Thanks,
I will have this mod done and tested by tomorrow (sat).

 

Remove Z2.
Replace R2 with a 10k Ohm resistor.

The LM358 is a dual opamp. You need to connect the output of the side you're using to the non-inverting (+) side of the unused side, and the output of the unused side to the inverting (-) input of the unused side. Otherwise, it may oscillate and cause problems.

Wookie, without the zener won't the input transistors on the op-amp cook when there is a spike on the line?

 

Hi all,
I made all the suggested modifications, with one execption, I could not get a 10K resistor so used two in series to give 9.94K.

Also tested this new config with the 6.8V zener both in and out of circuit. I am still getting the same results as before, ie ECU is good, but no speed indication.

Jacked the car up and measured the pulsed output from the VSS as 4.73v and now with the mods made above the speedo is being fed 6.6v through the op amp and it pulses in sync with the vss output. Yet it will not move the speedo. .

I am really at a loss to know what to do now, your help is much appreciated.

 

If you are getting 6.8v out of the opamp, you probably do not have the inverting input connected to the output.

 

Sorry for my confusion, but what voltage am i supposed to see being fed to the speedometer?

To clarify further, I was given another Op Amp P/N NTE928S by the Store, they said it was the same as the LM358 and I should use the connections as per the wiring diagram that (tom66 made) as follows:


Connections have been made are as follows:
Pin 1: 8 volts from voltage regulator
Pin 2: Output A to speedometer
Pin 3: Jumped to pin 2
Pin 4: Input from VSS signal
Pin 5: Chassis ground


Here is the linj to the NTE spec sheet.
http://www.nteinc.com/specs/900to999/pdf/nte928s.pdf


I have done this now is it correct?

 

Sorry for my confusion, but what voltage am i supposed to see being fed to the speedometer?

To clarify further, I was given another Op Amp P/N NTE928S by the Store, they said it was the same as the LM358 and I should use the connections as per the wiring diagram that (tom66 made) as follows:


Connections have been made are as follows:
Pin 1: 8 volts from voltage regulator
Pin 2: Output A to speedometer
Pin 3: Jumped to pin 2
Pin 4: Input from VSS signal
Pin 5: Chassis ground


Here is the linj to the NTE spec sheet.
http://www.nteinc.com/specs/900to999/pdf/nte928s.pdf


I have done this now is it correct?

The op-amp is in an unusual package (looks like SIL - single in line) instead of a DIP (dual in line), as I would recommend. The LM358 is so common, it is about 35 cents in low quantity; you should make certain they don't have any.

Vss is ground (technically speaking it is Vee as the op-amp is bipolar.) Connect Vss to then negative terminal of your battery, or in most cars to the chassis.

For your op-amp, you should also connect pins #6 and #7 to the Vss terminal to prevent oscillations as you are only using a single channel of the op-amp.

 

Ok I have started again.
I managed to get an LM358(M) and built a new board as per the wiring diagram.
Op amp is now connected as follows:
P1: To Speedometer input
P2: Jumped to P1
P3: 10K resistor and vss output signal from the sensor
P4: To chassis Gnd
P5: Jumped to P1
P6: Jumped to P7
P7: Jumped to P6
P8: To voltage reg.

Result on driving: VSS code does not trip (which is OK), however still no speedo reading.

In your last post you mentioned to connect 6 and 7 to the vss terminal, was this for the NTE amp or the LM358? Also should I remove the 10k resistor and go back to a 47 ohm ?

This must be as frustrating for you as it is for me. LOL

 

Ok I have started again.
I managed to get an LM358(M) and built a new board as per the wiring diagram.
Op amp is now connected as follows:
P1: To Speedometer input
P2: Jumped to P1
P3: 10K resistor and vss output signal from the sensor
P4: To chassis Gnd
P5: Jumped to P1
P6: Jumped to P7
P7: Jumped to P6
P8: To voltage reg.

Result on driving: VSS code does not trip (which is OK), however still no speedo reading.

In your last post you mentioned to connect 6 and 7 to the vss terminal, was this for the NTE amp or the LM358? Also should I remove the 10k resistor and go back to a 47 ohm ?

This must be as frustrating for you as it is for me. LOL

Sorry, the jumpers I specified were for the NTE chip, the LM358 would have:

#1 - output
#2 - jumper to 1
#3 - point between R2 and Z2
#4 - ground (chassis/battery)
#5 - jumper to 4
#6 - jumper to 4
#7 - no connection (or jumper to 4, see which works best)
#8 - power supply

Pin #1 is marked with a circle next to it, or on some chips is the bottom left pin from a small mark on the left; pins are counted CCW.

One of the first things I would check would be the voltage regulator. Are you getting a stable 8V output? Have you got the regulator the right way around? Is it connected properly to the battery? etc.

I don't think the 10k resistor will cause any harm at the moment, leave it in.

 

Tom66

This is the datasheet link for the LM358M amp i have, the pin config is on page 9. Looking at the schematic there seems to be an internal interconnect between the amps, will running the pins on the unused section to ground cause a problem?

http://www.datasheetcatalog.org/datasheet2/d/0krxqjyrr14uhy7yk1if661zzqwy.pdf

I have checked the voltage reg output, it is giving 8.07V at pin 8 with 12v applied.

Thanks for the support!

 

Tom66

This is the datasheet link for the LM358M amp i have, the pin config is on page 9. Looking at the schematic there seems to be an internal interconnect between the amps, will running the pins on the unused section to ground cause a problem?

http://www.datasheetcatalog.org/datasheet2/d/0krxqjyrr14uhy7yk1if661zzqwy.pdf

I have checked the voltage reg output, it is giving 8.07V at pin 8 with 12v applied.

Thanks for the support!

The interconnect is for the power connections between the two amps; it is only indicating that the power pins are shared for the two op-amps on the chip.

The 8.07V output is fine for the voltage regulator, they are usually specified with a tolerance of ±4% or so, in this case it could vary from 8.32V to 7.68V but it should remain stable at one output.

 

tom66
I rewired the board as per your suggestion (omitted pin 7 for the moment), tested on car with the same results ECU ok, no speed reading.

FYI.
I tested on the bench using 11.3v input, and measured voltages on the input and output lines on the board, saw 0.527V on input line and 6.09 on the output to the speedo.

Jumped pin 7 to ground pin 4 and saw the same results.

Is this result what is expected?

 

tom66
I rewired the board as per your suggestion (omitted pin 7 for the moment), tested on car with the same results ECU ok, no speed reading.

FYI.
I tested on the bench using 11.3v input, and measured voltages on the input and output lines on the board, saw 0.527V on input line and 6.09 on the output to the speedo.

Jumped pin 7 to ground pin 4 and saw the same results.

Is this result what is expected?

Can you show us a picture of your board? I want to make sure everything is connected okay.

 

Photo attached.

Is this Ok

 

I can't see the wiring, I'd probably need to see the bottom as well.

 

This will probably be your worst nightmare! As you can see Im not good at this at all.

 

Don't worry, I've done much worse.

Blue and red wires appear to be touching, might want to check that out. If you probe the junction between the resistor and zener, do you more-or-less get the same voltage as the input?

 

blue and red are in fact touching. the red wire is the ground for the voltage reg.

Voltages between the zener Z2 and resistor R2 and the input are almost identical 0.573V

 

Let's try something else. Connect pin #2 to ground and disconnect it from everything else, leave pin #3 connected to the signal. Measure the output, then connect pin #2 to the voltage regulator, it should change if the op-amp is working correctly.

 

Performed a Bench test with 10.46 voltage source.

Pin 2 connected to gnd (and nothing else) out[ut to speedometer is 6.71V and input signal wire reads 0.575V

Pin 2 connected to output of voltage reg output to speedo is 0.007V and input signal wire reads 0.728V

 

Performed a Bench test with 10.46 voltage source.

Pin 2 connected to gnd (and nothing else) out[ut to speedometer is 6.71V and input signal wire reads 0.575V

Pin 2 connected to output of voltage reg output to speedo is 0.007V and input signal wire reads 0.728V

It is apparent then the op-amp is working correctly, but I can't figure out what is wrong with your circuit. I would double check all your solder joints - some of them are quite dodgy.