# tachometer in child's make-believe toy



## Billy_Bob (Sep 11, 2008)

A programmed microcontroller would do the trick. You could also use one of these to make an engine sound and make it get louder as the speed increased.

Ask the microcontroller experts here...
http://forums.parallax.com/forum.php


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## freedomlives (Aug 6, 2012)

Use a 555 timer and a potentiometer connected to the throttle.
http://www.daycounter.com/Calculators/NE555-Calculator.phtml

However, it is clear from the calculator that the frequency output requires both resistors to change in order for the pulse width to stay the same. This may or may not matter though.


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## av-geek (Jan 15, 2012)

Yep a 555 timer is exactly what I ended up using  I also used Billy Bob's idea and attached the output to a transistor and a small speaker, so it makes a buzzing noise like an engine running...works perfect! I tweaked it so at full throttle, the tachometer needle goes right up to about 4000 RPM, just up to the redline I also connected up some of the other gauges so they go up and down too. This was a fun project, and the boys love playing with it!


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