If your RPM shows "dips" (sometimes jumping, usually to 0), use the latest firmware, at least [ 2009-10-12]
To understand more of the analog and rpm input, a schematic would really help.
- the RPM input is divided internally towards 5V, so about 0.6V on RPM input will be about 2.8V internally, equal the RPMref threshold.
- RPMref (often around 2.8V), can be changed with pulldown resistor to GND, or pullup to eg 4V
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
- 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.
- 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:
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
or whatever max RPM you find appropriate if 11000 is not enough. The last values are responsible for the color-"alarms".