MoTeC Global Forum

Hi,

I'm setting up a shift light using 4 Aux outputs which will drive 4 pairs of leds.

Aux1 will turn on at 4000rpm, aux2 at 6000, aux3 at 9000 and aux4 at 12000.

LEDs are permanently connected to ground and I was expecting the auxiliary outputs to bias them with 12v. Each led has a resistor (they're 4V leds).

My problem comes when I see that the only output that will send 12v to the LEDs is only Aux1. The other outputs will only send 2-3V. Reading the manual, I see that the only trouble could be the power consumption, but assuming that every led will consume just about 50mA, I don't think this is the problem.

Am I missing something? I just thought that all the outputs would work like aux1.

Thank you very much. Regards.

Nearly always it is best to use lowside mode. That means you supply live 12V from the ignition switch/relay to one side of the LEDs and the ECU switches the ground on the other side.
According to the help file only Aux 1,2,5,6,7,8 are capable of doing it in high side mode like you are trying to do so if you want to keep it that way then change the 3 & 4 LED's to one of the Aux's listed above.

AdamW wrote:Nearly always it is best to use lowside mode. That means you supply live 12V from the ignition switch/relay to one side of the LEDs and the ECU switches the ground on the other side.
According to the help file only Aux 1,2,5,6,7,8 are capable of doing it in high side mode like you are trying to do so if you want to keep it that way then change the 3 & 4 LED's to one of the Aux's listed above.

Thank you for your fast reply.

I understand what you mean, but let me throw you now another question:

The ECU is now capable of sending just 2-3V, so If I do what you suggested, the leds will have a permanent 12v on one side and ground on the ECU side when I reach the desired RPMs. But until I reach those RPM it will actually send 2-3V (just like it's doing now), suplying the leds with 9-10V. Won't this make the leds never switch off?

And I forgot to tell that I'm using Aux1, Aux3, Aux4 and Aux5. If Aux3 and Aux4 can't handle a high side output I'm doing this wrong, but Aux5 should be capable and it won't work on high side

spyro512 wrote:I understand what you mean, but let me throw you now another question:

The ECU is now capable of sending just 2-3V, so If I do what you suggested, the leds will have a permanent 12v on one side and ground on the ECU side when I reach the desired RPMs. But until I reach those RPM it will actually send 2-3V (just like it's doing now), suplying the leds with 9-10V. Won't this make the leds never switch off?

I dont think I've ever used an aux to drive a LED with a M*00so cant say with great confidence, but I suspect the 2-3v that you are seeing is just the output in floating condition. A DVM will pick up a trace voltage but there will not be enough current to drive anything.

spyro512 wrote:And I forgot to tell that I'm using Aux1, Aux3, Aux4 and Aux5. If Aux3 and Aux4 can't handle a high side output I'm doing this wrong, but Aux5 should be capable and it won't work on high side

There are still a few errors in the M84 software/documentation so it could be that none of them can do high side mode. It should only take you a few minutes to rig up a jumper wire to try it in Low side mode so I suggest you give it a try...

It worked perfectly on low side thank you very much!

If you aren't using 5v Aux or 8v Aux for any sensors you could use that as a lower voltage power source for up to 150mA or so. But double check and make sure you won't exceed the current capabilities, they aren't all the same.