linear input/out from digitsal pot?

[strokedmaro]

Is it possible to (for example) to input 0-5vdc to a digital pot and have a linear output of 12-0? For example. a 2.5vdc input would have a 6vdc output...or a 5vdc input would have a 0vdc output? Thanks!

 

[Roff]

Is it possible to (for example) to input 0-5vdc to a digital pot and have a linear output of 12-0? For example. a 2.5vdc input would have a 6vdc output...or a 5vdc input would have a 0vdc output? Thanks!

The short answer is no.
This sounds like another one of those questions where you need to tell us what you want to do, instead of asking a specific question about your idea of how it might be done.

 

[strokedmaro]

The Idea would be to create a linear relationship between throttle body (car) position which produces a 0-5vdc signal and convert that to a 12-0vdc signal to control transmission line pressure.

The ECU uses multiple readings to determine line pressure (hydraulic pressure to clutches and what not) but their can be issues with tuning. Some people use a vacuum modulated setup to try and get a linear pressure (more vacuum=less pressure, less vacuum=more pressure) but this doesnt work really well for forced induction cars as vacuum changes with boost and who knows what other factors.

My idea was to be able to adjust my line pressure in relation to throttle position. (I would know that at 50% throttle my pressure would be "X") And would be very consistant. Just need a way to convert those voltages. Thanks for any help!

 

[Roff]

What does this 0-12V signal have as a load? Does it go to the ECU, or does it drive sme sort of pump, or... ?

 

[crutschow]

The Idea would be to create a linear relationship between throttle body (car) position which produces a 0-5vdc signal and convert that to a 12-0vdc signal to control transmission line pressure.

A digital pot requires a digital input. You have an analog input signal and want an analog out.

Seems like all you need is an inverting op amp with a 12/5 = 2.4 gain and biased with a +12V output offset. Thus with 0V in, the op amp's output is 12V and with 5V in, the op amp's output is 0V.

Depending on the load you may need a buffer amp at the op amp output.

[Soapbox on]
See. Now that it's better understood what you need, we can come up with better solutions.
[Soapbox off]

 

[strokedmaro]

A digital pot requires a digital input. You have an analog input signal and want an analog out.

Seems like all you need is an inverting op amp with a 12/5 = 2.4 gain and biased with a +12V output offset. Thus with 0V in, the op amp's output is 12V and with 5V in, the op amp's output is 0V.

Depending on the load you may need a buffer amp at the op amp output.

[Soapbox on]
See. Now that it's better understood what you need, we can come up with better solutions.
[Soapbox off]

Sounds like you know what your talking about...Ive looked at Op amps before but found that most were audio related. Am I mistaken?

The load for the 12-0vdc would be a solenoid that would drop approx 1 amp. I would have to make sure about the current. The solenoid opens "X" mount as voltage decreases..at 0vdc it is fully open (max line pressure) any other idea's?

It would also help if someone could drop a part number for an op amp that would work for my application so I can read the datasheet and figure it out a little easier. THANKS!!!!

 

[Nigel Goodwin]

Sounds like you know what your talking about...Ive looked at Op amps before but found that most were audio related. Am I mistaken?

Yes, opamps are an essential component in analogue computers (which is where they come from), using them in audio is just a bonus.

There are plenty of books about opamps, I suggest you get one and read it, you can't afford not to understand opamps since the 1970's.

Essentially they are (treated as) perfect components, giving infinite gain, infinite input impedance, and zero output impedance - none of this is true (obviously) but they are mostly 'near enough'.

 

[crutschow]

Let us know after you've read about op amps and we'll give you some further info on doing your design.

You may also be able to find some tutorials on the web.