XR2207 and XR2209 VCO chips

[Rene Schmitz]

At 11:18 27.01.99 -0800, you wrote:

>Secondly, they have linear frequency sweeps.  So 1V/oct. operation is out
>(this is considered the biggest stumbling block).

The same is said for the LM566 (tri, square), but there are ways.
I don't know exactly for the 2206, but it could be done similar:

The pin for the timing resistor really senses the current into (or out of)
that pin, (i.e. the pin is held internally at some voltage and the current
flows to ground, or the control voltage) so it is misusable as a current
input, with the usual expo convertors.

See http://www.uni-bonn.de/~uzs159/vco_566.html 
for an example.

It *may* work similarly for the 2206, when pin 9 is left open and a current
sinking expo convertor is connected to pin 8. pin 8 is held at 3V above
ground. I have not tried it, but If I had some 2206s around I'd certainly
try it. I did build the circuit on my website however, and the sweep range
is more than sufficient (app. 1:10000 !) though the datasheet claims only
1:10, but this figure is only for voltage control in the normal
applications, and with a resistor as current source!
This VCO did track pretty good, for such a cheap thing.

Bye
 Rene








I could imagine that similar sweep ranges can be archeived with the 2206,
too. 


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