Jimstim tach circuit question

[suprant0010]

I've been little by little getting my MS ready to go in the car. I wanted to test my hall sensors out, so I figured I would do it with the Jimstim.

I zeroed the rpm pots out and then wired my hall signal up to the tach pin on the Jimstim, and the ground and 5v supply to their appropriate pins. I powered up my MS with the stim, and my crank sensor seems to be working good. I have a healthy rpm signal when I rotate the pickup wheel.

The sensor works perfect when its routed in through the stim, the problem is when I run the MS directly from a car battery. The MS syncs up and all my sensors work that I have wired in, except for the Hall hooked up to the crank input. It will no longer show teeth logging for that sensor. I tested that there is 5v current on the ground and supply wires going to the sensor, and I've tested the signal wire with an LED.

What is the stim doing to my Hall signal that I'm not getting from directly hooking it up? I thought it went directly to pin 24 on the db 37. Maybe some kind of pull-up resistor on the Stim board, although I don't really know what a pull-up resistor is for? I've read that some hall sensors require a pull-up resistor, but my hall signal going to the cam input on the MS3X plug works fine without any kind of resistor.

[SymTech Laboratories]

It's very possible that you need to add a pull-up resistor. Most Hall effect sensors have an open-collector output; some have internal pull-up resistors but others don't. The MS3X input has a pull-up resistor that is usually enabled by default (JP7). Try adding a 1k - 2.2k ohm resistor between pin 24 and 5V.

[racingmini_mtl]

Depending on which jumpers you have on the JimStim, you may have a 12V or 5V pull up resistor on your Hall sensor when connected to the JimStim. That means you'll need a pull up resistor on your Hall sensor. The assembly instructions do mention where to connect it.

Jean

[suprant0010]

It's very possible that you need to add a pull-up resistor. Most Hall effect sensors have an open-collector output; some have internal pull-up resistors but others don't. The MS3X input has a pull-up resistor that is usually enabled by default (JP7). Try adding a 1k - 2.2k ohm resistor between pin 24 and 5V.

It makes a lot of sense, the only thing that gets me is why does my cam input on the ms3x card work with the same sensor without a pull-up, but the main board input does not?

Depending on which jumpers you have on the JimStim, you may have a 12V or 5V pull up resistor on your Hall sensor when connected to the JimStim. That means you'll need a pull up resistor on your Hall sensor. The assembly instructions do mention where to connect it.

Jean

Now that you mention it, I do remember setting that jumper. I just never understood the purpose until now.

[SymTech Laboratories]

It makes a lot of sense, the only thing that gets me is why does my cam input on the ms3x card work with the same sensor without a pull-up, but the main board input does not?

The MS3X card has a pull-up resistor on it. Take a look at it; if jumper JP7 is in place, the pull-up is enabled. The main board, however, does not have a built-in pull-up resistor.

[suprant0010]

Awsome, thats exactly what I needed to hear...Thanks for the response guys