MoTeC Global Forum

best way to wire this in to a PDM for electronics shutdown prior to disconnect ?

https://www.cartekmotorsport.com/wp/wp- ... ctions.pdf

It seems to output an enable signal, +12v during normal operation. Going to 0v when the disconnect has been activated which it will do for 0.5s prior to full disconnect.

Just connect it to a standard PDM input as "active high" and link to the output for the ignition coil and/our ECU power feed so it is only active with true. If already activating via another input (eg ignition switch) then you will need to make a new function using the current input AND the input from the cutoff switch.

Or

Set it as "active low" on the input and add it as the "Master shutdown channel" (Global Setup -> Output pins -> Master Shutdown channel) and make sure that Master shutdown is enabled for the ECU and/or ignition coil outputs.

Yes...I have exactly the same cutoff switch and was literally just look at the manual for it today to double check current ratings!

Thanks.
but it seems at odds to page 5 of the manual ? which seems to suggest it is not happy with 12v direct inputs ?

"Input Switch Connected to Battery
When an input is driven from a device that switches to battery, the switch
should if possible, be rearranged so that it switches to 0 V.
If the signal comes from an electronic device such as an ECU that has an
output that can only switch to battery (e.g. a signal that indicates when to turn
the fuel pump on), this might not be possible. In this case an external pulldown
resistor is required. The resistor should be 1500 ohm 0.25 watt and
should be connected between the input pin and the 0 V pin.
The input trigger levels should be set to 4 V and 5 V to guarantee correct
triggering for all possible battery voltages."

That will work fine into a PDM input as it actually pulls to ground when turned off rather than just floating/disconnecting.

The only time you need pull down resistors is when you have things like simple toggle switches that supply 12V when on and are just disconnected when off. With no path to ground, the PDM input just floats at some voltage close to 12V and so it can't determine whether the input should be on or off.

adrian wrote:That will work fine into a PDM input as it actually pulls to ground when turned off rather than just floating/disconnecting.

The only time you need pull down resistors is when you have things like simple toggle switches that supply 12V when on and are just disconnected when off. With no path to ground, the PDM input just floats at some voltage close to 12V and so it can't determine whether the input should be on or off.

Good stuff.