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Linear Freq Ctrl for XR2206

D

Dennis Kent

Jan 1, 1970
0
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
 
B

Ban

Jan 1, 1970
0
Dennis said:
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, 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
| |
.-. |\ ||-+
| |<-------|+\ ||<-
| | | >--||-+
'-' .-|-/ |
| | |/ |
=== | |
GND '----------o
|
single supply opamp |
.-.
1k| |
| |
'-'
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
 
D

Dennis Kent

Jan 1, 1970
0
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.

This is very helpful. Excuse me for being dense, but what does the
symbol below pin 7 represent.

Thanks,

Dennis
 
B

Ban

Jan 1, 1970
0
Dennis said:
This is very helpful. Excuse me for being dense, but what does the
symbol below pin 7 represent.

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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