Tachout (pin35) problem

[Paul_H]

I am attempting to use the tachout (pin35) function of my V2 Microsquirt (v2.886 code) to input a pulse to my wideband controller so I can display RPM on the display device. So far without success. I am not an electronics person but looking at the tach input circuit schematic

schm3.gif

tells me that when uS is powered up (without engine running) I should be able to measure 12V at pin 35 on the ampseal connector. I am not able to see this 12V and also I am unable to measure any resistance between pin 1 and pin 35 om uS. Could this mean that transistor Q1 is bad or that resistor R21 is bad or am I missing something here with regards to configuration or hardware jumpering.

[Paul_H]

Comments Anyone?

Where are Q1 and R21 located on the board? Can they be tested? Can they be replaced if faulty?
Any assistance would be appreciated.

[Matt Cramer]

I'm pretty sure it defaults to zero volts and switches that up to 12. You can try using it as a spare output port and see if you could turn it on and off at will with temperature signals or the like.

[Bruce Bowling]

Lets back up a bit - do you have this running on an engine or some sort of tach input arrangement? If you are not getting RPM into the micro (verify with MT or TS) then the output will be low - like Matt indicates. Let me know and we will work from here..

- Bruce

[Paul_H]

OK, yes this is on a running engine and other than still going through the tuning process, there are no problems with this installation. This bike is my daily ride and I could not be happier with the outcome of this project.Some background first. My aim is to provide an input to the Techedge 2J1 wideband controller for the purposes of logging and displaying RPM on my display device. I thought the output on pin 35 would have been a 12 V square wave which would have been perfect for inputting to the Techedge controller. So far I have not been able to get this to work and after guessing and assuming that the default state of the Q1 transistor in the tach input circuit was off, I should be able to measure 12V on pin 35 if uS was powered up. This was not the case, but obviously I could be way off the mark here.

[Bruce Bowling]

This output should be a 12V squarewave, so there is something going on. This signal is the equivalent to the "InjLED" signal on MS-II. I agree with the idea posted here to reconfigure this as a spare port output to verify the operation - you do this in the spare port configuration. Maybe set it to react to the coolant temperature and monitor the output with a scope. This would help pinpoint the root cause.

- Bruce

[Paul_H]

Bruce, thanks for your response. I'm afraid I don't have a scope but I went ahead and reconfigured the port anyway hoping that I could improvise to get some useful information.

untitled.bmp

I configured the port this way because 'rpm' is a real time variable that I can easily control to guage change and I wanted PM3 to be set 'Lo' when uS is power cycled so that transistor Q1 in the tach input circuit is turned off thus allowing the collector to be pulled up to 12V which I should be able to measure with a multimeter at ampseal pin 35. The result of this was 25 mV at pin 35, not 12V.
My thinking on this (as stated in the manual) is

if[(rpm > 1500) ]
then set the pin to '0';
else if [(rpm < 1500 - 50) ]
then set the pin to (1 - '0');
end if;

So after powering uS I should be able to measure 12V on pin 35. With the engine running below 1500 rpm there should be 0V on pin 35 and above 1500 rpm there should be 12V on pin 35.
The reality is 25 mV after powering uS, 65-70 mV with engine running below 1500 rpm and 100-110 mV above 1500 rpm.
I realise this a less than ideal (maybe even useless) way of working out what is going on here but you might be able to get something from it. If not please let me know if my logic on this is in the ball park and I will see if I can chase up a scope.

Paul