voltage modification
voltage modification
(OP)
I've been trying to make a drive by wire throttle body work with a different model controller and am having an issue with developing a circuit as a work around. Please forgive me if I am way off base here as I am a mech. eng. and have very little electrical experience.
From what I gather when the throttle blades move the throttle positions sensors voltage should look like this chart:
http://chevythunder.com/TP%20sensor%20chart.BMP
When I move the throttle blades on the one I have both TPS 1 and TPS 2 follow a path similar to TPS 1. I think this is due to an internal redesign of the TPS. To work around this I figured I could make a differential op. amp. that would convert the TPS 2 output to equal the following equation so it would send the computer the signal it is expecting.
TPS 2 (to computer) = 5V - TPS 2 (coming out of throttle body)
I went to radio shack and bought the following:
(1) 742 op amp
(4) 1k ohm. resistors.
I connected them same as the circuit shown here:
http://en.wikipedia.org/wiki/File:Op-Amp_Different...
Pin 1 - not connected to anything
Pin 2 - TPS 2 signal voltage
Pin 3 - 5 Volt constant from PCM
Pin 4 - - 6 volt
Pin 5 - not connected to anything
Pin 6 - should equal (5V - TPS 2 signal voltage)
Pin 7 - + 6 volt
Pin 8 - not connected to anything
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/da...
So very simply I am trying to subtract one variable voltage from a constant one to give the expected reading to the computer. The circuit works but it is not giving the expected output voltage. Any help that can be provided will be greatly appreciated.
From what I gather when the throttle blades move the throttle positions sensors voltage should look like this chart:
http://chevythunder.com/TP%20sensor%20chart.BMP
When I move the throttle blades on the one I have both TPS 1 and TPS 2 follow a path similar to TPS 1. I think this is due to an internal redesign of the TPS. To work around this I figured I could make a differential op. amp. that would convert the TPS 2 output to equal the following equation so it would send the computer the signal it is expecting.
TPS 2 (to computer) = 5V - TPS 2 (coming out of throttle body)
I went to radio shack and bought the following:
(1) 742 op amp
(4) 1k ohm. resistors.
I connected them same as the circuit shown here:
http://en.wikipedia.org/wiki/File:Op-Amp_Different...
Pin 1 - not connected to anything
Pin 2 - TPS 2 signal voltage
Pin 3 - 5 Volt constant from PCM
Pin 4 - - 6 volt
Pin 5 - not connected to anything
Pin 6 - should equal (5V - TPS 2 signal voltage)
Pin 7 - + 6 volt
Pin 8 - not connected to anything
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/da...
So very simply I am trying to subtract one variable voltage from a constant one to give the expected reading to the computer. The circuit works but it is not giving the expected output voltage. Any help that can be provided will be greatly appreciated.





RE: voltage modification
Also, edit on the OP amp type it's a 741 not a 742.
RE: voltage modification
Secondly, you said that your supply rails are +6V and -6V. How are you getting these voltages? If you are generating them from the car's 12V power, make sure that your regulator circuits are able to handle the horrendous voltages swings that can be seen there. A load dump can put a high voltage on the line.
Be careful with this, because it could be really bad if this circuit fails in a full throttle manner.
Glenn
RE: voltage modification
As posted, the +6V, -6V power has some risks associated with it. You could use an opamp powered just by 5V, but then you need to make sure it is capable of rail-rail operation
RE: voltage modification
RE: voltage modification
Keith Cress
kcress - http://www.flaminsystems.com
RE: voltage modification
The 741 was preceeded by, at least, the 702 and the 709; and that's just the monolithic ones. The 702 and 709 were designed by Widlar, himself, and the 702 is supposedly the first actual monolithic op amp. Philbrick made the first solid state op amp.
TTFN

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RE: voltage modification
RE: voltage modification
Dan - Owner
http://www.Hi-TecDesigns.com
RE: voltage modification
RE: voltage modification
TTFN

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RE: voltage modification
RE: voltage modification
application for the UNO. The RC filter will work best with a very light load so an op-amp may be needed to buffer the output
of the RC filter. Of course this is old analog thinking. The UNO has pretty good drive characteristics and I would suggest
using a resistor of 470-620 ohms and a capacitor of 4.7uF to start for this 490Hz PWM. You have six A/D inputs and one of them
could monitor the output and adjust the PWM drive count to correct for losses. In worst case when a step function happens, a
calculated one cycle overdrive count could be added/subtracted to the PWM drive to give a better response. This will all take
some playing around if you are going for some extreme control. It takes a different way of thinking but it is far easier than
twisting a bunch of pots.
I would suggest that you take a running sample on the input signal to reduce noise and to create larger numbers to work with.
It is quite easy to work with a count of 5,000 to represent 5V. Makes it much easier to wrap your head around numbers like that.
Avoid floating point at all costs. Binary number limits like 255 and multiples will easily match up to 5V if you reduce the voltage
slightly to the TPS with a resistor drop.
5V is not 5V. Every regulator is different. One of the best features of the UNO is the serial USB output to a laptop. With that
you can display real time data on the screen. I built a fridge controller for my solar powered camp. Temp was calibrated dead on.
Worked great until I actually hooked it up to the fridge. The laptop powered the UNO at a slightly higher 5V than the on board
regulator of the UNO. That will change all your A/D slightly but noticeably. Had to open up the USB cable and cut the +5V wire
in order not to change readings.
RE: voltage modification
I set up the Arduino to take the TPS 1&2 sensor readings and convert them to the values the computer was expecting to see for a given TPS open percentage. I also added RC circuits after the Arduino and before the DBW computer to ensure the signal was analog or very close to it. Even though the output voltage was correct the DBW system did not work. Given this I'm going to ditch the DBW and go with a regular cable operated throttle body.
Thanks again to all who provided input.