bulb.

What are your DMM symptoms? Usually they are pretty hardy but there are several ways to get weird readings.

 

[Willbe]

how would that all fit together?
I think that my CheapDMM is playing games with me.

Usually for Top Down Design, we should start at the desired output voltage/current and work backwards from there.

But, if you mean my parts list, the neon goes across the capacitor, and this parallel assembly is in series with a resistor and the source DC voltage.
When the voltage built up across the capacitor reaches approximately 65vdc the neon fires and discharges the cap to some low voltage.
Then the cycle begins again.
It couldn't be simpler. Theoretically the cap discharges infinite current so you might want to put a small resistor in series with the neon to protect it.

Or you could use a unijunction transistor circuit, if they still make unijunctions.
Or a diac instead of the neon bulb.

What are your DMM symptoms? Usually they are pretty hardy but there are several ways to get weird readings.

 

[audioguru]

Remember a Unijunction Transistor? Or a PUT (programmable unijunction transistor?
They made pretty good sawtooth waveforms a long time ago.

 

[em2006]

Remember a Unijunction Transistor?...

Oh, I like it!

 

[Hero999]

What frequency do you require?

Does it matter?

You could use a reverse bias oscillator.
**broken link removed**
**broken link removed**