I have this inverting Op Amp circuit. When I input a TTL signal which goes from 0 to +5 volts, I expect the output to be inverted and go from 0 t0 -9 volts.
What I see on the O'scope is a square wave going from +9 volts to -9 volts.
Do you know how to calculate the gain of your circuit? It appears to be more than ten times what you want.
Also by capacitive coupling the input you change the signal from 0 to +5V to +/- 2.5V (the capacitor blocks the average DC voltage of the signal, look at the output of C1), thus the output will also be plus and minus (but inverted), not zero to minus.
Why do you have such an elaborate filter on the 9V to the input?
The gain is high because this part of a larger circuit. A microphone is actually attached to the input. I was just testing the circuit with the TTL signal.
Audioguru is correct this opamp is not rail to rail. I was just being lazy by writing +/- 9 volts rather than several volts below the rail voltage.
A microphone is actually attached to the input. I was just testing the circuit with the TTL signal.
I was just being lazy by writing +/- 9 volts rather than several volts below the rail voltage.
One of the joys here on ETO is finding out what the REAL QUESTION should have been.
It usually takes a few more iterations than this. Well done.
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The 2.2k resistor for powering the Jfet inside an electret mic has a value too low so it loads down the signal level from the mic. Use 10k.
The opamp is inverting with an input resistance of only 10k which also loads down the signal level from the mic. Use a non-inverting circuit with an input resistance of 50k.
The high value of the 10uF input capacitor C1 is silly because it passes earthquake frequencies as low as 1.6Hz.