Troubleshooting triangle oscillator

I recently assembled this schematic on a breadboard:


the circuit is powered by a 9v battery and I also have an LED connected between the output and ground and the 100k resistor is replaced by a 100k potentiometer. I have used two different op-amps in the circuit and each seems to have different problems, when using a 4558 the led stays on all the time and does not oscillate at all, when I use a tl072 the led stays off all the time also with no oscillation. Here a picture of my circuit with the 4558:


I can't seem to figure out why my circuit doesn't work, could it be that I need a bipolar power supply? If so is there a way to modify the circuit to work on a single pole?

I designed the circuit using this web-app:

https://www.falstad.com/circuit/e-triangle.html

That circuit is intended for a bipolar supply, but you can easily modify it to work with a single 9V battery.

Just connect two 10K resistors in series between the + and - terminals of the battery. The mid-point of the two resistors is your new "ground". So the two opamp inputs that are shown as connected to ground should be connected there instead of to battery - (or wherever they were connected). The actual values of the resistors doesn't really matter so long as they're the same.

The LED should still be connected between one of the opamp outputs and one of the battery terminals, but it should have a resistor (e.g. 1K) in series with it.

- - - Updated - - -

btw, with the values shown, the LED will flash about 40 times per second. To slow it down, you need to increase the value of the capacitor and/or the 100K resistor.

after following your advice (albeit with 22k resistors instead of 10) I now get the same result with the tl072 that i do with the 4558 only it still doesn't oscillate. I also changed the 100k resistor for 500k. could I be missing something else?

Are you sure it's not oscillating? If the LED's flickering at 40Hz,that's probably too fast for you to see. To the eye, it will look like a continuous glow. Try increasing the capacitor to 1uF (or more) to slow it down.

I upped the 100k resistor to 500k and still get nothing.

Did you put a resistor in series with the LED?

The breadboard circuit doesn't correspond to the schematic, it has even unconnected OP pins. Please show the schematic you want to implement.

godfreyl said:

Did you put a resistor in series with the LED?

Click to expand...

Miraculously after this step it seems to work properly