I'm and auto mechanic. I'm working on putting together a sensor simulator for car sensors. Using the cars charging system of 13.8v i used a 8v (7808) voltage regulator, resistor as a voltage divider, and a potentiometer to make a 0-5v signal. this can be used to fool many car sensors. Then with a switch and a different voltage divider i can make a 0-1v signal for fooling oxygen sensors.

i thought it wold be convenient to add a volt meter right on board so i don't have to hook up a bunch of leads. i found the pmled 9v. with a post i found in these forums (the Post) I got the display configured. (the documentation is abysmal at best) i also added a 9v (7809) voltage regulator to my circuit board to power the display. when i hook everything up, the display shows 1, their equivalent of OL. if i use a 9v battery to power the display it works great.

there effectively is no documentation on the pmled. everything that i found is on the 7107 chip that runs the device. From what i have read if you hook up V- and IN- together you short the reference voltage to ground and with no reference the display will show OL. The REF LO, COMMON, and IN- are all hooked together.

If it's possible how can i use the cars charging system to power the display using the 9v regulator? (using a 9v battery seems waist-full when already hooking up to a battery)

Stuff i read. (mostly didn't understand)
7107 data sheet
Do's and Don'ts of Applying A/D Converters
Low Cost Digital Panel Meter Designs and Complete Instructions for LCD and LED Kits
Tips for Using Single Chip 31/2 Digit A/D Converters

 

Fooling the Sensors?

Most sensors are typically NTC resistors, with the obvious exception of the TPS (throttle position sensor) and MAF (Mass Air Flow).

If your looking to fool the NTC sensors, use a heating device, as their resistance decreases when they get hotter.

Your description tells me your trying to fool the ECU.

Are you fooling the ECU for troubleshooting purposes? If so, replace the NTC sensor with a fixed resistance to ground.

Do you have the part number of the sensors your trying to "fool"?

 

yes I'm fooling the ECU for trouble shooting purposes. its a great diagnostic tool for testing mass air flow sensors, manifold absolute pressure sensors, fuel tank pressure sensors and a host of potentiometer based sensors like throttle position and fuel level. also it allows you to verify if the ECU is in fuel control and if it's logic is ok. but i have that all done and it works. (i have a variable resister tester for NTC type sensors already)

what i'm asking is how to power the 7107 chip in the pmled with the car battery and let me test the voltage i'm making? (like hooking up both negative leads and positive leads to the same battery and get a reading of that battery)

If i use a separate 9v battery everything works but i want to power the volt meter with the car so i don't have to have a battery inside the case.

 

This should do it for you:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=102-1510-ND
It's an isolated DC-DC converter; accepts input of 9v-18v DC (22v max)

Don't cause a load dump (like turn a heavy load off such as the headlights, honk the horn, etc) while you're using it, or you may burn it up.