First Time Project, Sequential Delay & Temp Sensor

Community Projects
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Hi I am looking for some assistance in designing a PIC microcontroller board for use in an automotive project with the following objectives:

The circuit board should be located in an enclosure with a faceplate containing one manual on/off switch and three LED indicator lights, mounted on the dashboard. The board should have input from three on/off solenoid valves and a temperature sending unit, all located in the engine compartment. The valves are 3-port 2-way fuel valves, 12VDC <2 amps each. The temp sending unit is a standard automotive type, which goes from a fuel line to an electric gauge mounted on the dash. The board should function in the following way:

Manual Switch is ON:

If temp sensor is > 160F, then Valve 1 is ON. If Valve 1is ON, Valve 2 & 3 are ON.

If temp sensor is < 160F, Valve 1 is OFF. If Valve 1is OFF, initiate delay sequence.

Delay sequence: Valve 2 wait 0-120s turn OFF, then Valve 3 wait another 0-120s turn OFF.

Manual Switch is OFF:

If Valves were ON, initiate delay sequence. If board receives power with switch in the OFF position, do nothing.

Board should be wired to ignition key.

I am very little experience, but I hope this project is within my reach. Is anyone willing to help me figure it out? Thanks in advance!

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  1. Get an Arduino or some other small microcontroller board and learn to program it. Do simple stuff like blinking an LED at different rates depending on what switch you push. Then move on to reading temperature sensors and outputting their values.

  2. Now that you have that experience, start considering this project. Nothing you ask is difficult: read one digital input, one analog input and control three outputs. But if you are starting from ground zero, then it’s a steep learning curve. Take baby steps

  3. Why does it have to be a PIC? There are easier to use chips out there

  4. Once you have done enough of (1) so you understand how to program for I/O, then learn about protecting automotive circuitry. That should keep you busy for a bit. There’s a great appnote called “Suppression of Transients in an Automotive Environment” that goes into detail about the stuff you have to worry about.

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Thanks for the reply. It doesn’t have to be a PIC if there is an easier way to do what I need. I am not super interested in tinkering around for months in a roundabout way to completing my project… I think I can leap past the initial blinky LED hurdle. If someone can give me some concrete directions on what components I need or what specific tutorial to read, I would be most excied to do some advanced tinkering.

A few more specific questions:

Automotive temp sending units are variable resistors in the ground side of a 12VDC circuit that leads to a temp gauge. Would it be possible to share this signal with a controller? How? What do I need to get the signal down to what an Arduino can interpret? If it steps down to <5V range, will noise become a problem with wires running several feet into the engine bay?

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I found this blog post with a wiring diagram… http://www.darfieldearthship.com/2011/1 … board.html

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Re: the temp gauge … so it runs 0 to 12v (? or is that 15v ?) ? What’s the scale factor, deg/volt ? What’s the 160 voltage ? Or is really just a variable resistor, controlling the current through the temp gauge ? (How old is this car ?) Are the valves 2 wired, is the - wire electrically isolated from the valve body ? Or are they just 1 wire, meaning you must switch “12v” to the valve ?

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My question is…what’s the purpose of these valves and the delays?

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I’m guess he’s switching btw diesel fuel and waste vegetable oil. What I don’t get is whether the 0-120s delay needs to be adjustable on-the-fly or is just a preset, fixed number that’s not known ATM.

Also when the OP says …

Manual Switch is OFF:

If Valves were ON, initiate delay sequence. If board receives power with switch in the OFF position, do nothing.

Does this mean that if the Manual Switch was ON and the valves were ON but then the car was turned OFF (power removed from controller) and then the Manual Switch set to OFF prior to turning the car back on ... that the valves should stay ON even when the temp < 160 (Manual Switch is still OFF = do nothing) ??