Tachometer output pin - why no Led18?

[Keithg]

Well, I am about to go to wheel decoder with wasted spark and want to retain my tachometer. It appears that the 'tach output' is what I want to enable. When I go there in MT to select the output, I noticed that led18 is not an option. I am not using led19 (led 17 and 19 are spark A and B). Is there a reason for this? I ask because led18 already has a drive transistor and I would not have to fashion an output board. I will peer through the code and see if I may be able to do this myself, but thought I'd post here to see if I am just not making any sense.

KeithG

[Keithg]

here I go responding to my own post again. I thought about it, and
just connected the led18 circuit (drive transistor and led) to output
x2. Unsoldered the right hand side of the resistor and stretched it to
the X2 pad which is near by. Piece of cake, actually. It works
beautifully.

Thanks for all the hard work!

KeithG
Posted by email.

[jsmcortina]

Funnily enough, LED18 can already be a tach output, set it to "IRQ trigger" and it does the same thing, but no divider option.

I didn't add LED18 as an option because LED18 is sparkC so it seemed not much use for 6+ cylinder engines.

James

[Keithg]

well, I was not thinking here... maybe this little note should be
added to the 'tacho out pin' information for those of us that have a
tach matched to the number of cylinders and do not need to divide,
though my little 'mod' was pretty simple...

KeithG
Posted by email.

[fritoss007]

Question from a newbie !!!

how do i know the positive from the negative on the led 18 ???

cause i need the use the - to drive my stock tacho ??

thanks alot guys

[jsmcortina]

The "-" is the one with a "-" beside it on the circuit board

James

[fritoss007]

should i directly hookup the tach signal wire to the "-" of the LED18 ??

these leds are not 5Volt ???

cause i set IRQ trigger to LED18....and no more RPM !!!

my tach is OK....cause when i use the "-" on one of my coils i got half of the RPM !!!