Trying to replicate an accelerator pedal using a differential amplifier

In summary, U1A and U1B are subtracting 568 mV from U2A, which is causing the output to be different than what is being predicted by the schematic.
  • #1
jacadams
1
0
I'm trying to replicate the voltages coming from an accelerator pedal, to the ECM, on 6.0 L Diesel engine. I acquired the three separate voltages using an oscilloscope. I have access to two analog output channels on the dyno. Out of the three voltages two them follow each other by a difference of 0.6 volts. Going from 1.58 to 4.26 and 1.00 to 3.64, equating to 0 to 100% throttle. I have uploaded the current schematic I'm trying to utilize to achieve this goal. V1 will always be 12v and V2 will be an analog output, going from 1.58 to 4.26. My original schematic was only utilizing one op amp as a differential amplifier, but the V-(pin 2 of U2A) was rising with V+. I was not getting a constant 0.6v difference between the two signals. So I then added two voltage follower circuits, as shown, to buffer the signals going into U2A. If I run the current schematic in my simulation software, everything works out great. I get a liner voltage out at Probe1 rising from 1.00v to 3.64, which is what I'm looking for. When I build the schematic in real life and test it I am getting a more constant voltage difference, but I'm not able to dial it in precisely. After some trouble shooting I found that I'm not getting the same voltage in as I'm getting out on probe 3 and probe 4. Instead of going from .568 v to .568 v it goes .568 to .738v. I've tried surfing for half a day on a solution and I'm not getting anywhere. Any help would be appreciated. Thanks!
 

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  • #2
what type of op amps are you using? some have outputs that can't get lower than about .7 volts. Look for an op amp that is rail-to-rail, sometimes abbreviated R-R.

Alternatively, you could change the resistors to make the output of U1A and U1B double the value you have now, and then halve the difference by making R5 and R3 to 3k instead of 1.5k.

If your real life part is indeed a LM358 then, according to the datasheet, it should be able to go to as low as .005V and then i don't know what the problem is.

For best accuracy (on the scale of ~1mV, not enough to cause .17V of error), the input pins of the op amps should have the same thevenin equivalent resistance, in this case this would be accomplished by adding a 500Ohm resistor between pin 1 and 2 of U1A.

Don't forget to put decoupling caps on the supply pins of all of the ICs.
 
  • #3
U2A subtracts the 568 mV from U1A instead of adding it.
Could you go to a +/- 6 volt power supply instead of a +12 volt power supply?
 

1. How does a differential amplifier work?

A differential amplifier is a type of electronic amplifier that amplifies the difference between two input signals while rejecting any signals that are common to both inputs. This means that it amplifies only the desired signal and reduces any unwanted noise or interference.

2. What is the purpose of using a differential amplifier in replicating an accelerator pedal?

The purpose of using a differential amplifier in this context is to accurately measure and amplify the small voltage differences that occur when the accelerator pedal is pressed. This allows for precise control of the accelerator pedal and ensures that the correct amount of voltage is sent to the engine.

3. How does the design of a differential amplifier affect its performance in replicating an accelerator pedal?

The design of a differential amplifier is crucial in accurately replicating an accelerator pedal. Factors such as the type of components used, the input and output impedance, and the gain of the amplifier can all affect its performance. A well-designed differential amplifier will have a high gain, low noise, and a wide bandwidth to accurately measure and amplify the voltage differences.

4. What are the potential challenges when trying to replicate an accelerator pedal using a differential amplifier?

One potential challenge is ensuring that the differential amplifier is properly calibrated and sensitive enough to accurately measure the small voltage differences. Another challenge may be reducing any interference or noise from other electronic components in the system. Additionally, the stability and temperature sensitivity of the differential amplifier must be carefully considered to ensure consistent and accurate performance.

5. Are there any alternative methods to replicating an accelerator pedal without using a differential amplifier?

There are alternative methods, such as using a potentiometer or a Hall effect sensor, but these may not be as accurate as using a differential amplifier. Additionally, these methods may be more susceptible to noise and interference, which can affect the overall performance and accuracy of the accelerator pedal replication. Therefore, using a differential amplifier is often the preferred method for this type of application.

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