I'm into building synthesizers from scratch. I've recently built a low frequency oscillator as part of an instrument which works well, based on a TL074 quad op amp. However, it uses a heck of a lot of components and is rather 'clunky' as it requires a great deal of switching to allow 4 different waveforms (rising saw, falling saw, triangle and square).

I've been trying to improve this circuit by cutting down the components required so it can fit on a smaller piece of stripboard.

I found this image on google, with no context or explanation. Caption says it's just 'an idea'.

CMOS Oscillator

I have several 4069 chips and would like to try it. Before I commit it to perfboard, can anyone tell me if this schematic will actually work? And if so, what will the P-P amplitude of the waveforms be?

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    \$\begingroup\$ Got a breadboard? Breadboarding is a lot less commitment than perfboard. \$\endgroup\$ – uint128_t Apr 12 '17 at 16:12
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    \$\begingroup\$ I've nothing technical to offer, just think it's brilliant that you're building your own synths :-) Presumably they're true analogue rather than digital/hybrid. \$\endgroup\$ – TonyM Apr 12 '17 at 20:26
  • \$\begingroup\$ The sine wave is only due to slew rate limiting of CMOS at max f \$\endgroup\$ – Sunnyskyguy EE75 Apr 12 '17 at 21:37
  • \$\begingroup\$ I managed to get this working in the end on breadboard, with a couple of adjustments. However, I forgot to write down the schematic and when I went to recreate it last night had totally forgotten what I did to make it work! I even added a potentiometer so I could blend between the triangle square wave, added an LED via 1k resistor to pin 4 to show rate, and omitted the sine output altogether. Now the LED just stays constantly lit and doesn't flash like it used to. I think maybe the resistor values 1M and 680k aren't quite right - I know in a hex schmitt they have to be roughly double. \$\endgroup\$ – TCassa May 25 '17 at 10:12

If you want an easy triangle square wave generator, your relaxation oscillator or this one to use. For a stable reference add 1 MHz Xtal and for really long time constants (2^14) add a CD4060 timer.

I did a quick and dirty design here using a log Pot with 4way cap selector with good tight wiring practice ;) in my SIM. enter image description here

Extra bits for misc. reasons.

  • Good Cap Decoupling is mandatory, Ground plane is desirable.
  • Then use twisted pair AWG 30 magnet wire for signal paths. (Poor man's coax)
  • Using a wideband low input current Op Amp to buffer the inverter input triangle wave out is OPtional (1/3 to 2/3 Vcc) and the unused Schmitt Inverters ganged for a buffer is a bonus.
  • You can change the Series R and Pot from 1M and any caps to choose 1 decade, 2 or 3 which is a practical limit. So with 3 Caps I spanned almost > 7 decades.

  • Choice of CMOS family is critical for max frequency and important for lower output impedance. 74ALCV being the lowest Z at 25 Ohms nom.

  • \$\begingroup\$ Thank you for this - I have to confess I don't understand a lot of it! It is a little advanced for me. Is that a 40106 chip? Also, where does that stray 1k resistor go to? \$\endgroup\$ – TCassa Apr 13 '17 at 8:13
  • \$\begingroup\$ DNI , NC , not needed yes 40106 is like 300 OHM 15V CD4xxx series <10MHz and ~ 1k RdsOn at 3V, if you need 15V ok, otherwise newer families for 5.5V max are lower impedance \$\endgroup\$ – Sunnyskyguy EE75 Apr 13 '17 at 12:29

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