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Saturday, 22 September 2007 00:05 |
"So, can you make a tachometer for my lathe?" I got asked and replied "Yes.".
This dialog started a new project. Im going to use a infrared based sensor and a 7-segment based visual output.
The speedrange is 50 to 2750 turns per minute. A advantageous place for sensor installation has a diameter of 50mm.
The 32 available pins of an Atmega16 aint enough for four 7-segment LEDs, ok it would be, but I would use up too much pins. Every two LED-modules will be merged.
Time for a first test of the output:
Now the output is limited to identical digits.
The same from behind:
After this I implemented a interrupt routine which switches between the digits, aka multiplexing:
Now it is possible to choose individual digits.
This setup uses 7+2=9 pins, 7 pins for the segments and 2pins for two digits. Another nine pins will be needed for all four digits in the final circuit, otherwise it would get too dark.
The sensor
I build a sensor of one infrared led and one infrared diode. It didn't work well. It had bad problems with electromagnetic interferences. Slow motor speeds worked well, but at a specific point it made peaks into the signal and this caused the display to flutter.
The DIY sensor:
A few weeks later I had the chance to scavenge a copy machine. There I found a just fitting sensor.
The sensor module:
It runs best in 3cm distance and in the range of 2cm to 4cm. White or reflecting surfaces will cause the output high (5V).
BTW there is more interesting stuff in a copy machine.
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Last Updated on Wednesday, 13 August 2008 09:52 |
