Could anyone please post a circuit here that will provide a linear adjustment curve for the frequency control pot on an XR2206 function generator IC?
I recall seeing one but can't find it anywhere now.
Thank you,
Dennis Kent
Dennis, since the current out of Pin7 resp Pin8 is linear with frequency you could use a current sink instead of a resistor. f(Hz)=320*It(mA)/C(uF) The range can be from 1uA to 3mA. The compliance is around 3V. The current sink can be made with an opamp with a 1k sensing resistor driven by a pot from a 2.5V reference for example. If you use a logarithmic pot, you can get a respective curve.
2.5V pin7 o o | | .-. |\ ||-+ | |
This is very helpful. Excuse me for being dense, but what does the symbol below pin 7 represent.
Thanks,
Dennis
Looks like an N-channel enhancement mode MOSFET. But I think an NPN bipolar would work OK too.
It is a small N-Mosfet like VN1310N3 or BSS100, also a bipolar will work, but might need compensation to not oscillate. The Gate is left, the Drain goes to 7 and the Source to the resistor. The current is Vin/1k, so 2.5V will give you 2.5mA and 0.001V will result in 1uA. So a precision opamp should be chosen like TLC2201 if you need the full range.
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