I took the dashboard of a moped to my desktop, and I would like to make it think it's still on the moped with the motor running.
The RPM counter uses a pickup wire that is wrapped a few turns around the sparkplug wire and not connected to anything on that end, like a radio antenna wire. I would like to make a circuit to generate the signal in that pickup wire so the dashboard think it was a spark, to make the RPM counter show a value.
Writing the program is not a problem (basically it's just a Blink sketch with pulse frequency modulation), I'm just wondering how to do the electronic part of it. There must be a way to do it without using a high voltage, right?
I haven't tried anything yet, as I don't know much about electronic and I don't want to destroy the dashboard
Can you reverse engineer the circuit and create a schematic of the circuit? I just want to make sure there is nothing more than what I see in the picture.
The device labeled starting with S1M looks like a diode. It also looks like there is a via next to the cathode. Is that connected to anything?
I think you will be able to send pulses into the pickup wire to simulate the spark. It’s just a matter of determining how much voltage to use.
An alternating field (AC) will induce voltage into the pickup coil. So possibly you could try that.
Or a dc magnet on a rotating shaft.
Maybe would be to replace the coil with a resistor and voltage source that turns on an off.
Looking at that circuit it looks like a low pass filter with a resistor divide and rectifier so maybe voltage pulses in one direction comes out of that circuit.
I'm sure it's the full circuit, there is nothing more, and the pads next to the diode, and the ones next to R1 and the small white capacitor, are not vias, they are not connected to anything else, most likely test points. The big trace at the bottom is connected to one pin of the dashboard connector, and that pin is where the pickup wire is directly connected.
You could try a miniature 12v 0r 5v relay coil connected to the collector of a hall effect and tap off that to your D1.
Operate the hall effect with a small (3mm) diameter x 1.5mm magnet.
Your schematic does not show what voltages you are running so for this end it is just a wild guess.
@Railroader I was given the same suggestion on another forum (eevblog) so I will try that. But I'd like to do it in a non intrusive way, so if it works, the next thing I will try is to apply a 9V signal to the pickup wire and see what it does. Unless I'm mistaken, the voltage divider should make it safe to be read as HIGH by the MCU. I will try that when I'm at home.
Thanks for your replies
There is still something that I don't understand about this pickup wire in its normal usage. How to calculate the turns that are needed around the sparkplug wire to output a certain voltage ? Knowing that the spark voltage is something like 10000 to 25000V, maybe more (right?). If I do too many turns, will it pickup a voltage high enough that it could destroy the MCU ?
