Hi to all,

Just trying to get a project going for my sons lathe, it sounded simple when he asked me to make him a speed readout for it!

Since I already had what I believe is an ideal IC for the job, the ICM 7225 counter/display driver and some spare 7 segments and an Slotted Opto sensor which I intended to get my pulse from (the pulse would hopefully occur from a driven disk with a hole to allow the LED to Excite the Phototransistor), well that was the plan

Anyway the problem is that I can't understand how to interface the pulse and the ICM7225 IC, even though it says in the Datasheet that one of its uses is a Tachometer, it fails to give even the most basic of examples that I could build on, and I'm no Einstein so stuck!

The LED side of the circuit isn't a problem to me, just the interface from pulses to RPM circuit.

If anyone knows how to do this I would be very grateful and would be able to get my project off the ground, and onto the bench! hehehe

I have included my (pretty poor) but functional drawing of the optocoupler circuit which seems to work ok, though I don't have any experience of the speed these are capable of working at or if I should have one single hole or multiples?

Also I have posted the 7225 datasheet, I just hope someone will take pity on me and can help.

Thanks for taking the time to read this post...............Al

According to the data book, the count input has a schmitt trigger so a noisy input will be okey. My data book also says it triggers on the negative going portion of the input trigger. I think it will work if reposition the 1K resistor on the output of the optocoupler from the collector to Vcc, ground the emitter and tie the junction of that collector and the 1K to the count input.