View previous topic :: View next topic |
Author |
Message |
freefuel
Joined: 27 Aug 2007 Posts: 55 Location: New Jersey, USA
|
Posted: Tue Oct 23, 2007 7:57 am Post subject: reading automotive temp sensors. |
|
|
Has anyone here tried using thermal sensing resistors? I'd like to read two or three of these sensors in an automotive environment.
As far as I know the body of the sensor is connected to the car ground, and the gauge is just a glorified ammeter.
Justin _________________ The only difference between science fiction and reality is about 60 to 100 years. |
|
Back to top |
|
|
ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
|
|
Back to top |
|
|
freefuel
Joined: 27 Aug 2007 Posts: 55 Location: New Jersey, USA
|
|
Back to top |
|
|
freefuel
Joined: 27 Aug 2007 Posts: 55 Location: New Jersey, USA
|
Posted: Tue Oct 23, 2007 11:54 pm Post subject: |
|
|
Has anyone tried using this thermistor chip from maxim?
http://datasheets.maxim-ic.com/en/ds/MAX6691.pdf _________________ The only difference between science fiction and reality is about 60 to 100 years. |
|
Back to top |
|
|
cloudnine
Joined: 29 May 2007 Posts: 58
|
Posted: Wed Oct 31, 2007 7:22 am Post subject: Automotive sensors |
|
|
Just browsing and saw the word "automotive" that's me !!!!! Do i presume you are attempting to use the sensors already fitted to the vehicle. Now there are so many varibles depending on the make and model of car. Ealier models used a NTC type temp sensor (temp goes up resistance goes down) but NOT necessarily with a constant current flow. The sensor would go to earth - yes- but with a pulsed positive supply (12v 0v 12v 0v) via the temp. gauge in the car. The pulse was derived from a bi metalic strip all rather crude and 'noisey' but thats all there was in the 70's and 80's. As time progressed the bimetalic vibrator was replaced with a 5v reg. or similar varients. More modern times automitve electrics have become "less noisy" and temp gauges have regulated voltage supllies and easier to adapt to perhaps the ADC of a Micro. Resistance would vary from about 0 ohms (hot) to 2,3 0r 400 ohms (cold) sorry there is no nominal amount and as you will see one needs to be faily accurate to get a succesful outcome and this will depend on the make and model of car. To interface the FUEL sensor in most but not all cars they tend to use a variable reistor with a float on it moving up and down and the SAME voltage/ current issues apply as per the temp gauges. Additional issues with the fuel sender are the facts that as the fuel splashes around so does the floart and hence the resistance is all over the place. In old cars the bi metallic vibrator would smooth this out and modern cars an "average' is taken over X period of time to stabilize the dash board gauge. Well I trust that has helped you further. |
|
Back to top |
|
|
freefuel
Joined: 27 Aug 2007 Posts: 55 Location: New Jersey, USA
|
Posted: Thu Nov 01, 2007 5:50 am Post subject: |
|
|
The purpose of the micro controller is to automate and monitor a waste cooking oil conversion in diesel vehicles, and add several gauges the car is lacking. (oil pressure for example in the early VW TDI.)
The specific vehicles I have in mind are the 1996 and up Volkswagen TDI diesel, and the 1981 thru 1985 Mercedes 5 cylinder 300D series, and 86 to 87 (but not the 1988 model) 6 cylinder Mercedes turbo diesel cars.
Using the factory sensors would be nice, but I originally intended to use VDO senders (because they are available in metric sizes), as they are the OEM supplier to both manufactures.
For the fuel sender I only want to monitor the second tank for the WVO, so an aftermarket VDO or Autometer sender would be used. (the sender is primarily for preventing an overflow of the tank during the purge cycle of the system.)
Justin _________________ The only difference between science fiction and reality is about 60 to 100 years. |
|
Back to top |
|
|
freefuel
Joined: 27 Aug 2007 Posts: 55 Location: New Jersey, USA
|
Posted: Tue Dec 04, 2007 8:11 am Post subject: using the ADC as an OHM meter? |
|
|
I thought of a simple way to measure the resistive temp sender with a series resistor to give a 0V to 5V output from a 12 volt supply, but if the sensor is disconnected from the AVR 12 volts will be connected the the ADC pin via the resistor. is there a simple way to fix this? maybe with a zener clamp diode? _________________ The only difference between science fiction and reality is about 60 to 100 years. |
|
Back to top |
|
|
|