Created by
Created November 12, 2012
Last modified March 19, 2015
Tags 7555   oscillator   vco  


arduino controllable 7555 astable oscillator.


This circuit is a vco built on the 7555 timer in the astable oscillator configuration. The Arduino can control this circuit via PWM. One could also control the circuit by connecting a potentiometer wiper to the node where Arduino pwm is labeled.

If working with Arduino keep the vcc to 5v. If working with Teensy, use the voltage from the teensy to power the 7555.

if not using the Arduino to gate the circuit, connect the reset pin too VCC.

Please note that speaker or audio connections need to share ground with this circuit. (connect speaker to the circuit before R3).

Please see comment below by @signality regarding swapping out 7555 vs LM555 and so on.


I tried to create this circuit with a LM555CN timer with strange behaviors: on values above 127 the pitch is going to get deeper. i wont get any "good" pitches/notes. Is it because I use the LM555 instead of the 7555?

by madias
January 12, 2013

Hi Madias, I am note sure if the LM555 would be the issue or not. I have found that different 555s are more or less sensitive to the noise in the PWM. You may need to add capacitors to "decouple" the VCC going into the 7555 from the arduino. Hope this helps, Langdon

by langsound
January 14, 2013

Thank you! Problem (maybe) solved, have a look at this schematic: and use this in front of CV input. works like a rock, but i´ve tried it out with a different 555 osc building, your layout was "deconstructed"...I need more breadboards :)

by madias
January 14, 2013

indeed, an active (and tuned) lowpass filter will work much much better than this passive RC circuit. keep on rockin!

by langsound
January 14, 2013


There are several important differences between the 7555 CMOS and the original 555 bipolar timers.

i) the internal resistor ladder that sets the 2/3 and 1/3 switching points - and therefore the resistance presented at the CONTROL VOLTAGE pin - is much higher resistance in the 7555 (approx 100k vs. approx 5k per resistor).

ii) there is much less "shoot-through" current in the output stage of the 7555 than in the 555 (approx 2mA vs. 200mA). This makes the 7555 less dependent on having good supply and CONTROL VOLTAGE pin decoupling to avoid self triggering and cross triggering in multiple timer circuits.

There are good datasheets with some of this info here:

And some interesting background and alternatives here:

Sadly the ZSCT1555 is discontinued and Diodes Inc, who took over Zetex, now only make a clone of the original bipolar 555.

And this free book by the Hans Camenzind, late designer of the original 555 and the ZSCT1555, is absolutely priceless:


by signality
March 19, 2015

Thanks @signality!

by langsound
March 19, 2015

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