Maker Pro
Maker Pro

Op Amp with a/c output

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
From what I've read, it is a Hall sensor
The Trans harness pic shows the Input Shaft Speed Sensor as a variable reluctance type with a coil resistance of around 1kΩ. So that's what you've got if that pic indeed relates to your car model.
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
If the sensor is a 'coil' pickup of a rotating magnetic slotted disk then you'll have an AC signal output. If the sensor is a hall effect device then it MUST have a supply voltage to one side of it ergo one of the wires will have a fixed DC voltage on it.

The 13V (battery) you measured fits with my previous assumption - the other wire will have the return (speed) signal that is only present when the gearbox input shaft is rotating. That signal being a squarewave with a frequency proportional to the rotation speed of the shaft.

The comparator circuit I showed above would therefore accept the 'signal' (the NON 13V wire) on pin 6 and R2/R3 could be replaced with a preset potentiometer (wiper to pin 7).

You then take the output signal from the comparator at pin 1 and feed it back into the ECU, adjusting the preset so the circuit switches at the level of the input signal.


Excellent. Thank you for your patience and explanation. I had some general ideas, but nothing specific. So in a nutshell, if I understand correctly, the 13 volt DC signal will be the Vin and the comparator can be adjusted for the desired output with potentiometer? If I can simply adjust for 7,8, 10 VAC output, I have achieved what I need. Thanks.
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
The Trans harness pic shows the Input Shaft Speed Sensor as a variable reluctance type with a coil resistance of around 1kΩ. So that's what you've got if that pic indeed relates to your car model.

Since it only has two wires, could it be that both wires are AC self generating output, with no need for a voltage supply signal from the car's battery? For comparison, I read that 3 wire Hall sensor needs a reference voltage signal.
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
Excellent. Thank you for your patience and explanation. I had some general ideas, but nothing specific. So in a nutshell, if I understand correctly, the 13 volt DC signal will be the Vin and the comparator can be adjusted for the desired output with potentiometer? If I can simply adjust for 7,8, 10 VAC output, I have achieved what I need. Thanks.
Both of those understadings are wrong.

If it is a hall effect sensor, one wire must be to the 12V power, and the other is the signal out.

If it is a coil, it is truly putting out AC , and , to duplicate the original signal exactly, you would need an isolated, bipolar supply. But, based on the results others have seen, this should not be necessary.

To know exactly what would and would not work, we need to know what each wire is connected to in the ECU. For example, one of the two connections at the ECU is ground or 12V, we would need to design the circuit with that constraint.

Bob
 
Last edited:

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
Both of those understadings are wrong.

If it is a hall effect sensor, one wire must be to the 12V power, and the other is the signal out.

If it is a coil, it is truly putting out AC , and , to duplicate the original signal exactly, you would need an isolated, bipolar supply. But, based on the results others have seen, this should not be necessary.

To know exactly what would and would not work, we need to know what each wire is connected to in the ECU. For example, one of the two connections at the ECU is ground or 12V, we would need to design the circuit with that constraint.

Bob

Thanks Bob ! Could it be possible to be a two wire Hall sensor; one with supply voltage and one with output?
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
Yes, assuming the the sensor has metallic contact with the chassis, the ground could come from there.

But I still suspect that the it is really a coil.

Bob
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
Update: I hooked the multi-meter to the two wires inside the car and drove it. Look at my picture below and see the results. The one that is most puzzling to me is the meter positive lead hooked to red/white wire and the negative lead hooked to ground. At idle, and parked I get DC battery voltage (12-13 volts DC). However, while driving I can switch the meter to AC and now the signal varies 1.0 to about 4.0 VAC. Switching bac to DC again yields 12-13 VDC. How can I simultaneously get AC and DC? Any way I can boost this 4.0 VAC to 7, 8 or 10 VAC with a small amp or comparator circuit and solve this problem ? Thanks, sorry for dragging this out.
 

Attachments

  • ISS signal results.JPG
    ISS signal results.JPG
    65.8 KB · Views: 88

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,700
Joined
Nov 17, 2011
Messages
13,700
How can I simultaneously get AC and DC?
You can have a voltage that is the sum of a DC component and an AC component (see e.g. here).

With an ordinary multimeter:
When the meter is in DC setting, it will average the AC component if the frequency is more than a very few Hz. The average of an AC component is 0 V, so the meter displays the DC component only.
When the meter is in AC setting, typically a capacitor blocks any DC component. The remaining AC component is rectified, measured and displayed.


Og course, there exist advanced meters that perform so called RMS metering. These meters will calculate the RMS of the combined voltage and will in the case of a mixed waveform thus display a different value than an ordinary multimeter.


Any way I can boost this 4.0 VAC
You can use a series capacitor to block the DC component, then use an ordinary amplifier to boost the remaining AC to the desired level.
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
Can you explain a few things in your pic:
1) What is 'PCM' in this context?
2) Is Red/Blk the same as Red/Wht?
3) If Blue to Ground is 0V, why is Red to Blue different from Red to Ground?
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
What is the box with the S and V in it?

Bob
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
As has been pointed out, the signal driving the ECU/PCM needs to track the frequency of the signal from the sensor. That means the sensor signal needs to be reliable; but if the sensor triggers the error code then presumably the sensor or the connectors/harness has a fault?
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
Thanks again, very helpful. If it's no trouble, can you maybe post a schematic or drawing of the circuit, including how to input the DC battery voltage and the output "amplified" AC? Remember, I only need 8-10 VAC to send to the computer to "fool" it into thinking the sensor is good, thus turning off the check engine light, and passing the visual test at the smog station. Thanks, we are getting there !!t
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
Bearing in mind the previous discussions, can one of you draw up a quick schematic of how exactly I need to build it on a circuit board, how to feed the voltage in and out. I know this is asking a lot, but I really want to get it right, so I don't blow the fuse, PCM or other circuit. Really, thanks for everything. This has been a big help.
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
thus turning off the check engine light, and passing the visual test at the smog station.
Do they only do a visual test in the US? In Europe the test involves exhaust gas analysis at different rpms, so the error light would promptly come on again and the test would fail. A certain European car manufacturer fell foul of trying to cheat the emissions test.
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
Do they only do a visual test in the US? In Europe the test involves exhaust gas analysis at different rpms, so the error light would promptly come on again and the test would fail. A certain European car manufacturer fell foul of trying to cheat the emissions test.


Yes, and tougher requirements here in California. The first thing the smog inspector does is to verify the "Check Engine" light is off. If it is on, the test is over, automatic failure. Then they check for tampering or missing equipment. If the visible test passes, then they move onto the emissions tailpipe test and idle and 2500 RPM. The visual is my problem. I need the op amp, comparator circuit, transformer or whatever, to feed back into the speed sensor line to "fool" the computer into thinking there is no fault, and thus turning off the "Check Engine" light. I really only need help now with the schematic of how to build the circuit with what has been recommended in this thread. Once the circuit is in place, I can clear the code, go to the smog station, and be done with this. Thanks for any help !!
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
Joined
May 8, 2012
Messages
4,960
Can you explain a few things in your pic:
1) What is 'PCM' in this context?
2) Is Red/Blk the same as Red/Wht?
3) If Blue to Ground is 0V, why is Red to Blue different from Red to Ground?
What is the box with the S and V in it?

Bob
These questions have not been answered. Until they are this thread is going to be tantamount to a fishing expedition.

Chris
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
Sorry to bang on, but I'm still having a problem understanding the logic behind this. Correct me if/where I'm wrong :
1) If the ISS sensor output is only 1.5VAC at idle, it (or its connection) is faulty.
2) If you build a circuit which has output pulses whose negative-going excursions go at least abou 7V below the battery +ve voltage you can clear the error light.
3) The visual test will pass.
3) The inspector will then proceed to do the emissions test.
4) The test is done at more than one input shaft speed.
5) Your faulty ISS will be in use for the emissions test.
6a) The built circuit is also in use during that test. If the test is passed you have cheated the test.
OR
6b) The built circuit is not used for the emissions test. The error light will come back on. The test is failed.
6c) Cheating the test is illegal where you are.

Note: Encouraging unlawful activity is forbidden by the Terms of Service of this site.
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
It is not illegal if the code is cleared, as the onboard diagnostics allow the owner to do this, and I already have cleared it several times. The car otherwise passed the tailpipe emissions test, which the system has not been tampered with. Emissions system tampering is illegal, no electronic controls under California and Federal laws. The transmission is not part of the emissions test, but they lump any light into the test. The local smog referee has the authority to waive any requirement, but cannot see me for a few months.
 

HomerDodd

Sep 6, 2017
53
Joined
Sep 6, 2017
Messages
53
You can have a voltage that is the sum of a DC component and an AC component (see e.g. here).

With an ordinary multimeter:
When the meter is in DC setting, it will average the AC component if the frequency is more than a very few Hz. The average of an AC component is 0 V, so the meter displays the DC component only.
When the meter is in AC setting, typically a capacitor blocks any DC component. The remaining AC component is rectified, measured and displayed.


Og course, there exist advanced meters that perform so called RMS metering. These meters will calculate the RMS of the combined voltage and will in the case of a mixed waveform thus display a different value than an ordinary multimeter.



You can use a series capacitor to block the DC component, then use an ordinary amplifier to boost the remaining AC to the desired level.


Harold: can you give me a schematic of how to build/install this circuit? Thanks.
 
Top