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Old 28th April 2014, 17:14   #16
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Default Re: Custom Tachometer - Electronics related queries

tsk1979, the main reason I've used a hall sensor here is because the vehicle is an off road buggy built by us.
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It doesn't have an alternator or in fact any way of producing an analog signal. When there is an analog signal, I think a simple op-amp will do the job as a square wave generator. Counting the pulses of the spark plug is another way but measuring it is a far more complicated process than using hall sensors.
Also, with the hall effect sensors I can fine tune the accuracy by using more sensors/magnets and changing the calculations accordingly.

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Old 29th April 2014, 17:40   #17
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Default Re: Custom Tachometer - Electronics related queries

Hey Arjun18,

Congrats on the second overall award!

Quote:
Originally Posted by arjun18 View Post
Counting the pulses of the spark plug is another way but measuring it is a far more complicated process than using hall sensors.
I'm not agreeing or disagreeing with you here - but i want to know your reason for saying so.

If i'm not mistaken, you can take a strand of wire, wrap it several times around your spark plug lead - and everytime the high voltage goes through the lead to make a spark, the inductance will create voltage on the strand of wire you added.

You can then measure that voltage with the arduino (after adding some protection).

cya
R
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Old 1st May 2014, 12:11   #18
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Default Re: Custom Tachometer - Electronics related queries

Quote:
Originally Posted by Rehaan View Post
I'm not agreeing or disagreeing with you here - but i want to know your reason for saying so.
Hey Rehaan, the main reason we require a tachometer is to tune the CVT, for which we need to compare the RPM of the engine with that of the driven pulley.
Since the driving and driven pulley are in the same enclosure, it's easier to set up the system that way.

If I'm going to measure pulses from the spark plug, I'll have to ensure the signal is conditioned properly for the arduino, using a 7805 will introduce a slight lag which may or may not matter,
I'll need to use a 555 which requires very precise values of components to produce a +- 15 RPM accuracy, transistors, and of course it's own power supply. The car doesn't have an alternator and we need to preserve whatever battery power we can, every little bit helps.
I'll also have to estimate the number of turns to make around the plug depending on the gauge of the wire, etc.
Using a voltage divider will complicate the circuit(not that it's complex, but more so than the hall circuit).

Overall, it's only the practical aspect of using a spark plug coil vs hall sensor that favors the hall sensor more for our requirement, hope I've been of help! :P
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