Automotive sensor

I am designing a pic based project to intercept the dc voltage produced by an automotive sensor and re-produce the voltage seen by the car's systems but controlled.

The sensor produces a voltage between 0 and 10v but if the value is between 6 and 7v the car must see only 6v.

I envisage a pic with a/d sensing the input voltage via a voltage divider to bring it down to 0 to 5v. The pic then decides what to do and outputs the voltage again using a dac.

The problem is how to get the voltage back up to level without adding component cost.

I thought of using an op-amp to double the output voltage but is there a better way? Do any pic's operate at vdd=12v?

Thanks all.

Ooooooh that smells of some cut-off bypass in here :D

Some PIC have built-in shunt regulator, look the HV serie (12HV615, 16HV616 etc).

I doubt you need a DAC, a smoothed PWM out OR r2r network should do the trick.

Sounds interesting. If you don't mind me asking, what part of he cars system is the subject here? I might be able to help. Iv been a GM auto technician for 17 years. I have some experience tricking linear sensors.

This was a response from a pm that I sent to David that I thought I would post in case someone has something to add or take from this. Or maybe if You've been monitoring this topic for updates.

"Okay,
Well, A Landrover is a far cry from any General Motors product :) however I’ll do my best to help as much as I can. Although Cadillac did build a car that had alot of German influence. The Cadillac Catera.

It seems that the service information catalog I normally use only list information for Landrover gasoline engines. I have no idea why. However a quick search online showed that there is some information available if needed. I haven’t had the time to look through it though.

First thing is first. Let’s cover some of the basics. Assuming your Landrover is newer than 1996, then your Landrover will be fitted with an OBDII Fuel management system. What this means is tricking or sending different readings to the ECM is going to be tough to do without setting a check engine light or causing the engine to run at a default value regardless of what parameters your sending to it. There are ways around it though. Let me explain what I’m talking about.

The ECM will monitor the air flow readings from the AF sensor and compare them to a software algorithm set up usually in the eeprom of the ECM. The reason for having this is for the ECM to have a way to perform test of the engine components with software. So let’s say at idle with 0% throttle angle and 15% engine load, the ECM receives input from the AF sensor of 4.5 g/sec. If the ecm algorithm is set to read normal conditions between 4.2 and 4.9 g/sec . then no fault will occur. But if we changed that reading to be Lower, Let’s say 3.9 g/sec then the ECM would compare this reading to the algorithm and this reading would be out of range. A fault will be stored and might turn on a check engine light. Most manufactures will provide a default value for the ECM so normal operation can continue. It’s basically a baseline of parameters that the ECM needs to continue running.

So long story short. If you skewed the AF parameters you MAY NOT really accomplish anything because the ECM will since a fault and revert to a default value.

Like I said though, there are ways round this. And the best answer is to access the eeprom data and change the algorithm. This is basically what the programming kits that you see for sale in racing magazine, and speed shops are selling. As far as accessing these files of the ECM, Unfortunately I can’t help you with that. That’s one of the things I’m here trying to learn too. Along with other projects that have nothing to do with cars. So hopefully this is your strong point and we can help each other out on this project.

So basically before we can do anything on this project we need to learn the basic operation of how the AF system works on that Landrover. Like if the ECM will revert to a default value and if so then what are the ranges for those values. Also what parameters are being monitored by the ECM to decide if its out of range."

Moved from Schematic.

Robert