Jeremy contacted me to say that he wanted his MHD fortwo to start with the MHD
turned off, therefore giving him the opportunity to turn it on if he wanted. He then
went and designed a rather neat and compact solution to the problem.
Consisting of 7 cheap components, a small piece of vero board and 3 short pieces of wire. It
is easily small enough to be stowed underneath the existing switch to keep the original look.
You can splice into the wiring if you like but you can push the wire ends into the back of the connector and secure for a less permanent solution. With the circuit fitted, the car starts with the MHD turned off but the standard switch still works as intended allowing you to toggle the MHD on and off as normal. If you toggle the ignition on-off-on quickly then the car will start with the MHD on.
Resistor R1 = 12R, 0.25W
Resistor R2 = 1M, 0.25W
Resistor R3 = 1M, 0.25W
Capacitor C1 = 1uF, 63V (low leakage)
Zener Diode ZD1 & ZD2= 15V, 0.4W
Semiconductor Q1 = ZVN2106A (N-type mosfet)
Jeremy also points out that even if this circuit is incorrectly made or wrongly fitted, it will not damage the car. So, if you can solder and know where to buy the components you will probably have the knowledge to recreate this circuit on vero board for your own MHD Fortwo should you need it.
Thanks to Roberto who had issues with this design and recommended the 2nd diode.
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