- Tue Aug 18, 2020 8:15 pm
#44795
Hi,
I am wiring in my 0.4.4 board to an MX5 VVT engine in an 1998 NB 1.6 car. I figured out most of the wiring but I have a question about the fuel relais and the cooling fan signal. Just to warn you; I am a mechanic, I have no clue about electronics.
I bought the ULN2803 IC and mounted it as per this suggestion: viewtopic.php?p=20974#p20974, so now I should have a tach signal on Speeduino output pin 18. So far, so good. To do this right, I soldered the pull up resistor to +12V and IC pin 13, not 14 as mentioned in the link, to react to pin 49 of the Mega and feed output pin 17 of the Speeduino board, as per the pins mentioned in this link: https://wiki.speeduino.com/en/boards/V04, 1/3 down the page. I assume this is correct, although I differ from the first link.
Now I need to also set-up the fuel pump relais and the cooling fan relais. My first guess would be to add two more pull up resistors (10k?) to pins 11 and 12 of the ULN chip and to 12V of course. So Mega pins 47 and 45 are hooked up to Speeduino output pins 15 and 16 in similar fashion as the tacho signal above.
But here's the problem I cannot wrap my head around: the fuel pump relais requires 12V, the relais already has a ground wire attached permanently. But the fan relais is wired the other way around, it has a permanent 12V attached permanently and the wiring going to the ECU should be grounded there to switch the relais. So either one of these relais is not powered correctly when set-up identically. I don't think inverting the Mega pin setting will change this (cannot really explain why I think so), I feel I need to change more, put the pull-something resistor somewhere else on the fan set-up. But I cannot seem to figure it out.
Please advise, as far as I am aware these are the only two issues left before I can connect everything and power up...
Cheers,
Hugo
I am wiring in my 0.4.4 board to an MX5 VVT engine in an 1998 NB 1.6 car. I figured out most of the wiring but I have a question about the fuel relais and the cooling fan signal. Just to warn you; I am a mechanic, I have no clue about electronics.
I bought the ULN2803 IC and mounted it as per this suggestion: viewtopic.php?p=20974#p20974, so now I should have a tach signal on Speeduino output pin 18. So far, so good. To do this right, I soldered the pull up resistor to +12V and IC pin 13, not 14 as mentioned in the link, to react to pin 49 of the Mega and feed output pin 17 of the Speeduino board, as per the pins mentioned in this link: https://wiki.speeduino.com/en/boards/V04, 1/3 down the page. I assume this is correct, although I differ from the first link.
Now I need to also set-up the fuel pump relais and the cooling fan relais. My first guess would be to add two more pull up resistors (10k?) to pins 11 and 12 of the ULN chip and to 12V of course. So Mega pins 47 and 45 are hooked up to Speeduino output pins 15 and 16 in similar fashion as the tacho signal above.
But here's the problem I cannot wrap my head around: the fuel pump relais requires 12V, the relais already has a ground wire attached permanently. But the fan relais is wired the other way around, it has a permanent 12V attached permanently and the wiring going to the ECU should be grounded there to switch the relais. So either one of these relais is not powered correctly when set-up identically. I don't think inverting the Mega pin setting will change this (cannot really explain why I think so), I feel I need to change more, put the pull-something resistor somewhere else on the fan set-up. But I cannot seem to figure it out.
Please advise, as far as I am aware these are the only two issues left before I can connect everything and power up...
Cheers,
Hugo
- By PSIG
- By AlainNotHere
- By pazi88