# Modifying a feedback signal

Discussion in 'The Projects Forum' started by 275kv, Nov 3, 2012.

1. ### 275kv Thread Starter New Member

Nov 3, 2012
3
0
Hi,

I'm trying to workout how I can modify the signal coming from a position sensor to change it's characteristics. I have attached a graph that shows the current output and the output desired. I expect I should be able to achieve this with a a few op amps but have so far been unable to work it out. Any ideas?

• ###### Sensor.pdf
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Last edited: Nov 3, 2012
2. ### ScottWang Moderator

Aug 23, 2012
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995
What you have the circuit?
What is the problem of that circuit?

3. ### 275kv Thread Starter New Member

Nov 3, 2012
3
0
The sensor is part of a throttle body on a diesel engine, it's sealed unit. My goal is to design an interface unit that will modify the V returned to the ECU (as shown int the graph) so that the throttle body will respond differently - just between 1v and 4v as the graph shows. As yet there is no circuit, just the idea, hence my questions. Ideally I would like to build a circuit that has Vin = Sensor V and a Vout = Modified Output

4. ### ScottWang Moderator

Aug 23, 2012
6,427
995
You have to separate the voltages to 4 sections, and detect them.
1. To keep the original input voltage when less 1V from the position 0% to 20%.
2. To keep the voltage at 1V from the position 20% to 60%.
3. The voltage increasing from 1V to 4V from the position 60% to 80%, this section should be have a base value to do the adjust from 1V to 4V, maybe it is a some kind of rising rate.
4. To keep the original input voltage from the position 80% to 100%.

When you get the 4 parts as above, and then assembly them become the output, that is your modified output voltage.

5. ### 275kv Thread Starter New Member

Nov 3, 2012
3
0
Thanks - almost there. What do I use to choose the lower of two inputs and then pass this voltage to the output. i.e. if A= 2v and B = 4v output should be 2v, if A=4v and B=3V then the output should be 3V.