LM2917 tachometer cirquit problem!

[panosrc]

Hi to all. I am new here and I would like to ask you about a problem I have.
I am trying to measure my car's rpm via the ignition module signal that goes to the coil.
I have made the cirquit thats in the picture that I have taken from a member of this forum that put that to a VW beatle and worked fine. So I use lm2917 14pin and the only thing that I can read to my voltmeter is some milivolts until 1500 rpm and after it outputs nothing! Can someone help me? Thanks in Advance. Here is the cirquit:
**broken link removed**
And these are the capacitors I have (in case someone see that these are wrong.
**broken link removed**

 

[Les Jones]

I suspect you have the polarity of the diode reversed. Can you post a photo of the underside of the board so we can check if the board is wired as in the schematic. Also you have a preset on the board which is not shown in the schematic so can you show how this is connected.

Les.

 

[panosrc]

**broken link removed**
Here is tha pic of the cirquit. I hope that helps!

 

[ronsimpson]

I suspect you have the polarity of the diode reversed.

Interesting thought.
Pins 1 and 11 work in the range of 0 volts to (supply-1.5). so 0 to 10.5V
If the diode is right then there should be about 0.6 volts on pin 11. If the diode is wrong then there will be almost 12 volts on pin 11.
Simple test.

 

[alec_t]

I agree; the diode is reversed.
Pins 6 and 7 should be NC, but you seem to have a wire going there?

 

[panosrc]

Soryy I have to mention that the input resistor is in the photo 4.7kohm just to try.

 

[panosrc]

No pins 6-7 no connected. The diode has to be a specific one? I have put 1n4004. And the silver line goes to ground is that reverced? Thanks all of you for your help!

 

[ronsimpson]

1n4004

That diode is fine.

 

[MikeMl]

If you connect this to a the points in a real distributor, you will likely blow up the LM2917. It needs a much more sophisticated input pulse conditioning network.

 

[alec_t]

Mike makes a good point. The voltage across the contact-breaker is a nasty spikey thing, by virtue of the inductance of the primary coil.

 

[panosrc]

Sorry not to the distributor...I ment to yhe coils - that sents the pulse to the dist. So now that I connect the input to the negative pole of the coil is wrong? Where do I have to connect that?

 

[Les Jones]

After seeing the underside of the board I think the diode is connected the correct way round. (I originally assumed that it was built on stripboard with the tracks at right angles to the axis of the IC. It looked like the negative of the diode was connected to pin 12 (ground.)) I have not yet checked the rest of the tracks.
I agree with Mike that the input circuit needs to be modified by adding a zener diode to ground or a normal diode to + 12 volts as the signal from the contact breaker will pulse up to about 300 volts when the points open. There is a good chance that these spikes have allready destroyed the IC. I think I would also add a decoupling capacitor between pin 9 and ground.

Les.

 

[MikeMl]

Sorry not to the distributor...I ment to yhe coils - that sents the pulse to the dist. So now that I connect the input to the negative pole of the coil is wrong? Where do I have to connect that?

The points in a Kettering ignition are connected to the primary of the ignition coil....

See post #4 in this forum thread.

 

[Les Jones]

The connections look correct as far as I can tell except I can't find the 200 K resistor that should connnect between pin 3 and ground and I cannot work out how the preset is connected.

Les.

 

[panosrc]

I really thank all of you because my electronics are on a beginner level. So what would you suggest to do? I also know the wire that the ecu outputs for the tachometer. Will it help?

 

[panosrc]

The connections look correct as far as I can tell except I can't find the 200 K resistor that should connnect between pin 3 and ground and I cannot work out how the preset is connected.

Les.

Instead of the 200k I put the pot at 200k.

 

[alec_t]

After seeing the underside of the board I think the diode is connected the correct way round. (I originally assumed that it was built on stripboard with the tracks at right angles to the axis of the IC. It looked like the negative of the diode was connected to pin 12 (ground.))

I made the same assumption as Les, so if he says the diode orientation is ok then I'll go along with that. I didn't have the energy to fathom out the underside .

 

[panosrc]

Xaxaxa...I made the cirquit 3 times at different boards...

So what can I do to take the coils signal to measure the rpm?

 

[Les Jones]

To protect the input from the high voltage spikes from the ignition coil primary I suggest connecting a zener diode ( Any one between 3.3 and 6.8 volts should do.) between pin 1 of the IC (Positive) and ground (Negative.) I would first test the circuit using a signal generator or if you don't have one then an AC supply of between about 5 and 20 volts. This will also enable you to calibrate it. If your mans frequency is 50 HZ then it should read 1500 RPM. If your mains frequency is 60 HZ then it should read 1800 RPM. (Assuming it is to be used with a 4 cylinder 4 stroke engine.)

Les.

 

[MikeMl]

...So what can I do to take the coils signal to measure the rpm?

Look at the coil (primary) signal with an oscilloscope. After you see what is there, design a circuit to work with that signal. You are grabbing a design off the internet with no understanding of what you are connecting it to.