Waveform Generator - square and triangle

175

04:03:15

With variable frequency and voltage using the two potentiometer (500k in middle does frequency,  1k at bottom right does output voltage).  

The switch at bottom right switches between triangle and square waves.

Important:  Measure the waveform output at at the "watched" green waveform, above the 10k resistor at the top right of the circuit.  This is where the triangle and square waveforms are supposed to appear. Update: I’ve put a voltmeter component there and it is visualised on the graph. 

Based on https://www.jaycar.com.au/medias/sys_master/hff/h39/8884453310494/BJ8505-ShortCircuits-3-310316.pdf Short Circuits Volume 3, Project 30.

published 8 years ago

tcab

8 years ago

Status: Partially works. 1. I'm getting something like a square wave but its not square. 2. Triangle wave doesn't work when I flick the bottom right switch. Not sure why. 3. Frequency range of pot (500k middle pot) seems to give me a couple of values, not the entire range.

tcab

8 years ago

I've built this circuit in hardware and it works. The pdf instructions above offer useful debugging instructions e.g. 555 trig should be a triangle, 555 out should be square - verified true on my hardware version, but not so on this, my EveryCircuit version. I suspect it might be the EveryCircuit diode or transistor components which don't match the real hardware component specs?

hurz

8 years ago

A simulator can only as good as the information given to him! Would you please check again the Schematics, which is definitive not whats on your breadboard.

2ctiby

8 years ago

Adjusted here http://everycircuit.com/circuit/6009211680194560

hurz

8 years ago

The student didn't learned anything, cuz Mr GuessMess thinks he must appear and look clever.

tcab

8 years ago

@2ctiby - thank you so much - as you found, I had forgotten the ground on the 10nF capacitor coming out of 555 trig. And lowering the resistor beneath the LED used as a power indicator makes it light up nicely. Schematic now updated and working. Note: When I mentioned the debugging advice that "trig output of the 555 should always be a triangle" - see now that it is: the blue waveform shows a triangle no matter whether you are in 'square' or 'triangle' mode.

tcab

8 years ago

One remaining quirk in this circuit is that the 500K frequency POT in the middle has to be set to at least 93% for the triangle waveform to even appear. Not much frequency adjustment possible! The square wave mode is more resilient.

tcab

8 years ago

I played with changing the frequency POT (in the middle of the schematic) to 40K and that fixes the issue - but am wondering why I would need to depart from the original schematic 500K value so much? Possibly the transistor specs are involved (tweaking the EveryCircuit transistor specs helps a little but is not a clear solution like the POT drop to 40K is). Anyone have any thoughts?

hurz

8 years ago

And next time you probably better suspect whats obvious, a mistake in your work and not a dubious mistake in EveryCircuit.

tcab

8 years ago

I've gone ahead and changed the frequency POT (in the middle of the schematic) to 40K - just a trial and error solution as the original 500K from the schematic is not ideal. This now makes the circuit behave better re triangle waveforms.

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