possibly a simple problem!

[lumley32]

right first post, i have some electronics knowledge and have done some work with IC's

long story short, i have a 0-12V square wave signal varying from 20-500hz, and i need to double the frequency.

it could be dropped to 5V in the process if that's any easer

i have looked at frequency multipliers online but they all seam to be far to high frequency.

any ideas would be welcome!

 

[john monks]

One way to do this is to use two one shots, one to trigger on the positive edge and the other to trigger on the negative and then OR those outputs together. What makes this project hard is the great difficulty maintaining symmetry with a square wave and a variable frequency. My way does not maintain symmetry but it does double your frequency. Any other way may involve a phase lock loop and that is tricky.

 

[duke37]

The problem with a one shot is that it will need to produce a short pulse at high frequencies and this will produce a very unsymmetric signal at low frequencies.

A CMOS 4046 phase lock loop with a divide by two flip flop could do the job, the 'CMOS COOKBOOK' by Don Lancaster says that a frequency ratio of 1000:1 is possible.

 

[lumley32]

i dont think the unevenness will be a problem, it was for a speedo on a bike to start with and the pickup it read off is very uneven and out of true, the outer thing is its only for a temp display so its well damped and not that important anyway!

when you say "one shot" clearly this is a form of logic, but i haven't ever hurd of it!

 

[lumley32]

ok after some "googleing" i found that a monostable 555 could be used as a one shot, but this gives me fixed timing and cant be less than the input pulse, am i missing something?

 

[(*steve*)]

Yes. If the signal has a fast fall time, then placing a capacitor between the signal and the trigger pin will convert the transitions into pulses. The negative going edge will become a pulse, triggering the monostable. In this case it doesn't matter that the input signal remains high or low any particular amount of time.