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Discussion Starter · #1 ·
Ok, maybe this belongs here, maybe in mods, I dunno.

So.

If one wanted to create sequential shift lights for a tach, how would one go about doing that?

The tach functions by an electrical charge, the faster the engine goes, the higher the current, right? So all I'd have to do is figure out at which (amperage, voltage...?) I want the LEDs to light up, and then what, add what electrical components (resistors, capacitors...?) in series to trigger the LEDS?

Obviously, I have no clue how to do this, but I think it would be a fun project. Any ideas?
 

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Buy a SPA tach. That's how I did it.
 

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Discussion Starter · #3 ·

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I am not sure how a tach works, is it increase in current or voltage, or just a microprocessor reading the revolutions of the wheel (like a bicycle trip computer)?

If it is an increase in voltage, then you could use a variac, and when the voltage is below a threshold, it acts like an open circuit, and when the voltage passes the threshold, it acts like a short circuit.

Find more info on how the tach actually works, then design the leds.


mitt
 

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mitt said:
I am not sure how a tach works, is it increase in current or voltage, or just a microprocessor reading the revolutions of the wheel (like a bicycle trip computer)?

If it is an increase in voltage, then you could use a variac, and when the voltage is below a threshold, it acts like an open circuit, and when the voltage passes the threshold, it acts like a short circuit.

Find more info on how the tach actually works, then design the leds.


mitt
I think you're talking about a varistor. Variacs are variable transformers. On the plus side, varistors cost way less $$
 

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Discussion Starter · #6 ·
Ok, I did some more research. The tach pickup is inside the crankcase, and for every revolution of the crankshaft, it sends out a signal, and the tach just counts the signals.

So basically I need to convert the digital signal to an analog one to use with this "Bar Graph Display Driver" LM3914N circuit. Here goes nothing!
 

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Discussion Starter · #8 ·
holycrap... thats exactly what I'm looking for! I even ordered the 2917 circuit today too... awesome
 

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whited3 said:
I think you're talking about a varistor. Variacs are variable transformers. On the plus side, varistors cost way less $$

I actually meant to type Bilateral Trigger Diac, but my brain wrote variac.

mitt
 
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