Hello, I am working in the speed control of DC Motors. I have used MOC 7811 for sensing the speed which gives one pulse per revolution. These pulses are counted using counter(continuous count).  I want to convert this in to RPM.How can I do this?

Frequency counter. So typical is place a counter, set it as up counter.

Place a timer, or clock, will use as gate,  1 Hz, and supply that to

counter enable. Set up interrupt on timer gate going negative. In ISR

read counter, reset it to 0.

The count that you read during ISR is pulses/sec, eg. RPM. Resolution

1 Hz or 1 RPM.

You can set the gate to 10 Hz, and multiply the count read in ISR by

10. This gives you faster  frequency measurement. But resolution now

10 Hz, or 10 RPM.

Regards, Dana.

Forgot, counter width must be > max RPM you are going to read,

So if max is 10,000 rpm, then counter is 16 bits.

Regards, Dana.

1s response seems quite large. Shorter gate period makes your system respond faster but lowers resolution.

If you want to get the fastest response time, use period measurement (use the pulses from your motor as gate signal, and count the number of clocks from an internal clock). That way you get new measurement for each motor revolution (but accuracy decreases with higher RPMs).

The use of period vs frequency counter approach has a number

of characterisitics that need to be examined. For example period

counters used as a F counter at higher frequencies generally burn

more power as an approach because of the resolution clock F

needed. Also be aware of enable timing limitations on a PSOC

counter.

Attached some considerations for both.

Regards, Dana.