AVR-Chat

William,

Perhaps you may want to run your phototransistor output through a schmitt
trigger such as an 74ls14 chip which will make the pulses cleanly toggle
between digital one and zero. Otherwise there could be a slow rise and fall
shape to the output which could confuse your counting.

Seems like you could then use an external interrupt input to interrupt when
the input pulses, add one each time. Then setup a  timer to provide your one
second window. The display could run in the foreground to post answers from
the timer.

Al Welch

-----Original Message-----
From: William Nachefski [mailto:slaphappysamy@yahoo.com]
Sent: Tuesday, December 30, 2003 12:18 PM
To: AVR-Chat@yahoogroups.com
Subject: [AVR-Chat] AVR Tachometer


Hello All!
I am just getting started into AVR's.  I am seeking help on a
circuit.  I need to build a tachometer with opitcal pick up.  The max
RPM to be counted will be around 200,000 RPM.  I was told that pretty
much all of the tasks could be handled in code with a
microcontroller.  My pickup is a Phototransistor/LED its set up to
give one pulse per revolution.  So basically all I need is a
frequency counter with a 1 sec gate time, and then multiply the value
by 60,(my guess)Then to display the data on a 6 digit LED display.
I don't know really anything about M.C's but bought a few 28 pin
Mega8 chips to experiment with.  What should the circuit look like?
I am thinking the only thing I need on the board would be the display
+ multiplexing components and the Mega8 with a connector runing from
a input pin(interupt pin?)Let me know if I am on the right track.  Or
if someone else has built one of these.  Any help would be greatly
appreciated!

Thanks
Happy Holidays
William Nachefski




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