Cam-HALL inverter - subpage of InputTrigger/AudiTrigger
Cam-HALL signal is used to mask one of the 2 crankhome pulses.
It has little significance normally. But with the special 7A flywheel that has 2 notches, the HALL signal polarity gets important. VEMS listens when the processor sees a 5V signal, and neglects any crankhome-VR pulses when the processor sees 0V signal. With the more usual "mostly 5V" HALL sensor the cam-HALL inverter is installed between the input pin and the processor: it helps filter out the VR noise from the 7A flywheel (and other noise too).
As MembersPage/DesmondAudi shows, at least some of the AAN engines are equipped with "mostly 0V" HALL sensors. In such cases the ECU should NOT have the cam-HALL inverter.
"mostly 5V" HALL sensor: (cam-HALL inverter is good !)
- HALL sensor output measured with DVM (DC voltage mode, engine running), measures >3V (3.5..4V typical)
- if engine is not running, rotate the engine by pushing the car in gear 5. The HALL sensor measures >3V most of the time, and goes near 0V for short periods of time
"mostly 0V" HALL sensor: (cam-HALL inverter actually makes it more noise-prone !)
- HALL sensor output measured with DVM (DC voltage mode, engine running), measures <1V (0.4V typical)
- if engine is not running, rotate the engine by pushing the car in gear 5. The HALL sensor measures <1V most of the time, and goes above 3V for short periods of time
- cam-HALL inverter is standard since 2008-06. With "Mostly 5V" HALL sensor, the inverter results in small "listening window" around the 62 BTDC-cyl1 crankhome pulse. This eliminated cranking and/or 7000-9000 RPM falsetrig/triggercut experienced with some flywheel/trigger input bias combination.
- original solution had no cam-HALL inverter, that meant huge listening window around 134 BTDC cyl5 pulse. It was prone to noise with some installs (depending on flywheel and trigger input bias) during cranking and/or high RPM (around 7000-9000 RPM)
For [Audi 7A flywheel] that has some notches that disturb the crankhome-VR signal, an inverter is needed to neglect the big window around 134deg BTDC cyl5 (and keep the small window around 62 BTDC cyl1).
![[Audi 7A flywheel]](http://www.theswansonfamily.us/modules/gallery2/v/marc/work_0/efiexpress/vems/crank_triggers/5cyl_flywheels/IMG_1167.JPG.html){kind=link}
The inverter can be an NPN transistor such as TIP31 or BC817 (almost any NPN transistor that can handle 10mA and 20V)
- emitter (gnd) connected to ground (EC36pin26)
- collector (output) connected to ECU cam-HALL input
- which is EC36/13 if the inverter is outside the box
- or the PCB side of the cut EC36/13 pin if the inverter is inside the box
- or an onboard pad on v3.6
- 2k7 .. max 10k pullup resistor between +5V (EC36pin28 or pin29) and NPN base
- HALL sensor output connected to NPN base.
- which is NOT EC36/13 if the inverter is outside the box! just the base pin of the chosen transistor
- the connector side of the cut EC36/13 pin if the inverter is inside the box
- EC36/13 pin on v3.6
Cam-HALL inverter is essential for 7A flywheel, and recommended for all InputTrigger/AudiTrigger installs. Mention the audi engine-harness type AAN/ADU/ABY or 3B or 7A in the order note.
Operation with failed cam-HALL sensor ("limp-home")
The factory audi cam-HALL sensor is known to break relatively often, especially old (original) sensor in an overheated engine bay, especially the sensor in the distributer (the sensor at the front, as in some engines, seem to fail less often). We've seen small unipolar HALL-sensor [SS443A] hacked into the distributer but we don't know how difficult it is to apply it reliably.
The motronic cannot start with a failed HALL sensor. VEMS can start with failed HALL sensor, appr. 50% of the time (need to crank a few more time if backfires), if:
- (with cam-HALL inverter, which is standard now, with trigger_tooth=00) the HALL pin is pulled to ground. In other words, to limp-home to the car-electrician, find the pin in the HALL connector that is the +5V from ECU, and connect the other 2 pins
- without cam-HALL inverter (which used to be standard before 2008-06, with trigger_tooth=08) the HALL pin is pulled to +5V (simply disconnect the sensor connector; note that with some luck the HALL sensor will fail with output stuck to +5V or open circuit).
Verifying if my controller has camHALL inverter or not
Note:
- If it's sectrig=HALL, than it does not have, by default.
- sectrig=auditrigger if motronic55, or EC36 but specifically asked for "audi application or cam-HALL inverter" in order note, has camHALL inverter by default.
But you can easily verify:
- If you have camHALL inverter
- with input open (remove connector), there should be no spark at all.
- you need to pull camHALL input to GND (remove connector, and use small wire or component-leg between signal and GND. Not between 5V and GND please!) so all pulses go through (all pulse, not every second means worse cranking startup sequence, ~limphome mode)
- If you do not have camHALL inverter
- when pulled to GND, there should be no spark at all.
- you can leave camHALL input open so all pulses go through (all pulse, not every second means worse cranking startup sequence, ~limphome mode)