small update to MSS isntall guide

[mobythevan]

When I was fixing the last bug with my cranking timing I had also changed the pullup resistor on the trigger input to MSS to be a 1K resistor. I forgot about this until today when I was reading about an install on zcar.com, so I fixed the install guide schematics to reflect this. It is a good idea to use the 1K pullup instead of the 2K I had listed in the schematic before. The reason is because during cranking the voltage drops and the trigger pulse may not be as clean. That is it, BTW everything is still working good. The install guide is up to date now and Tony D. is working on using the 81 CAS with MSS. When he gets that to work I will add the specific info into the install guide.

 

I also added a few sentences to explain that I use the trigger circuit just like the assemble guide tells you to build it for use with the stimulator board. If you have assembled MS then you know what I mean. The install guide says to short out diode D8 and the jumper XG1 to XG2. I realized this could be an area of confusion for some people, so I wanted to clear that up.

[Jersey]

Thanks moby.

[Guest Boyd]

Moby, can you give me a short description of what a pullup/pulldown resistor really is and how I would wire it in to my 7pin HEI? I need 3-5 volts on the bypass line and it says to use a pullup resistor. Does this mean I connect the bypass to 12 volts with a pullup resistor (size?) inline?

 

I have looked around the web, but no luck understanding what a pullup/pulldown resistor and how to use it.

[mobythevan]

You use a pullup resistor to get your line(or pin,connection) to some voltage (5,12, etc). Suppose you want a pin to have 5volts. If you just add a wire to 5 volts there is nothing to limit the current and if the pin is say an input to a transistor that is switched to ground then you have a short to ground from 5 volts and you burn stuff up. So instead you add a resistor to the 5 volts and the resistor will limit the current according to ohms law. Current is voltage divided by resistance. If you put a 1k ohm resistor to 5 volts then if the pin is switch to ground by internal electronics it can only draw 5 milliamps max(the resistor current limits the path).

 

A pulldown is similar except that you want a pin/wire connected to ground and you want the path to be current limited.

 

To size the pullup or pulldown correctly you should know what the circuit is that you are adding the resistor to. But as a general rule you can use a 1k resistor for 5volts and a 2k resistor for 12volts. That limits the current to a few milliamps which is conservative. Sometimes the circuit may require more current to operate properly.

 

I hope this doesn't confuse you too much, I take electronics for granted so I make a lot of assumptions when trying to explain things. Ask more questions and sooner or later I will explain it right.

[Tony D]

so that's how it works, and what it does.

Thanks, from me, also. now I seewhat I am doing.

Wiring the engine bay this weekend. Dropped the engine in last weekend, but due to jobs out of the area, am not able to peck away at it for an hour or two each night like I have been doing for the past few months.

So soon I will post the results. I feel confident it will work the same as the late models, but this will dot the I's and cross the T's...

Again, thanks for the theory, I followed it.

[mobythevan]

Sounds like it is going good Tony, I am curious to see what you think when everything is working.

[midnightzxt]

I'm not sure how relevant this is, but what wattage should the pullup resistors be?

[Tony D]

I used 1/4 watt, since the 1/2 watt units looked damn big to me to fit and look decent on my relay board!

I have not had a problem using them at that level, they do not get hot in the least bit, and after several hours of test running I could see no change in the waveforms on the O-Scope.

Anyone else using anything BIGGER than 1/4 watt for the pullup's?

[Xander]

12 volts over a 1 k resistance will be only about 12 mA. 12 mA @ 12 volts is 144 mW. So 250 mW (1/4 watt) is fine for the resistor.

 

A typical hall switch can sink 100mA. So there is no problem there.

 

I think It's amazing how much you learn by building your own megasquirt.

 

Zya

[midnightzxt]

yeah.. i mean i TOOK electronics (basic) in physics.. but my book's at my house in chicago, while I'm at Purdue.. and I figured I could get a quicker answer by just asking.

[mobythevan]

Earth Is Round

 

heh heh

 

E

I R

 

E=I*R

I=E/R

R=E/I

 

I don't have one for power??

 

P(watts)=IE

P=(E^2)/R

P=(I^2)*R

 

To lower confusion I just use E everywhere for voltage, or to raise confusion????

 

Those are the only equations I ever use. I slept through AC circuit class in college. The prof was monotone. My friend said he would just walk up to my desk and look at me while I was sleeping and then go on. He should have kicked me or something.

 

I enjoyed op amp design the most. I ended up taking 3 different op amp classes while I was in school. I am sure I will end up with an op amp circuit hanging off my MSnS soon. I wanted to by some load sensors and build my own vehicle weight input, for using the g-tech stuff. Would be kind of neat to read out the weight real time on the laptop through MSnS. Might put off some women that get in for a ride.

 

Since this thread resurfaced can we move it over to the megasquirt area?