Aux input on a switch. Mj lt V4.

parky1972 · Post by **parky1972** » Thu Dec 09, 2010 2:15 pm

Quick question.

I'm running a Megajolt V4 on a Zetec running a carb.
I have an engine temp gauge and a Lamda sensor.
The Lamda outputs 0-5v, so obviously I can't just switch from one to the other without disabling the resistor on the board.
My question.. Would there be any issues with installing a switch so I can switch between 0-5v input and ohms for the temp sensor?
At the same time, switching the map option and input lines from temp sensor to Lamda.

Jason.

NITROPIXIE · Post by **NITROPIXIE** » Mon Dec 13, 2010 1:23 pm

Parky

Yes you could do this but then you would have to change the values of the aux input. You would be able to observe a change but the value you have inputted for the AFR and CTS (Coolant Temperature Sensor) would be different and to get an accurate readout you would have to go into the software and change the values of the aux input, if you understand what I mean.

If you were not after an accurate readout on the configuation screen and just want to see a change in value then Yes, but if you wanted it to read e.g 80C (temp) and then 14.7 (AFR) then you need to change the values of the Aux input everytime you flicked the switch.

Hope this makes sense to you.

Ryan

parky1972 · Post by **parky1972** » Mon Dec 13, 2010 8:52 pm

Yes, I understand.

Basically, I'd need to change the calibration information every time I changed the switch.
It was more a 'can it be done' than 'is it practical'.

I'd certainly like to try both water temp and Lambda readings on the MJ JR V4 unit.
Atleast I can try both, and see if one works better than the other.

I suspose MJ2 would be a better option for something like this really.

Jason.

NITROPIXIE · Post by **NITROPIXIE** » Mon Dec 13, 2010 8:58 pm

Absolutely, MJ2 would be able to achieve this having 2 ADC inputs.

If you didn't change the calibration, you would still have the raw data there, you would just need to be able to change it into legible (easier to read) data.

parky1972 · Post by **parky1972** » Mon Dec 13, 2010 9:06 pm

No problem.

Ta.

Might give it a go then.

Jason.

NITROPIXIE · Post by **NITROPIXIE** » Mon Dec 13, 2010 9:17 pm

You will need to make some circuitry changes as the AFR will provide a 0-5v signal, where as a CTS is a passive sensor, so will need a voltage divider circuit to provide an output voltage also.

You could use the 5v TPS output of the MJLJ and a resistor to create a voltage divider circuit to provide a voltage out. If you want more details then I could provide a circuit diagram.

parky1972 · Post by **parky1972** » Mon Dec 13, 2010 9:49 pm

Erm..
I thought the only change needed was cutting the track at R8? (From memory.. Haven't checked..)
This was where I was going to wire in the switch.

I had looked at the possability of the TPS input.
But my Megajolt uses MAP.

I do have a second MJ unit that currently has TPS, but I intend on converting that to MAP also.
Actually, could that be switched in a similar fashion? Seems a shame to 'bin' the TPS function totally, where having it as a switched option might be useful for possible future upgrade.

Jason.

NITROPIXIE · Post by **NITROPIXIE** » Tue Dec 14, 2010 12:06 am

parky1972 wrote:Erm..
I thought the only change needed was cutting the track at R8? (From memory.. Haven't checked..)
This was where I was going to wire in the switch.
Still cut the R8 track as you are not going to be using the TPS input, only the 5v reference is required for a 5v regulated supply for the voltage divider.

I had looked at the possability of the TPS input.
But my Megajolt uses MAP.
MAP and TPS use the same input to the processor, you wont be using the TPS input for this modification if your using MAP

I do have a second MJ unit that currently has TPS, but I intend on converting that to MAP also.
Actually, could that be switched in a similar fashion? Seems a shame to 'bin' the TPS function totally, where having it as a switched option might be useful for possible future upgrade.
I think I am confusing you with what I am trying to state. Once I have come up with a circuit diagram hopefully all should become clear

Jason.

parky1972 · Post by **parky1972** » Tue Dec 14, 2010 2:32 am

It's Ok.
I think I'm confusing the situation here somewhat by talking about two seperate things.

Jason.