JP3 jumper pullup

[gullwingmd]

I am new to this forum. This is my first post. I am building a MS3 with a MSX board. I am a physician, I am a very good mechanic however I have never built a CPU before and apparently I am out of my depth here. I am at "JP3 is a jumper for a pullup on the "Tacho output". So I have no idea what this means. Do I somehow wire it to my tachometer?

JP7 is a jumper for a pullup on the "Cam" input. I am using a Ford Cam sensor. So what does that mean? Do I attach a wire to it? Do I leave it as is? I asked tech support for help and got a non-answer.

[jsmcortina]

Your sensors are always connected to the external wiring harness.

Fit and forget the "tacho" jumper.
Whether you need JP7 installed or not depends on the type of cam sensor you have. Read the Hardware Manual for your product and the section on cam sensor wiring.

James

[gullwingmd]

Okay. I have spent all the last few days reading every post I could find on Megasquirt assembly. I found a post explain what a "pull-up resister" does. Yeah, I am learning. The article then sends me to pages in the hardware manual explaining how, if you use a Hall sensor, you will need to add a resistor into the circuit and then attach it to a 5 volt VREF on the prototype board. This is good. I'm not sure why this information isn't in the ASSEMBLY instructions but okay.

When you say "fix a jumper and forget it" that presumes I know what a jumper is. I don't, hence the problem. Is it a short piece in wire connecting both holes? There is one picture in the hardware guide showing a jumper but sorry it is hard to make out. Is it some sort of clip that pushes into the two holes?

I have an aftermarket Tachometer. No idea how it works. So I put a jumper across JP3?

I have a Cam angle sensor taken from a small block Ford. It is a black plastic device fitted into what would have been the distributor drive. I doubt it is a Hall device. I can hook a VOM to it and spin it but even then I am unsure how to interpret the results. This particular Cam angle sensor wasn't shown in the guide. If it is a Hall effect unit I am supposed to somehow add a 100 ohm resister and then wire it to either a 12 volt power source or 5 volt VREF source? If my cam angle sensor isn't a Hall effect type then do I put a "jumper" at JP7?

then JP8 is a pull-up jumper for Nitrous In. I am not using nitrous. Can I ignore this?

[billr]

This is a V3.0 mainboard you are building? Then a "jumper" is just a piece of wire connecting two solder pads; sometimes just a bit of bare wire, sometimes an insulated wire. How many pins on the cam sensor, 2 or 3? A 2-wire is almost always VR, and 3-wire Hall. Where are you located? There may be a kind soul nearby willing to give you some in-person help in starting to learn this stuff.

[dontz125]

The JP3 jumper for the tach output is also on the 3X card, and is two vertical pins to be bridged with a little black cap (should have been included in the box with the 3X card). When the cap is installed, a pull-up resistor (already on the card) to 12v is connected to the circuit. Assuming the tach in question wants a 12v square wave signal, then yes - install the jumper cap.

JP7 and JP8 are the same idea as JP3. Assuming you are connecting your cam sensor to the 3X 'CAM' pin, JP7 is used if the cam sensor is a Hall device; it is NOT used with a VR sensor. JP8 is used when the 'Nitrous IN' pin is connected to a typical going-low ground switch; it is not used with the sort of going-high switch arrangement used with a nitrous rig.

[billr]

Indeed, "jumpers" are quite different on the MS3X or V3.57 mainboard. Sorry if I confused the OP here...

[gullwingmd]

I apologize for not providing this; I have a megasquirt 3 with MSX board. I will be running sequential ITBs and COPs. My crank uses a Hall sensor and a 36-1 wheel. Cam is two wire Ford "cam sensor". Will use Ford PWR idle valve. Bosch TPS. GM MAT and CLT. Bosch high Z injectors.

Thank you all for answering my post.
a) no "jumpers" came with megasquirt3 built. There were 40-50 little bags but I have not thrown anything out. No problem, will source some if needed
b) apparently my CAM sensor is a simple switch, so no pull-up resistor needed

I will need to revisit my Crank sensor on 1,2, 26 as it is a Hall sensor and will need a pullup

c) I am in New Zealand. I have contacted Jared in Tauranga. I was going to hire him tune my build. The motor is still in the machine shop. I had hoped that I could have gotten the project further along before needing to hire help.

[jsmcortina]

On the V3.0 mainboard you use short lengths of wires or the trimmed of legs from components as the jumper wires. There's nothing missing.

James

[dontz125]

Cam is two wire Ford "cam sensor".

b) apparently my CAM sensor is a simple switch, so no pull-up resistor needed

Your cam sensor is a VR sensor, NOT a 'simple switch', and must be fed through the cam VR conditioning circuit on the 3X card. As you say, no pull-up.

On the V3.0 mainboard you use short lengths of wires or the trimmed of legs from components as the jumper wires. There's nothing missing.

True, but JP3, JP6, and JP7 - the items under discussion - are on the MS3X Expansion Card, and do use jumper caps.