Random-function troubleshooting

Pehr · Posted: Wed Mar 05, 2008 3:36 am Post subject: Random-function troubleshooting

I've just put in a fresh LM358 for the random-comparator (I didn't have on before) and I've started playing around with the random input ets.

Of course it is behaving a bit odd... Rolling Eyes

The random level pot does not seem to work at all.
The random reference seems to work in a very small interval in teh lower end of the pot.

In other words, a change of 1mm means comparator always on or off...

If I'm really lucke I can get a random sequence...

What could be wrong? I've replaced the 100 k pots with 50k ones but no diff... Crying or Very sad

Scott Stites · Posted: Wed Mar 05, 2008 7:15 am Post subject:

Hey Pehr,

What are you using as a random input? IE, that sounds like what you'll get if there is no signal applied to the random input or the random signal isn't making it from the input to the LM358.

Cheerio,
Scott

Pehr · Posted: Wed Mar 05, 2008 10:50 pm Post subject:

Hmm, good point. I havent tested if the signal gets through yet.

I've tried:

White noise
Pink noise
Gate 3 output
sine wave from a VCO
sine from LFO
Saw fromLFO

All with the same result, so I think I'll see if I get a signal at all.

Thanks!

brgds
- Pehr

Scott Stites · Posted: Thu Mar 06, 2008 7:27 am Post subject:

Righto - the signal should go to the anode of D4, then through D4 to pin 3 of U8 (the LM358). So, the signal has to be a bit higher than 0.6V or so to register, which I imagine the signals you describe more than acquire.

R94 (100K) connects between Pin 3 of U8 and ground, which provides the input impedance required for the the thing to work. The diode just keeps negative voltages from coming through.

Pin 2 of U8 should reflect the reference voltage as dialed up by your reference pot - I think that's fine, judging by the fact your LED comes on at the extreme setting, but it doesn't hurt to check. Usually. Laughing

Let me know what you find, Pehr.

Cheers,
Scott

Pehr · Posted: Thu Mar 13, 2008 1:55 pm Post subject:

Everything seems to be in order... all components are connected correctly.

Next step is to do some measurements of voltages at some points.

Pehr · Posted: Thu Mar 20, 2008 11:17 pm Post subject:

Everything seems to be working fine. The comparator works properly.

I guess it depends on the signal I have fed into the random input. Smile