86CamaroSC

I want to build a circuit that turns on a warning light when the voltage drops below about 10V. None of the orginal dummy lights work and my car does not have a computer anymore. I want to put in a few of my own circuits for warning lights. Anyone have a schematic for a circuit to do this? Thanks in advance for the help.

Tim Burgess

See the following post for a low fuel level indicator circuit schematic:

https://www.thirdgen.org/messgboard/...ML/000867.html

The same circuit may be used as a low voltage warning indicator if the 10 volt zener diode is replaced with a 1N4735A 6.2 volt zener diode (Radio Shack part number 276-561). Also, connect pin 4 of the LM339 to two 10K resistors, instead of the fuel level sender. Connect one of the 10K resistors to +12 volt ignition power (pin 3 of the LM339), and connect the other 10K resistor to ground (pin 12 of the LM339). Set the low level reference voltage adjust pot to 0.5 * the voltage you want the circuit to trip at; set the pot output voltage to 5 volts, if you want the circuit to trip at 10 volts. You may calculate the new delay value using 6.2 volts as the trip threshold, instead of 10 volts, and reduce the capacitance if you want to decrease the indicator turn on delay.

Tim

JPrevost

Can this be used for high temp warning? How about a shift light? Those are the only 2 other things I would LOVE to make. A shift light would be great. Tim thank you SO much for this info, saved me lots of money doing it myself .

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, Jon (350 TBI!)
91 Red My website

Vader

JP,

A high temp wanring will require some sort of temperature sensing element (like the secondary fan sensor). Unless you wanted to build a lamp driver circuit (???) you can simply connect the warning lamp or LED to the sensor itself.

You could use an OP AMP and feed a comparator to interpret the analog signal from the CTS used for either the gauge or ECM, but the scaling would be pretty experimental.

As for the shift light, your ECM should already be equipped with a shift lamp driver if you have a manual trans. If you want a shift lamp to signal operation of a manually shifted automatic, you'll need to monitor TPS, RPM, transmission selector position, and VSS, then introduce conditional logic, and operate the lamp when your chosen parameters have been satisfied - just like the factory.

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Later,
Vader
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"Fear is how I fall, Confusing what is real..."
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JPrevost

I'm thinking about just using a stock fan switch to tell me when the car is overheating, this will turn the fan on at ~205 and I will have a 180 thermo in soon (160 now). As for the shift light, what are you talking about? I just want an rpm activated switch. Nothing fancy, just like the MSD products, except I plan on using a few small LEDs instead of a lamp.

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, Jon (350 TBI!)
91 Red My website

Tim Burgess

Here's a schematic for a high temperature warning circuit:

<IMG SRC = "http://albums.photopoint.com/j/View?u=1554272&a=11793907&p=49807005">

It's at http://albums.photopoint.com/j/View?...907&p=49807005

Tim