_[sdiy]_ICL8038 worst ic off all time!

[Tim Stinchcombe]

> >As I recall it, in the 4046 you have basically two inputs and one of 
> >them is really a current input, so that's your entry into 
> the world. I 
> >did exchange emails with Björn Juhlin back then, and I don't recall 
> >exactly but I think I helped him with that particular part (I might 
> >have just caused confusion, since I was a little hasty to analyse 
> >things and made a few errors where he was right as I recall it).
> 
> Hmm, I'd still like to get this working.  Yes, you're right, 
> one pin (12?) is a 
> current sink pin.  I've designed a standard linear v-i 
> converter that sinks to 
> ground, but again, I think I was trying to run the current up 
> too high.  The 
> idea was to allow the v-i converter to control the current by 
> setting the 4046 
> VCO CV input to the positive rail (thereby opening it up 
> full) and let the 
> external sink do the work.  I'll have to try this again, but 
> be more mindfull 
> of the control current.

This works OK for me - I've been using the 4046 VCO to drive a
switched-capacitor filter lash-up. With a 100p cap between pins 6 & 7, pin 9
to supply, pin 12 open and pin 11 to a simple expo converter made with a
couple of BC547's, it is easily giving me up to 1MHz (although the waveform
is a little out of shape at high frequencies). I think I just figured the
max current from one of the charts on the datasheet. It doesn't track
1V/octave very well (I didn't try very hard), so no idea if it can be made
to do so easily. A book I have says problems with the chip are stability,
especially with respect to deviations in supply, and the variation from
device to device.

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk