help with creating a tach output

[falcon fanatic]

Hi,
First let me say that I'm pretty new at electronics so things that may seem obvious to some won't be to me. I have a pre-assembled MS2 v3.57 up and running, but I need a tach output. I have 5 free wires left on my DB37 harness, they are SPR1 through 4 and also the one marked PWM IDLE. I also have six possible outputs on my DB9 connector. Questions:

1. Can I use any of the existing DB37 wires to drive a tach?
2. How?

I'm looking at the Tacho output page in the manual (page 40, section 3.5.5 This page: http://www.msextra.com/doc/pdf/html/MS2 ... .4-40.html ) and I just don't get it. Can someone direct me to a tutorial?

OR, can I trigger it off one of my coils from my wasted spark system? That'd be the easiest.

[nismoautoxr]

What kindof tachometer? You can use a number of outputs such as FIDLE but you need to know what kindof tach you will run . If its a tach commonly run from the negative side of a distributor system coil then you will usually need to build a high voltage type circuit such as the relay field type in that link you posted. I had to build that same circuit for a Toyota I did a few years ago . Not the simplest thing in the world but the instructions are right there..

You also have several pads on the 3.57 board that can have jumpers soldered from to SPR1 through 4 that can also be outputs for your tach as well but you will still need to make sure u build the appropriate circuit for the type tach you wish to use. You will not be able to hook a tach to 1 of your wasted spark coils to do it though.

[falcon fanatic]

Right now I'm using a cheapo Sunpro tach. Had it connected to the negative terminal of my coil before as per linked instructions. Would anyone be able to tell me whether this will require a relay coil to trigger?

http://static.summitracing.com/global/i ... nglish.pdf



Also, on these diagrams I see reference to (S12) as a 12v source. Is that JS12 on the board?

[nismoautoxr]

Yes I'm pretty certain you will need to build the relay coil circuit for that tach in the link you posted. FIrst lets answer some questions. Did you run the jumpers http://www.msextra.com/doc/pdf/html/MS3 ... e-1.4.html

If you did then you already have at least 2 wires already you can hook up as you tach output. You can use either IAC1 or IAC2 provided you have not already used those. Those can be used directly without any further work. If you have used them then you will need to build thecircuit in the link you originalyy posted and pick an appropriate processor pin such as JS10,JS11,D14,D15,D16 etc. It all depends on your build choices so far.

You can also build that relay coil circuit outside the Megasquirt using the Fidle wire as the input to the circuit. That's how I did it on the Toyota . I built it in the harness.The options are pretty numerous. Pick one.

[slow_hemi6]

Nothing wrong with a sun tach in an old car. Nothing looks worse than a boy racer tach in a classic. My SunPro had a selector for 2,4,6,8 and being v8 wasted spark I could run it from 1 coil and set at 2. A bit grainy at idle revs (slight needle twitch) but otherwise fine. No good for you with a 6cyl though. The pdf you linked to said that the tach can work with a DIS system so I would probably try the non relay coil drive circuit first. Then if no luck try the relay coil one.

[falcon fanatic]

Okay, sounds like I'll try the easy way first, and if not then I'll build the relay coil. Do I do all the work on version 1 internally or externally?

Here is a nice thread on a relay coil build, any opinions on this approach? Seems sanitary: http://www.msextra.com/forums/viewtopic ... er#p457530


Also, nismoautoxr, the link you shared showing the suggested jumpering links to the the cover page of the manual. What page where you going for? I think I'll use fidle to run my fan and then SPR 3 or 4 for the tach. All four IAC outputs are occupied operating a stepper motor.

Thanks for all the suggestions. Still learning to read the electronics diagrams, but also sometimes it is unclear whether things should be done inside the MS box or externally. Also, where do folks go for transistors and other components? My local Radio Shack ain't what it used to be... more of a Radio Snack these days.

[DaveEFI]

In the UK, the large electronics suppliers like CPC and RS are now doing free next day delivery and no minimum charge for credit card online sales. Very different from a few years ago. So check the deals from Mouser and Digikey, etc. But they may not sell you one cheap transistor - may be a packet of 5 or whatever. Good way to build up a stock.

Ebay can be quite useful too. But you do need to know what a particular transistor etc costs from the big boys to avoid being ripped off.

[nismoautoxr]

sorry I meant for it to be this http://www.msextra.com/doc/pdf/html/MS3 ... 1.4189.png

but since I read that you used a jeep throttle body you are probably using a stepper IAC so that is moot

[falcon fanatic]

but since I read that you used a jeep throttle body you are probably using a stepper IAC so that is moot

True, but seeing how those jumpers are installed helps me visualize and understand the process better. Keep in mind that I ordered my ECU pre-assembled so I haven't actually done any work directly on it yet. Every piece of piecing this knowledge together helps me build the confidence to start altering a multi-hundred dollar board.

[nismoautoxr]

I quite honestly build these things because I enjoy the trip almost as much the destination . I always buy the 3.0 boards because I learn alot from tinkering around with it. The 3.57 board doesnt let me do that. I've never dealt with a.3.57 board but I've heard that it is not very repairable so do be careful as it looks like you are. This stuff is pretty robust and forgiving to mistakes so some trial and error is ok as long as you don't do anything too crazy. It's only money right