Applying 12V signal to narrowband lambda input

[MalcolmG]

Hi there

I have an application where I need to measure a signal that switches between 0V and battery voltage depending on the state of a sensor (detects immersion in water). I have used a narrowband lambda input for this, which has a maximum A/D range of 6.098V - is it going to cause any issues if this channel sees 14V? The M1 ECU Hardware document specifies the channel has a no-damage range from -30 to +35V, but I want to be sure that other readings wont be affected by going over-voltage on the A/D converter.

I can use a voltage divider or zener diode to bring it into the range of the A/D, but I don't want to add one if it's not necessary. I have no other spare inputs or outputs that I can use.

Thanks

[Stephen Dean]

Hi Malcolm,

Does the signal just switch between 0V and VBatt+ and you just need to read the high and low values? Or do you need to read the transient voltages as well?

The UDig and Dig inputs are better for this if you have them available.

[MalcolmG]

It just switches between. If I had a spare digital input I would use it.

[Stephen Dean]

Hi Malcolm,

I would have to do some testing to see if it affected any of the other I/O in the ECU.

[AdamW]

Based on Marks comments in this post I would say not a good idea: viewtopic.php?f=66&t=4302&start=10#p19619

You could however just use a couple of resistors to divide your signal down to say 5V max

[MalcolmG]

Thanks Adam; I'd seen that post but re-reading it, it does seem pretty unambiguous that I just need to fix it - I was just hoping I might be able to avoid it. I haven't seen any problems yet, which probably just means they're waiting for a more critically important time to occur.

I think a simple zener diode between the signal and ground should be ok to clamp the output voltage <6V, slightly easier to fit and more easily hidden inside the connector.