electrical help?

I have been looking for a CHEAP pressure sensor that can output a variable voltage based on positive pressure. But all I have been finding are $100 plus sensors or cheap sensors that only put out a single voltage. I then want to send that signal to a motor contoller to vary the speed of a pump. What code words do I need or where do I need to shop to find the right parts?

air pressure or physical pressure/force? For physical force - BI model 404 from digikey ($18.00 - runs on 5v - proportional output relative to button position) or try a search term of position sensor.

Try here? If not, just have fun poking around:

http://www.sciplus.com/

Here's one from Omega for $75: http://www.omega.com/ppt/pptsc.asp?ref=px137&Nav=preb02

In reply to oldtin:

Air pressure

Now that I think about it, does it make sense to run another wire from the MAP sensor ECM signal to a motor controller (PWM?) and running the motor off of that?

This is for a alcohol/water injector. Currently I am using two nozzles with solenoids and etc. to make a 3 stage system and it is complex and kludgy with a bunch of sensors to cut boost to spring pressure.

I keep thinking that there has to be a better way to get this done cheaply.

EDIT: Now I am looking at turbine flow meters. Can I run the MAP output voltage and the flow meter voltage through a comparator (like a lm339n)? Then if the flow is below a certain level (clog) or above a certain level (leak) compared to the MAP voltage the boost control solenoid cuts boost pressure to wastegate spring pressure. I am thinking about leds to signal low flow and high flow errors along with the current low fluid level warning light. I am also wondering if I need to switch from a solenoid to a check valve to prevent back flow with the new arrangement.

If any EE types can help with some guidance I would forever be grateful.

Don't forget, you have less pressure at WOT. So you would need something that works inversly,more voltage at less pressure.

In reply to iceracer:

This is a turbo Subie motor. I tried showing my ideas to my engineer wife and she immediately started designing a hugely expensive bomb-proof high precision highly redundant control system.

Watching this closely. I've been considering a water injection for my volvo.

Do you want infinitely variable or do you want a step style sort of thing? As in 0-5psi = no meth, 5.1-10psi = some of the meth, 10.1 - eleventybillion psi = all the meth.

HKS makes map sensors usually used for their tuning boxes/ecus that have variable output like what you're looking for. Can usually find them on ebay for $50 or less. As to whether or not it's exactly what you're looking for, i'm not real sure. I'm not quite that savvy with this stuff.

In reply to 92CelicaHalfTrac:

I have a three stage water/alcohol system now and that works pretty well. Basically at a certain psi nozzle 1 is activated, next step nozzle 2 is activated and 1 is inactive, last step is both are activated.

I was running thses ideas past my wife and she mentioned that the nozzles might not atomize at a lower psi. So I tested it out and at 20 psi I get drops of water spraying out and not finely atomized like I need.

So what I think I need now is fast pulse interrupting style solenoid valve so I can maintain constant pressure. I have no idea where to find one of those for cheap.