Frequency to Microprocessor input.

[Huttojb1]

To implement a tach, you have two choices: count events per unit time, or measure the period between events using a high frequency clock (like the cpu clock of a microprocessor). Doing the former with any significant resolution means waiting a relatively long time between updates (like a second per update). Doing the latter means you can get higher resolution in a shorter time (like the interval between successive power strokes). Doing the latter, however, requires that you do a division to get the RPM:

f=k/period, where k is a constant.

Thanks Mike. I'm sure I will go through the pain once I start trying to write the capture.

Jason

 

[spec]

Hey Spec,

Sorry the diagram wasn't viewable on my phone last night so didn't see you had posted it.

Thanks ever so much, I will need to source the 6N139, but will definitely try the design for my solution.

Will definitely get back to you with the results.

Thanks again, Jason.

No probs HJB- I only posted the schematic about 3.5 hours ago.

It turned out that, according to my analysis, nothing much changed from the rough sketch, which is good news.

Yes, you need a 6N139.

spec

 

[Huttojb1]

Spec, all components ordered and should be here Monday.

 

[spec]

Spec, all components ordered and should be here Monday.

Good man

spec

 

[Huttojb1]

While I was waiting for my components to come I decided to give Les's idea a crack, mainly to increase my knowledge and also alittle bit of curiosity

So I put a 10nf cap to ground, 10k in series, a 5.1v zener to ground and measured the output. Although the signal was a hell of a lot cleaner it still showed a massive variation in frequency. I would expect this was due to noise spikes still on the output.

How would I get rid of these noise spikes.

See files.

Jason.

 

[Huttojb1]

Hello.

I have finally got the components and tested the 6n139 option without success. I'm only doing this on breadboard to try and see how I got on butnot getting anything readable on the scope.

Spec, can you please advise.

Jason

 

[Huttojb1]

Going back to the zener option with alittle more filtering gives me a decent signal.

 

[Huttojb1]

After earthing pin 3 it all magically started to work.

See results.

Would like to thank the people who have helped me on this.

 

[spec]

After earthing pin 3 it all magically started to work.

See results.

Would like to thank the people who have helped me on this.

No probs HJB,

Glad it all turned out OK.

spec

 

[Huttojb1]

Spec.

Fitted and seems to be working good. Thank you for your help.