Thanks for the generous replies everyone . . . much appreciated. I will verify the circuit ideas and post the results . . . I'm waiting on an order from DigiKey . . . I thought I had some spare op amps in the junk-box, so it will be a few days . . . I ordered some true rail-rail devices by Microchip.

-Mike

 

A conventional UJT circuit will give a sawtooth waveform (i.e slow rise sudden fall), not a symmetrical triangle.

Yeah, I'm familiar with the classic single UJT sawtooth/ramp oscillators ( I think they're referred to as "relaxation" oscillators) . There are many examples in some of my reference books . . . My bad - I tend to use sawtooth/ramp and triangle interchangeably (old habit) when I really mean "triangle" . . . .

 

DickCappels -

Thanks . . . . I'll keep that in mind . .

 

Using LM358:

Circuit in #3 results in no change, other that slight reduction in amplitude.

Circuit in #6 produces a distorted waveform . . . DC level came down only by a fraction.

Tinkered around with both of these circuits, using the MCP6002 also. Pretty much the same results.

The original circuit using a MCP6002 works pretty much how I want. The output swings about 200mV above ground. If I fiddle slightly with the
voltage divider feeding pins 3 and 6 I can bring it down to about 50mV. Followed by a output level pot I can bring in down to 0v, so I get a nice stable triangle wave that swings between 0V and +2V.

It's a great little chip at about .60 cents! My first experience working with these newer op-amps and they win hands down! It will run on as little as 1.8V and has much better specs than anything else I've worked with over the years.