I am using an Arduino Mega to control features of the kit car I am building. One of the things I want to is have a switch to turn on the coolant fans indepentent of the Sniper wiring. The fans are controlled by a relay that is taken to ground. I figure if I splice a wire into this circuit between the relay and the Sniper I can run that to one side of the switch and then run the other side directly to the Arduino so that when there is current I will get a high signal. I will then turn on the indicator LED to show that the switch is on. How do I do this, I think the built in pull up resister is not correct in this case but I am not sure, do I need to put a resistor in line. Coding and wiring help is needed.
It is a similar case with the leds the power is supplied into the LED and then the ground will be controlled by the Arduino how do I set this up to only go to ground when I want it to?
I am assuming since you did not define it this will be a vehicle put on the road. Here are a few things you may want to read.
does the sniper wiring refer to: "Holley Sniper EFI FUEL INJECTION system"? Remember this is an electronics forum so many of us are not familiar with terms like this.
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STMicroelectronics Application Note AN2689:
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Yes this is for a car that will be on the road, and yes sniper is the Holley sniper efi system.
The electronics are not very advanced I am doing more advanced stuff. The arduino is mounted on vibration mounts. I can take a look at some of these so,e will not apply like the OBD as it is not a production car.
What's a Sniper?
Heard of Humber Snipe.
For those of us not familiar with kit cars, a bit more information always helps.
Do you want to know if power is getting to the fan, or is the fan turning with power applied?
@jpgale
Can you clarify? Do you want to activate the cooling fan relay independently of the ECU or just indicate with an LED that the ECU has activated the cooling fan?
@jim-p i will run the headlights via a relay with the arduino so best to be safe.
@EmilyJane I would like to be able to operate the cooling fans independently of the Sniper ECU and only have the indicator light when I have activated that switch and no indicator light when the ECU turns on the fans. I also want to change the color of the indicator light when the headlights are on hence why I can’t just wire the indicator light into the switch itself.
Thanks for the clarification. Will there be a possible condition when the cooling fan will be activated by both the ECU and by the Arduino and if so will you want to indicate that that has happened?
Also, will the non-ECU activation be operator controlled via some sort of manual switch or will the Arduino do the control based on some event that it measures or senses other than by the operator?
Sorry @jim-p I misunderstood, yes I could avoid the arduino but that does. It give me what I want.
@EmilyJane it is operator controlled via a latching switch. When the switch is on the indicator should be lit. If the ECU activates while the switch is on the LED should be on. The LED is basically and indicator the switch is on.
Simplest method is to use a 2nd fan relay in parallel with the current one, so that either relay being activated will turn the fan on. That avoids any connection to the ECU, and in the worst case failure would result in a constantly running fan.
In that case you have the option of just controlling the action with an operator controlled switch and sensing that by the Arduino with a circuit like in post #18, although I would put the relay in parallel with the ECU relay as suggested in post #17OR having the Arduino control the relay and the LED based on the Arduino sensing the position of the operator switch. The second option allows you to implement any additional action you might want with respect to the fan control if that appeals to you.
Thanks all, I will go with the switch sending a signal to the Arduino and have that operate one of my spare Sainsmart relays which can then take the fan to ground and run it. However I was not planning on using the Optocouplers as it will all be from the same power source is the optocoupler necessary in this case. I don’t have a lot of room for additional circuit boards but can find room it is it necessary for all the inputs.
I am also going to make a drawing to ask more about the voltage protection I will add that to a new post once I have done it.
