[sdiy] Newbie needs help with VCO

[Grant Richter]

One thing to remember is the LM311 has an open collector output. The
resistor pulls it up to ground. So the output of the LM311 should be at -15
volts, with very brief pulses to ground. If the gate of the FET is not at
-15 then the cap will not charge at all.

So you can watch the output of the CA3140 and tell something about the
problem.

Output at +15 = current source works, problem with LM311 or FET
Output at ground = current source not working or FET always on
Output at -15 volts = a wiring error since it does not go negative during
normal operation
> 
> The LM311 is connected up correctly, as far as the diagram goes.
> There is some detail missing, that, if you are not familiar with the
> LM311, you might not know about.  If you have the time to download
> this:http://www.silcom.com/~patchell/smb1/smb.pdf, there is a schematic
> of basically the same VCO, that shows all of the LM311 pins and where
> they need to go.  Unfortunately, the VCO is on the last page of about  24
> pages.....I remember the first time I used the LM311....I couldn't get
> that sucker to work at all....then I put my glasses on and realized what
> I thought was an 8 was a 3 :-).....or something like that....well, that's
> my story, and I am sticking to it.