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av-geek 07-21-2012 08:44 PM

tachometer in child's make-believe toy
I scavenged the old instrument panel out of a boat that was being junked. It has a tachometer, volt meter, temperature, oil pressure, and tachometer on it. It also has a light switch, a throttle control, and a keyswitch. I am looking to connect some of these things up to a 12 volt source for a 5 year old boy to play with in his tree house, so it will be like a ship or something, and actually be semi-realistic.

The keyswitch will be the "master" switch to the panel, and will make the volt meter jump up to the power supply voltage (I am using a landscaping light transformer with a bridge rectifier behind the panel) I am going to take the light switch and connect it up to the lights inside the gauges, and also to a few small lights around the bottom of the treehouse. I have plans for some of the other gauges and switches too, and hope that this will be really fun for him to play with. Since it's designed to be in a boat, it should withstand the weather being out in a treehouse. (besides, by the time it really starts to fall apart, he will probably be of age to where he wants a real boat!)

One of the challenges though is I want the tachometer to go up when the throttle control is pushed up, like it would if it were really connected to an engine. A typical tachometer measures pulses from the ignition system in an engein. What kind of electronic gadget, I am thinking maybe some type of oscillator with a varying frequency, that I can connect to the tach to make it go up when the throttle control is pushed forward.

Billy_Bob 07-22-2012 06:51 AM

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...

freedomlives 08-15-2012 03:04 AM

Use a 555 timer and a potentiometer connected to the throttle.

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.

av-geek 08-18-2012 09:09 PM

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 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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