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== RPM and wheelspeed input ==

Beware that using the RPM input might require input voltage threshold adjustment with a simple pullup / pulldown resistor in some cases, depending on input voltage level. It is easy, but not plugandplay in all cases.

=== RPM input HW ===

rpm_input measures 5V if left open

* connect the signal input here

rpm_gndref to adjust voltage threshold with pullup/pulldown resistor

* Devices with serial_nr >= 100 have appr 0.6V threshold by default that is suitable for the common voltage level thresholds (notably VR / HALL / logiclevel) without pullup/pulldown resistor applied to rpm_gndref.

** pulldown (eg. 100k to GND) for lower voltage threshold (hardly ever needed)

** pullup (eg. 510k to +12V for higher voltage threshold): might be needed in very rare cases when the negative peak of the input signal is higher than +0.55V, like: 2V / 10V squarewave input signal.

* devices with serial_nr < 100 measures 2.5V on rpm_gndref input if left open

** if the zero-crossing negative edge is to be detected (standard VR sensor, eg. typical magnetic wheel-speed sensor or 60-2 wheel), leave it open.

** if you want higher threshold, eg. for a 0V / 5V HALL sensor, connect rpm_gndref with a 220k pullup resistor to a 5V (or 510k to 12V)

=== RPM input config ===

Known as "RPM settings" in megatune.

* rpm_toothcount. The number of pulses per crank rotation.

** 02 for a 4 cyl 2 events per rotation

** 3a (decimal 58) for a 60-2 wheel

** or 23 (decimal 35) for a 35-1 wheel

** set with (Man)mttg19c.. like mttg19c02 or with MegaTune

* rpm_multiplier

** set with (Man)mttg1amttc.. like mttg1amttce5 or with MegaTune

** 229 - 0xe5 default for RPM display. Different value can be used to cheat, or for vehicle-speed.

The precision is 1 RPM. Note that display from 230 .. 15999 is possible. Above 9999 the first digit is hexa, so

* a845 (=10845 RPM)

* b231 (=11231 RPM)

* c000 (=12000 RPM)

* d888 (=13888 RPM)

* e792 (=14792 RPM)

* f999 (=15999 RPM)

* fffu (above 16000 RPM)

For wheelspeed input

* set rpm_multiplier=FF (255) first, than adjust according to shown value (calibrate)

** Or you can calculate from the pulses / km.

** example: 10 pulses / m = 10000 pulses / km

*** => 1km/h = 10000 pulses / hour = 166.67 pulses / minute (to be displayed as "0001")

*** with tooth_count=0xa7 (decimal 167)

*** and rpm_multiplier=0xe5 (decimal 229, same as used for RPM)

To support 1 pulse per cam-rotation: experimental [doubleRPM-firmware]

* rpm_toothcount=1, rpm_multiplier=229 needed for 1 pulse per camrot.

* rpm_multiplier=114 for rpm_toothcount pulse per (crank-)rotation.

=== RPM tricks ===

* don't forget to adjust toothcount according to the trigger pattern (pulses per rotation)

** if displayed RPM with toothcount=01 is half of real, see double-RPM experimental firmware that supports 1 pulse every second crankrot (1 every camrot). Normally it shouldn't be needed

The sensing voltage-level-threshold is adjusted with RPM-gndref pulldown/pullup resistor (yes, soldered; not configurable in software) value. Depending on the input signal specs, you might not need to connect RPM-gndref at all (eg. for 5..10V amplitude AC signal). The round device will not be harmed if you first try with RPM-gndref not connected.

First measure DC voltage on the output RPM signal (that you want to measure) when connected to nothing, but engine running.

Measure DC voltage

* between GND and the RPM-input pin. With nothing connected expect 4.8 .. 5.2V.

* between GND and RPM-gndref pin. With nothing connected expect 2.4 .. 2.8V

** if the voltage is below 2.6V, you likely need pullup resistor (old standard)

** if the voltage is appr 2.8V, you don't need pullup nor pulldown in most cases. Low amplitude VR-type signal might become more stable with 100..270k pulldown resistor (pulldown means between RPM-gndref and GND).

Mega Tune Setup

RPM gauge range (max RPM) can be increased in round.ini file, change the line:

<code>

tachometer = rpm, "Engine Speed", "RPM", 0, 8000, 300, 600, 3000, 5000, 0, 0

to

tachometer = rpm, "Engine Speed", "RPM", 0, 11000, 300, 600, 3000, 7000, 0, 0

</code>

or whatever max RPM you find appropriate if 11000 is not enough. The last values are responsible for the color-"alarms".

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