I am building a K dashboard tester powered by an ESP32.
For almost all signals, it is either a ground signal, or a 12V signal, so just have to translate 12V to 3.3V digital signals, and vice versa.
But for the speed, i fail to to generate an adequate signal. I know the sensor is a passive hall effect, which sends a relatively small voltage to the dash circuitry ( about 250mV ?)
All my tests with ESP32 IOs ( PWM signal, DAC output) do not make the needle moving....
I have tested with Caramba and my computer header output, it works....

My question is: does anybody already emulated a speed sensor with an Arduino, ESP32 or other microcontroller ?

How strong is the output from the ABS sensors?

I don't know is this would help but it might:
Speedo Healer

The output from the VR sensor is about 1V - 2V peak to peak sinusoidal.  I think 250mV is too low.  When testing my TGPI boards, I use a function generator outputting a variable frequency sine wave of 2V p-p between 5Hz and 100Hz and it drives an after market speedometer just fine.

49BMWK1 wrote: I know the sensor is a passive hall effect

What is meant by this description?
I ask because I think of Hall Effect devices as being active.
That is, they require a voltage feed, and have 3 terminals:  Voltage in,  Ground and Voltage out.

An inductive pickup could be described as a passive sensor. It has no voltage feed, but generates a pulse from its coil when a magnet moves near it.

you're right with the description of an active Hall effect sensor.  the speed sensor in the rear drive of the K-bike is variable reluctance.  It does not need a voltage supply to activate it so it is passive.  It uses the principle of reluctance (magnetic resistance) to induce a current in a coil which has a toothed wheel revolve under it.

robmack wrote:The output from the VR sensor is about 1V - 2V peak to peak sinusoidal.  I think 250mV is too low.  When testing my TGPI boards, I use a function generator outputting a variable frequency sine wave of 2V p-p between 5Hz and 100Hz and it drives an after market speedometer just fine.

thank you for the information.

I tried with the DAC signal from the ESP32, which can output from 100mV to 3V.
I can see the signal with the oscilloscope, but it doesn't fire the speedo.

As it works with an headphone output from the computer or from a mobile, with about 100mV peek to peek, i suspect an interfacing impedance problem ?

Maybe there isn't enough current drive in the EDP32 to trigger the speedometer amp in the K100 cluster. Maybe add an emitter follower circuit after the DAC output to see if that helps.

robmack wrote:Maybe there isn't enough current drive in the EDP32 to trigger the speedometer amp in the K100 cluster.  Maybe add an emitter follower circuit after the DAC output to see if that helps.

i have two different solutions:
 - adding an amplifier
- building a signal moving under and over zero, as it looks to be with the sender...

If your output is swinging between 0V and 100mV (instead of +/- 50 mV), then feed your DAC output through a series 0.1uF capacitor to average out the positive offset.

All along, I've made the assumption that you are testing the BMW OEM dashboard because you mentioned Karamba. Is that a correct assumption? It's never been stated explicitly so.

robmack wrote:If your output is swinging between 0V and 100mV (instead of +/- 50 mV), then feed your DAC output through a series 0.1uF capacitor to average out the positive offset.

All along, I've made the assumption that you are testing the BMW OEM dashboard because you mentioned Karamba.  Is that a correct assumption?  It's never been stated explicitly so.

yes it is an OEM BMW K dashboard tester....

I have resolved the problem with a capacitor and a resistor... which make a +/- 3V signal instead of a 0 /+3V
Now i am able to drive the speedo.

Fantastic news!