This shows the prototype. The processor is an ATTiny45. The current code size is 1190 bytes, so it will fit comfortably on an ATTiny25 as well. The LED display is an HC4LED that I purchased from SparkFun. You can also purchase the HC4LED from The HC4LED has a SPI like interface.

The pulse generator is generating a 10 Hz signal (My multi-meter measured it as 9.9 Hz). A 10 Hz signal would correspond to 600 RPM. You can see that the Tach is displaying 593 RPM (which agrees with the 9.9 Hz signal).

So far, I've tested the circuit with 1 Hz through 1,000 Hz signals, which corresponds to 60 RPM through 60,000 RPM. The processor is currently only running at 1 MHz, and is capable of running at 8 MHz using the internal oscillator. So it could deal with 480,000 RPM as long as there is only 1 pulse/rev. Bigger...

Index Next

Home - Electronics - Index

Copyright 2007 by Dave Hylands