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5Vout capacity and LAN

Posted: Tue Apr 10, 2012 4:15 pm
by Jasper K
Hi there,

I'm in the middle of making a loom for the S8 for my car and would like to know what the actual 5Vout1 & 2 capacity is in terms of Amps. Is it current limited?
When doing a quick LAN wiring trial to make sure I was doing it the proper way I found something strange. I connected as follows:

RJ45 --------> S8

1 #85
2 #86
3 #87
6 #88

This worked fine but I have also tried the following:

RJ45 --------> S8

1 #87
2 #88
3 #85
6 #86

This also worked fine. How come the LAN connection works either way. That's a bit surprising. I hope somebody could shed a light on this. Thanks!



Re: 5Vout capacity and LAN

Posted: Tue Apr 10, 2012 10:38 pm
by TimH
Sounds like the S8 - or your PC - has "auto-crossover" detection. The two pairs are nominally TX and RX, so TX from one device should, in theory, have to connect to RX on the other device, and vice versa. It is quite common for devices to be able to work out that TX has been connected to TX, and "swap" the RX/TX connections. Very common on Ethernet switches etc.

Can't comment on the 5V current capability though.

Re: 5Vout capacity and LAN

Posted: Thu Apr 12, 2012 7:54 pm
by pavlo
Of course the 5v is current limited. It is there for sensor power supplies only and you are talking 50-100mA at a guess. If you start to pull the voltage down then ratio metric sensors like a 5v map sensor will start to give proportionally lower outputs. If you need to power something that is going to pull a bit of current, like a small micro controller that is providing high level outputs, then you should really provide it with a 5v regulated supply fed from vbatt.

The LAN should be connected so the RX pair on the S8 are wired to the conventional TX pair on the plug and vica-versa. It is more likely that it is your laptop that autonegotiated which is the spec for gigabit lan, but not 100base TX so you want to work on the lowest common denominator just in case you use a laptop that has a port that doesn't auto neg properly.

Basically, you should always aim to do everything properly rather than to take shortcuts because it might be slightly easier. It only takes one "bad" shortcut to cost you a hell of a lot of time.