# XR2206 faulty I.C?

Discussion in 'The Projects Forum' started by Neil Groves, Sep 28, 2013.

1. ### Neil Groves Thread Starter Member

Sep 14, 2011
125
3
Hi guys

I am building a function generator based around the above I.C, I have got a wonderfully clean square wave but when I vary the voltage on pin 3 to adjust the amplitude, nothing happens.

just for test purposes I have a pot one end on 12V, one end on 0V and the wiper going direct to pin 3 of the device, the voltage on pin 3 varies as I would expect on pin 3, but the output of my square wave stays constant, I am wondering if I might have a faulty chip?

Neil.

2. ### MrChips Moderator

Oct 2, 2009
18,154
5,700
It might help if you provided us with the complete circuit diagram.

Apr 5, 2008
19,265
3,887
Hello,

You are not supposed to connect a potmeter between 0 and +12 Volts on pin 3.

The pin 3 is for adjusting the output voltage of the sinewave and triangle.
It will do nothing on the squarewave.

Bertus

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4. ### Neil Groves Thread Starter Member

Sep 14, 2011
125
3
I am just configuring it that way for test purposes Bertus.

ok I will experiment with the other waveforms and see what happens.

thanks

Neil.

5. ### Neil Groves Thread Starter Member

Sep 14, 2011
125
3
ok just checked things out and yes the sinewave output (pin2) responds nicely to voltage applied at pin 3, BUT.....the peak to peak of the sinewave itself doesn't adjust, only the D.C level on which it sits varies?

Neil.

6. ### Neil Groves Thread Starter Member

Sep 14, 2011
125
3
So how can I get the bottom of the sinewave to sit at 0V? if I add a cap in series with the output the sinewave straddles the 0V rail. being equally above and below......or is this how it is supposed to be?

7. ### MrChips Moderator

Oct 2, 2009
18,154
5,700
If you put a cap in series that is called a DC blocking capacitor, i.e. it blocks the DC.

In other words it makes the average voltage zero.

That is what a DC blocking capacitor is supposed to do. It would make a perfect sine wave straddle 0V.

8. ### Neil Groves Thread Starter Member

Sep 14, 2011
125
3
Great, it's all working then, thanks everyone for your help.

Neil.