Hi, I am trying to make a simple Op-Amp Buffer with a TL072, but failing miserably and things are happening that I don't understand. I've attached an image of the circuit.
Basically I have an external variable resistor (big piece of carbon) that ranges between 500KOhm and 1500KOhm when agitated. I then convert this to a voltage using a divider and end up with a voltage between 3V and 6V at the Test Point pictured on the switch. This is the goal voltage.
The weird thing I don't understand is that when I connect the switch to the non-inverting input of the TL072 that point's voltage gets fixed at around 8V, even when I vary my external resistor. Also this 8V voltage is reflected at the output of the OpAmp. How do I make it so the 3V-5V I am getting at the Test Point are reflected at the output of the buffer.
I realize the TL072 needs a bipolar supply and I've tried adding a voltage divider consisting of 2 100K resistors at the non-inverting input, but that didn't seem to fix anything.
Thanks for any direction.
Basically I have an external variable resistor (big piece of carbon) that ranges between 500KOhm and 1500KOhm when agitated. I then convert this to a voltage using a divider and end up with a voltage between 3V and 6V at the Test Point pictured on the switch. This is the goal voltage.
The weird thing I don't understand is that when I connect the switch to the non-inverting input of the TL072 that point's voltage gets fixed at around 8V, even when I vary my external resistor. Also this 8V voltage is reflected at the output of the OpAmp. How do I make it so the 3V-5V I am getting at the Test Point are reflected at the output of the buffer.
I realize the TL072 needs a bipolar supply and I've tried adding a voltage divider consisting of 2 100K resistors at the non-inverting input, but that didn't seem to fix anything.
Thanks for any direction.
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