# Simple square wave frequency multiplier/divider

I have a square wave 0-12 V input signal that varies from 30-150 Hz, which I wish to multiply to an output square wave 0-12 V signal of 60-300 Hz. In this case, the multiplier is 2, however I ideally need this to be adjustable as I am not sure exactly what it needs to be — it could be anywhere from 1.6-2.4, but will not need to be changed once the correct value is found.

Is there an IC, or circuit, that can be made using simple components to achieve this, where changing the value of one component alters the multiplier?

Given that the multiplier is not necessarily an integer, it sounds like a tiny MCU would be the best solution. Its simple program would measure the period of the incoming signal and synthesize a new signal that has the computed new period.

You would need a small regulator to power the MCU, and simple circuits on the input and output to handle the 12 V signals. The internal clock of the MCU would be fine for this — its absolute accuracy doesn't matter; only its short-term stability is important.

• By MCU do you mean something like an Arduino? If so, is there a software library that you would recommend, or a specific MCU Commented Jul 21 at 21:17
• An Arduino woud be way overkill for this, but sure, if this is a one-off project or you just want to prove the concept, it would be fine. I was thinking more along the lines of an ATtiny412 or -212. I am used to doing my own low-level programming on MCUs, so I don't tend to think in terms of libraries. Look for ones that deal with the hardware timers. Commented Jul 22 at 11:38

It would be possible to do this with a CMOS PLL such as 4046 and a divider plus a programmable divider.

For example, suppose you lock onto 256 times the input frequency (8 bit divider) so you have 7.68kHz to 38.4kHz.

You could then divide the higher frequency, for example a 100Hz input would give a VCO frequency of 25.6kHz and dividing it by 512 would give you 50Hz (divide by 2), by 511 would give you divide by 1.996 etc. 4000-series CMOS can also operate directly at 12V.

However this would take a small handful of CMOS chips and I think, even with level shifting considered, Dave's answer is the one I'd actually choose.