Weirdness With 12V Connected To Analog Input

[kbuckham]

While I do understand that the analog inputs are only useful from 0-5V, I understood they were safe to use voltages higher than that. I was using a switch on my dash that activates my methanol injection system and to kick off the RCP logging on Analog input 5.

As soon as this input goes high, all the other analog inputs get erroneously high readings. It seems that this ~14V (alternator outputs about 14.4V) signal is flowing through to the other inputs. If this is the case, you might want to make a note about this. In other devices that I use with 5V analog inputs, a voltage higher than 5V but less than about 40V simply reads as full scale on the input, but doesn't negatively affect other inputs.

In addition, once I removed this signal from analog input 5, my RPM input has quit. I double checked my wiring tonight and I confirmed continuity and my dash tach still works so the signal is the same as it was before. Either the extra voltage on the analog input was making that input work, or I have fried my pulse input 1. (The ECU signal is supposedly a fairly clean 12V signal used by the ECU to monitor RPM and feeds the dash tachometer.) When I have time tomorrow I will reintroduce 12V signal to the analog inputs to see if my RPM monitoring comes back.

[brentp]

Hi kbuckham,

Thank you for the note. We will investigate on our end and make a note as necessary.

Can you try to connect the switch so that it switches the 5v reference from RCP into the analog input instead?

Also, you can also set the GPIO in input mode and connect it that way as well, saving an input.

For your RPM input, you can also connect it to one of the other RPM inputs for comparison.

Please keep us posted as to what you find out.

[kbuckham]

Hi kbuckham,

Thank you for the note. We will investigate on our end and make a note as necessary.

Can you try to connect the switch so that it switches the 5v reference from RCP into the analog input instead?

Also, you can also set the GPIO in input mode and connect it that way as well, saving an input.

For your RPM input, you can also connect it to one of the other RPM inputs for comparison.

Please keep us posted as to what you find out.

Thanks, I have moved to using a GPIO for enable/disable logging from my methanol injection switch. (I use a combination of my methanol injection "arm" switch and significant acceleration to kick off data logging.)

I *could* switch the 5V reference, but I really don't want any extra wiring, as the methanol injection wiring is already quite complicated. (It enables a secondary fuel and timing map in the ECU via an input pin, enables the boost control solenoid, and enables the methanol injection pump relay.)

My RPM input is still dead, so I'll move that to the second input, but I'm a little concerned I might kill that input as well. My car is getting an oil cooler upgrade, so I won't be able to test until this Sunday assuming I don't cause any odd leaks.

[brentp]

A tip: you can loop back a PWM output from the terminal block and direct it back into one of the timer inputs. You should see a reading in the sensor monitor. If you have time to do this, let us know what you see.