I have designed and created two systems that are currently present in a small race-car.
The first one is a circuit to control the fans of the car. The topology of the system is the following: Battery -> Master switch ->Fuse box -> Relay -> 3-way switch When using the switch, the first mode is to let the ECU (DTA s80) control the fans and the other is to turn the fans on constantly (through the relay).
The second circuit is the electro-pneumatic system that controls the two double 3/2 pneumatic valves responsible for the gear changes. There are two parts in this system. First there is there is the pneumatic part. I am using two valves (one for upshift/downshift and one for the clutch). These valves are controlled by the second part of the system which is the electrical. They are connected via individual cables to a PCB that has as an input two buttons coming from paddles from the steering wheel.The principal of operation is that both pads to whom the cables are connected have always +12V and when an input is detected, the micro-controller (STM32F103) outputs a signal to an analog circuit that grounds one of two pads so that the valve can "see" 12V. Between the fuse box and the PCB there is an on-off switch.
Now there comes a problem. Both circuits work fine except one critical moment. When I have the switch for the PCB to the on position and the 3-way one is either on mode 1 or 2 and I turn the fans off, the upshift valve fires to the piston. Note: These two system are not crossing each other in no point (in fact there are on separate sides of the vehicle).
So far I have disconnected the steering wheel (still problematic) and I have external harness in order to see if there is a wire cut somewhere (still problematic) as well as disconnecting some or all the fans to not have any power draw from them (guess what, the problem is still there).
Does anyone have any idea why there is such a weird behavior ?