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how to make tachometer with 7 segment display for single cylinder 2 stroke 6v ignition..can anyone help me? Answered

i found a diy project from https://www.instructables.com/image/FU19QM5GH4NN2QX/Building-the-circuit.jpg
but i want to use only 3 led(7-segment display) instead  of  4 led..
and another problem is this circuit only fit input signal from 12v ignition 4 cylinder ( car ),
but mine is 6v single cylinder 2-stroke( motorcycle )..
what i have to modify so than i can make a circuit that can use 6v signal to the ic and only use 3 led(7-segment display..
can any give an opinion or some one that have done this to help..im not to good with electronic but i understand english. :-)

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user
steveastroukBest Answer (author)2011-12-25

Changing the display is easy. Just put the three most significant digits on the circuit.

Changing the scale is also pretty easy. Play with the value of the "100+47K resistor" - make it smaller.

Steve

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user

thanks steveastrouk..
but what do you mean by change the significant digit? the circuit in the link above use 4 piece of 7 segment led..but i want to use only 3 pieces of 7 segment led..this circuit use alrdeay pogramed ic but not pogramable ic..how i supposed to do that?

and where i suppose to add the resistor?is it ok if i want to use for 2 stroke single cylinder?i mean that is this circuit is suitable for 2 stroke cycle because this circuit are made for the car (4 stroke system?? with 4 cylinder)
i hope you can help me with a step to tho that..

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user

The design has a thousand, a hundred, a ten and a unit display.
Omit the unit display, then you have THREE of them.

I said exactly where to CHANGE the resistor - where the 100+47K resistor is. Yes, the circuit will work for a 2 stroke, single cylinder.

Steve

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user

ok..i think i can catch it..thanks steve..!!
can i refer again to you if i had a problem with the circuit?

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user

1 more steve..
the 100 + 47k that you mention is for the signal from the ic (lm2917-frequency to voltage) to the led part right? that is for changing the scale from 4 cycle to 2 cycle right?
bwhat i want to have is the signal from the igniton coil to ic (lm2917-frequency to voltage) ..the design if for 12v so how i supposed to do to change it for 6v ignition?

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user

Yes.

Looking at the interface circuit, it should work OK for 6V ignition.
If it doesn't, change the Zener to a 6V one.

Steve

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user

great,thanks again steve.. :-)

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user

steve i wanna ask somthing else,if i want to use 8x2 lcd display (http://www.cytron.com.my/viewProduct.php?pcode=DS-LCD-082A&name=LCD%20%288x2%29)
instead of 7segment display,can i do that?

if yes,should i built another programable circuit to compute the voltage into character on the lcd display?or i just plugin the output from the frequency to voltage to the lcd input?

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user

You need computing power to drive the 8X2.

You COULD display the speed on a DVM module.

Steve

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