Variable frequency 555 circuit

Does something here help?

Not really practical, sorry.

The 555 is basically two comparators and an SR latch. The output toggles low when the high threshold input is reached, and high when the input drops below the low threshold.

The charge/discharge time to reach the high or low thresholds is totally dependant on the external components.

The only internal "variable" is by changing the bias voltage on the resistor divider that the comparators use for the thresholds; the upper comparator point in the divider is brought out on pin 5.

That allows some change in frequency but at a guess possibly 4:1 or so, not 1000:1
The control voltage is not linear.

555 internal schematic:




To actually use a 555 over that 1000:1 range, you would need to select different external components using a bank of analog switches, each giving that 4:1 range, so six or seven ranges, each range individually calibrated and with logic to switch between them. It's very unlikely it would ever be long term stable, even if you could get it to work initially.


To get the type of frequency range with complex external switching using analog parts takes such as a purpose made voltage controlled oscillator or such as the VCO designs for modular music synthesisers.


A single MCU could do the whole lot far more accurately with minimal components.

And, as you want to control it via an internet connection, you would need an MCU to do that. The audio could be generated directly in the same device.

What accuracy do you need of waveform parameter control,
freq, duty cycle, etc... Do you need burst sine, arbitrary, tri, saw....?

Something like this, one chip :


Regards, Dana.

If you have a pot =>100k the max/min ratio value on tap may exceed 200:1: then a simple RC logic Astable Osc will give this f ratio. The are 2 types: a) Schmitt inverter b) dual inverter with 2 R’s, 1C.
The a) method can also be a CMOS OpAmp with single or bipolar supplies using any R ratio hysteresis (+in) and self biased (-in) RC.

Search _____ and you wil find it easily.