Tech Forum

Subject: PDM35 V2 – floating inputs, LED glow and signal leakage after upgrade from PDM25

Hello Hardwire team,

I recently upgraded from a PDM25-V3 to a PDM35 V2 (firmware 1.4.0, configurator 1.4.0) on a FuelTech FT600 race car. Overall the PDM35 is a big step up (fast update rate, CAN start works instantly, much better logging), but I ran into several issues that I never had with the PDM25 and had to fix with extra wiring.

Setup:

- PDM35 V2, FW 1.4.0

- FuelTech FT600 + FT Input Expander on CAN

- LED tail/brake/side lamps

- Switch inputs are active-high (12 V switches)

Issues:

1) Floating switch inputs

With the switches OFF, the inputs read random voltages in the configurator:

Side_Lights 1.9 V, Left/Right turn 1.9 V, Low beam 3.2 V, High beam 5.6 V (very close to the 6 V threshold).

The "Pull Resistor" option is greyed out (None, not selectable) on these inputs.

Fix: I had to fit an external 4.7 kΩ resistor from every input wire to ground.

2) LED lamps glowing when the output is OFF

Brake and side-light LEDs glow faintly when their outputs are off. The PDM25 never did this.

Fix: external 1 kΩ 1 W resistor from each lamp wire to ground.

3) Signal leakage into the ECU input

I use a dedicated PDM35 HS output to send a night-mode signal to an FT600 input (no lamps on that wire). With the output OFF, the FT600 still saw enough voltage to switch night mode on. A 4.7 kΩ pull-down was not enough; only a 1 kΩ pull-down fixed it.

This suggests an off-state leakage / diagnostic test current on the HS outputs.

Requests / questions:

- Can the "Pull Resistor" (pull-down) option be made available on all digital inputs?

- Can you add a per-output option to disable the off-state open-load diagnostic current, for outputs driving LEDs or ECU signal inputs?

- Is there a recommended way to use an HS output as a clean logic signal to another ECU without external resistors?

I bought the PDM to reduce wiring, so needing about 15 extra resistors is disappointing. With these two options in firmware, the PDM35 would be a true plug-and-play upgrade from the PDM25.

I can provide config files, screenshots and logs if helpful.

Thanks,

Jocelyn Attard

Malta