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Topic: LM2917 Frequency to Voltage Converter (Read 7 times) previous topic - next topic

matinzk

Hi everyone.

I have made use of a frequency to voltage converter (LM2917, 8pin version) to convert the frequency from my car's RPM tach signal wire to voltage to then read it with my Arduino and make a digital RPM readout.

Here is the circuit I have done:


The resistor, capacitor and the diode connected to the tach signal wire is to get rid of the DC offset.

There are 2 problems at the moment:-
1) The chip doesn't convert the signal properly, the higher the RPM from the car the less accurate the output voltage, hence a very off RPM compared with the RPM dial in the car. For example when car's RPM dial reads 3000 RPM the digital output reads 2400 RPM.

2) The chip itself gets very hot even if there is no signal into it and even when nothing is connected to the output voltage pin.

Has anyone got any experience with this chip at all?

Any help is appreciated.

Thanks

winner10920

A quick look at the datasheet suggests the diode on the input isn't necessary, it seems desined to have the tach ac input, no experience with the ic tho

matinzk

I've checked the current that the circuit takes and it's about 65mA. It's supposed to take less than 5mA. This is with the input signal frequency and the output voltage disconnected.

Anyone?

wanderson

In your circuit have you connected pins 4 & 7 to pin 6?  That schematic indicates they shouldn't be, but with that style it would be easy to misread that.
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Far-seeker

#4
Aug 23, 2012, 10:56 pm Last Edit: Aug 23, 2012, 11:04 pm by Far-seeker Reason: 1

In your circuit have you connected pins 4 & 7 to pin 6?  That schematic indicates they shouldn't be, but with that style it would be easy to misread that.


I think in the style used by matinzk only dots or filled circles indicate connected lines.

Edit: Added missing word I thought was there.

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