This page is mostly obsolete, see InputTrigger instead

Rest of the page is mostly historical obsolete.

Sensors and mounting:

The HALL sensor needs a magnet too. We should add these magnets to the WebShop (since they are available; should it be 1 Euro?):


These already have the magnet:

On GenBoard/VerTwo you need to make a small connection for the input trigger on the board:

You need to connect the output signal of the opto (inside the board!) to the IC3 signal (pin 9 of the avr, available on 1x1 header J8). INT6 input was used originally, but we changed to use the IC3 pin for the primary trigger, because it has hardware-capture capability (more precision), and reserved INT6 for the secondary_trigger (CAM signal for dual-trigger applications, or measure alien ignition advance).

Look here:

The wire needs to go from the R18/C13 junction to J8 (the pin closer to the AVR). The physical place on the board is just to the right of the AVR. I used the lead of R18 (close to C13) to solder the wire on, then soldered it to the J8 header. There is no need to cut the trace to AVR pin 8 unless you need to measure alien ignition. If you already have a pin header in the J8 location, it is NOT recommended to desolder it. Many times damage occurs from trying to desolder. If there is no pin header in that location, you can just solder the wire to the pad.

Both the primary_trigger and the secondary_trigger on GenBoard/VerThree can be configured (independently) to accept any commonly used type of trigger signal.

See InputTrigger/AnalogSide for the amazing wide range of the chosen LM1815 circuit.

Inputtrigger can use any technology as long as you can acquire a ttl level signal in the end:

It's important to have clean signal from the inputtrigger sensor,especially when using ignition.

See [ various crankshaft sensor waveforms]


See MembersPage/MichaelKristensen/CamHallSensor for a custom HALLsensor installation.

To get a clean signal:

This is good:


Look on MembersPage/ChrisGerhardt/ChrisNotes for his HALL wiring and noise experience. He went through a great deal of ground noise issues and with everyones help seems to have a very clean trigger now.

See [for distributor hall sensor waveform]

HALL sensors:

The commonly used HALL sensor is a unipolar digital output (with histeresys) switching at appr. B = 4..10 mT [TLE4905L], as in our WebShop [shop].

Developers, please check these out, which would be useful:

HALL SENSOR TLE4905L (INF) DIGITAL TEMP COMP UNIPO this is the most commonly used type: low B threshold, but relatively high histeresys.

HALL SENSOR SS443A (HWL) DIGITAL TEMP COMP UNIPOLA I have a few samples of these, just tell me if you wanna try (in WebShop order TLE4905L and write SS443A in the order note). Looks like higher operating B, but smaller histeresys (11.5 / 14.5 mT) than TLE4905. Guaranteed upto 150C.





One more choise from Allegro: A3240 unipolar HALL, 4.2-24V [see more]

Optek OHB900, hall fork for vane type trigger wheels, This was reported to be inconsistent at high temperatures. -J�gen

Magnet and mounting

Forget Neodimium magnets in the engine bay, they become unreliable sligthly above 80C (!!!). Also, Neodimium magnets corrode as soon as the Ni cover is scratched. They are more expensive than simple ferrit magnets, and the extra strength is not needed. What is needed is good way of mounting. The easiest way to get a good signal is to have the magnet and the sensor on opposite sides of the (ferromagnetic, windowed material) wheel. However, this way of mounting is often non-trivial if space is scarce.

VR - Variable Reluctance

The output amplitude of a variable reluctance sensor depends on RPM. It will make appr. 100 times bigger signal at 6000 RPM than it makes at 60 RPM cranking. To suppress noise at high input levels while still allow to trigger on lower signals an adaptive hysteresis circuit is utilized using a peak detector.

Look at InputTrigger/AnalogSide for more details on solutions, particularly our favorite LM1815 chip.

See GenBoard/Manual/VrSensor/Polarity

Crank/cam trigger types and engine operation modes

The final input-trigger answer is to have cam and cranktrigger as


GenBoard has the IO and clocktics resources to handle both cam + crank inputtriggers at the same time. Handling multitooth trigger with the resources in GenBoard was not hard.

You can make a cheap timing light for your GenBoard:

Connect 5..7 high-power (narrow-lightcone) red LEDs in series, connect anode to +13.8V, and control catode with NPN and a 2 Ohm current-limiter resistor.

Also good for verification of your config :-)

Alien ign logging

Since camshaft-angle-control is implemented (for more than 1 cam), using third trig position is the obvious way to measure/log alien ign.

See also:

Here are 2 good printable degree wheels that might help someone get their project going when it comes time to setup their crank trigger.


[Degree Wheel 1]


[Degree Wheel 2]

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