Im looking to control (open and close) a ground circuit that will see up to 15 amps 12VDC, where the trigger to open will be any voltage above 0.02 VDC, and close the ground path when the trigger signal is at or below 0.02VDC
Application for background.
Automotive cooling fan clutch. It is controlled by the PCM though closing the electric clutch's ground signal.
A common modification for this vehicle is to wire up a simple switch and aux ground path circuit that allows the driver to manually ground the circuit, which causes the clutch to fully lock up. This has been done for more than 20 years, it works and has shown no issues at all with the PCM or clutch.
For my own needs, I only need the clutch fully locked when the vehicle is at idle. Fully locking the clutch improves AC system performance when the vehicle is not moving.
If I can build an Arduino based device to read a 5DVC reference voltage accelerator pedal sensor voltage (0.00 VDC at idle) that closes a relay (the ground path for the clutch) and opens the relay at or above 0.02 VDC (really anything above 0.00, but figured .02 VDC gives some headroom in signal noise) This would allow an automated control of the ground signal at idle, and allowing the PCM to control the clutch ground signal at anything above idle
An automated system of what we do now with a manual switch.
A: Is this feasible using Arduino and or other common products?
B: What is your recommended build to accomplish the goal?
I've purchased an Arduino education kit so I can start to learn the code processes
Thank you in advance for any assistance you may have
20mV is pretty darn little in a noisy environment with high currents. What's the highest threshold you could get away with? Something like 2V would be more reliable if that's feasible.
Anyway, you could use an opamp comparator circuit and couple that with a suitable logic level N-channel MOSFET. You may want to include a little hysteresis so you don't get any chattering between on/off in a threshold situation.
No Arduino needed, but you can use one if you want. It's overkill though.
Thanks for the input.
so my initial question used book values for sensor voltage. I just measured and found this particular truck reads .84 at idle ... (or 4.0 VDC on accelerator sensor 2, which drops in voltage with more pedal travel..Its a check sum for the PCM) and at a few MM of pedal travel it was at 1.21 VDC ( sensor 2 at 2.78 VDC)
So Id like to have the ground signal path closed at say 0.50 and less, open at 1.25
D1 and R1 create a reference voltage of around 700mv, which is within your 0.5-1.25V trigger range.
U1 is used as a comparator and compares this reference to the input voltage from your pedal (or whatever it is exactly; I'm not familiar with it).
R2 and C1 form a delay that prevents the output from chattering as I mentioned earlier. This signal (node R2/C1) is used as an input for the other half of the dual 8606 opamp, again used as a comparator, this time at an arbitrary 0.5VCC (2.5V in this case). The output switches M1.
The 'switched GND' output is at the drain of M1. I've put in R6 as a hypothetical load resistor; this is where your...'whatever it is that burns 15A' goes.
I've used 8606 and the MOSFET type quite arbitrarily; you could (should) use an actual comparator in place of 8606 and the MOSFET should be one that (1) matches your current requirements, (2) will turn fully on with a 5V signal and (3) should be easily available.
This is a quick sim of the behavior, using a slow (0.1Hz) sine wave as the input (green trace):
Note how the current through the load (I6) drops to zero about a second after the input voltage drops below the threshold voltage.
You could put on some bells & whistles to make all this more resilient against whatever contingencies you want to take into consideration. The basic concept should work though.
There's many additional ways you can do this of course.
