I just wanted to say thank you for the responses so far.
I think a micro-controller isn't doable for me because I don't have a programmer. I did save the article though. Maybe I can build one sometime.
The other two options may be more helpful to me. But this brings a couple more questions to mind that maybe you can let me know if I am clear on.
The 555 timer circuit that I built has a 1K - 20K (pot) - 1K resistor in series from Vs (5v) to the positive side of 5 capacitors in parallel (0.01uF, 0.1uF, 1uF, 10uF and 100uF) the other end is switched to ground to select a range of frequencies for the output. The 20K potentiometer gives a way to adjust the frequency band for a selected capacitor.
So am I right in the following statement:
Maximum current when a fully discharged capacitor is switched to ground will be 5V / 22k ohms = 0.000227273 A or roughly 227uA
Given that, I should be able to source the current with just about any TTL chip, correct?
When I tried that, looking at the output of the 555, (if I remember correctly) had some sort of sine wave embedded on the clock signal. My test was using a 2-input NAND (7400) gate with one input wired high and the other input wired to a switch. The output of the NAND was wired to the negative lead of the capacitor. When I send a HI to the second input of the NAND and get a LOW on the output, I would expect the chip to sink the charge current of the capacitor. I think the capacitor discharging is what was messing up my signal. (I really don't know).
My next try was to use a 2N3904 (or equivalent) The output of the gate went to a resistor. The other end of the resistor went to the base. I also added a resistor from the base to ground. Emitter was connected to ground and the capacitor was connected to the negative lead of the capacitor. When the BJT was turned on, I had basically the same problem as just using the gate.
Isn't this last example an Open Collector out? Would using a gate with an OC out be any different?
Perhaps I done something wrong in my experiments. I will go to the proto-board and try again. This time I will capture some of the waveforms with my scope of the outputs and attach them so you can see what I am seeing.
Again, from your suggestions, it sounds like I should be able to switch the caps to ground pretty easily.
Thanks for your suggestions and patience with this old newbie!
Regards,
Joe