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Tachometer with LCD readout

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actionplus

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Has anyone tried out this project? If so can you direct me how to start with it.

I am thinking of using a Allegro Hall effect digital sensor along with a 16F84 or a 16F877. The LCD would be a Hitachi.

Hopefully someone will be able to help me out on this. :lol:
 

crust

Member
Yes, I have done such a device. It did not display the speed on an LCD, but the lcd interfacing is very easy to do. The hard part is converting the timing of the pulses from the hall effect sensor into RPMs. The frequency is given by 1/t where t is the period of the pulses. Doing a "1-over" in micros is not always straightforward. Alternatively, you can count pulses in a given amount of time, but you need to have enough pulses in your sample period to give an accruate estimate of the speed (alternatively, you can digitally filter over the last n sample periods).
 

crust

Member
Re: Readout

actionplus said:
How were you able to know what the rpm was without the LCD?
I used the serial port of the micro controller to output the speed to a computer. In addition, I had a set of 7 segment displays that I scanned to show the current speed. I *might* have the code on a floppy as this was 8 years ago -- However, to do the timing->frequency conversion, I used a 6811 which had a special FDIV instruction to perform a large part of the math. If you used an AVR for instance, you could get a c library for it and the divide is done for you.
 
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