Temp guage for car

[myp71]

I was wondering if any of you had any ideas about somehow hooking up a temp gauge on my car without switching out the old sender unit? I don't want to change the sender unit because its in a plastic intake

[Chris Smith]

You can buy radiator hoses with sensor mounts and sensors in them. They have a vulcanized patch with metal threads. <p>If you have to cut and paste it into your old hose, you might have to do that, or if you have a straight run??

[dyarker]

Is there a temperature gauge on the dash, or is it just an over-temp idiot light?<p>If idiot light, you might have to change the sender.
--------------------------------
With a linear sender where the voltage goes lower for higher temps; you would need an op amp to invert and scale the voltage, an analog to digital converter, and binary to seven segment decoder/drivers.<p>If you can program a PIC, then one PIC and 10 transistors (for 3 digits) replaces all that stuff.<p>Cheers,

[myp71]

The guage on the dash reads low norm high kinda thing.I would just let to tell what its actually at in degrees.<p>Thanks <p>Ryan

[poseidonx]

Here are two ideas,
The first one is using a thermometer
measure the water temp in the radiator
versus differnt readings on your gage
mark them at different intervals and
then just make yourself a different face
for the gage.
The second one is using your exsisting
sending unit measure the temp like before
but measure the different resistances
at every 5 to 10 degrees ive seen on the
net where people have used a 555 timer
witch is connected to your sending unit
or thermister and using a pic count the
pulses and in code associate them with
the temp.I will try to find you some links
later today.

[Dave Dixon]

Be careful trying the thermometer idea. The
system works by having the fluid under pressure
as a closed system. High temp = high pressure.
Dave

[Engineer1138]

I'll second what DaleY said, but add that DigiKey has digital LED panel meters around $40 or so if you don't have PIC/microcontroller programming tools available.<p>Have you checked out what this would cost from JC Whitney (www.jcwhitney.com) or the like? I've bought a lot of cheap car parts from them over the years and they may have exactly what you need.

[Dave Dixon]

I have an LM34 (Fahrenheit) and a LM35 (Centigrade) Precision Temp. Sensor from National.
See the datasheet here...LM34 Datasheet
It is simple to hook up for analog or digital apps. I guess you would have to offset the
output, as you can't immerse it within the radiator
fluid. I would expect a linear relationship between the fluid, and a chosen metal place where
you would bond the chip.
Chips are yours for the asking. Give me a mailing address offline if you like.
Dave

[Will]

You should be able to get the correct temperature with an LM 34 or 35 - Just find a metallic tube or connection which is carrying the cooling water - you can do it at the radiator inlet. Stick the LM 34/35 to the metal and then wrap some form or insulation, old rags etc around it. That should find about the correct temperature. If I were doing it I would use two LM's i.e. one on the radiator (Top) inlet and one on the outlet - use a selector switch then you have a good guide to how the cooling system is working.

[poseidonx]

The tempature of the water doesnt change under
pressure the boiling point of the water changes.
that is why the system is under pressure so it
doesnt boil at a lower temp.tempature is tempature regardless of pressure!

[poseidonx]

I wanted to add something to my other post.
I am not saying open the radiator cap when the
engine is hot but take the cap off when the
engine is cold and let the engine warm up
to its normal operating temp and while
its is doing this take your measurments.
using a thermometer like this is used by
mechanics checking to see when the thermostat
is opening when there is a rapid change (hotter)
thats when the thermostat has opened.

[myp71]

<p>
Thanks a lot for the help! <p>I think I might go with the lm34 idea I have a metal pipe on the cooling system because I bypassed by heater core so That would be great just to put the ic on the pipe.<p>One question how does the read out work/connect and how hard will it be to get/build one?<p>Thanks again for the help <p>Ryan

[hp]

The LM34 outputs 10mv per degree F. This means all you would need is to connect the output of the LM34 temp sensor to the input of a panel meter.<p>Just make sure to feed regulated 5volts to the meter and the LM34. Also make sure that your dc power is clean since automobiles have horrible electrical noise and spike problems.<p>Harrison<p>[ August 25, 2004: Message edited by: hp ]</p>

[Dave Dixon]

In a precious post, I left the link to the datasheet for the LM34. I have ONE each LM34 and ONE each LM35 in the package I can mail you free.
You can experiment with one (let the smoke out),
and use the other tweaking for final design.
I understand about the pressure/temp thing. I just didn't want anyone red-lining their temp, and
popping the cap too fast!! Good luck,
Dave
BTW the datasheet shows how to hook up for analog, and
several digital type outputs.

[myp71]

Will~ <p>
Thanks for the great e-mail! I really understand it more now.<p>Thanks a lot!<p>Ryan