Is it possible to take a channel that reports RPM and change it into plain ol' volts? Specifically, I have a 'fan speed' channel that reads a hall effect sensor, but it has a +5v supply and returns a 0-5v signal which the ECM/OS then turns into a RPM number. Can that be bypassed somehow (transformed?) to display the raw 0-5v reading (which could then be transformed again to whatever format required for whatever sensor)?
Nope. A hall effect sensor doesn't output a linear 0to 5v signal, it outputs pulses of either 0 or 5. The raw value would really be a frequency, that is converted to rpm.Originally Posted by blindsquirrel
Ah, but I don't want to read the hall sensor, it's been removed (mechanical fan). But the input at the ECM is just sitting there doing nothing, and spare inputs on an E40 are non-existent. I want to use that pin to read a normal linear 0-5v something, for logging in the scanner only: permanent WB install, or a pressure sensor.
I don't know if the hardware in the ECM is able to do that, or if the OS is hard-coded to do the freq-to-RPM conversion, or if there's a transform that can be applied in VCM Scanner to display the new sensor as volts instead of a RPM value (which would be... wait, could that work anyway, if the ECM hardware on that pin allows it?).
I may plug in a potentiometer across those fan speed pins and see what the RPM reading displays as at various settings.
The only way it would work is if there is a separate Voltage parameter, similar to the MAF sensor. I think HP Tuners would need to enable it in the scanner if the PCM is even capable of looking at it any way other than 0 or 5.
Not that it really matters, I'm just curious now if the ECM is reading actual frequency to derive the RPM value or if it's looking at an average voltage over some period of time and then doing a conversion. The EV fan system is not exactly a high precision/accuracy thing like the CKP. The diagram just shows the signal input at the ECM with an internal pulldown resistor, then from there it heads off to who knows where, some undocumented magic happens, and then 'RPM' comes out the other end.
I like your thinking on using the input for something else, but I really think it will be reading a frequency. As you mentioned you can check it with a pot pretty easily.
To make it happen with not much work you could use an arduino to take the voltage reading from your 5v sensor and then convert that to a frequency the pcm is looking for, then create a user math parameter to convert that back to a voltage... Not a streamlined setup but it would give you the ability to log in hp tuners an extra input.
Actually, I have used an Arduino before to monitor TPS/boost/WBO2 thresholds and then activate a pneumatic solenoid to control a Holley carb power valve in a blowthrough application...
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