module vr discrete

Here we have rusEFI own VR decoder based on https://github.com/mck1117/vr-interface

THRESHOLD_VR needs a PWM output directly from the MCU, not through output module.

Optional VR_ANALOG if routed should go to ADC3

See https://github.com/rusefi/hellen121vag/issues/60

At the output of the U753B, the voltage difference between the VR inputs is limited to a range of approximately minus 1..6V plus 2.5V (Vref). U754A together with U755 generates a short positive pulse at the output when the output of U753B exceeds Vref, i.e. when VR+ becomes bigger than VR-.

Similarly, U754B and U756 generate a pulse when the voltage on VR- is greater than that on VR+. To provide hysteresis after the pulse is generated, Vref is replaced by thresh_low and thresh_high, so small fluctuations around zero of the voltage difference VR+ and VR- do not lead to false alarms. These pulses switch the RS flip-flop from U752 and U757, i.e. after the event VR+ > VR- at the output "0", and after the event VR+ < VR- at the output "1".

U753D and U753C with strapping filter the PWM signal from the processor and set the thresholds thresh_low and thresh_high based on its duty cycle.

The U753A acts as an "amplifier" for the 2.5V received from the resistor divider to provide a stable VREF voltage.

The system will not work with a Hall sensor, because. if one of the lines is grounded, the signal from the Hall will not cross 0V, since the difference between the Hall signal and ground will never be negative and will never cross 0V. Nevertheless, you can connect VR on one wire, and ground the second at the input to the ECU, since the signal on the remaining VR line will cross the 0V voltage, but there seems to be no reason to do so.

The simulation project repeating but not precisely the original scheme in the Proteus Design Suite: https://github.com/andreika-git/hellen-one/blob/master/kicad/modules/hellen1-vr-discrete/vr-discrete-simulation.pdsprj