Computing stuff tied to the physical world

Plug pinout

In Hardware on Jul 8, 2009 at 00:01

Here is the standard pinout I will be using for all my JeePlugs and port connections from now on:

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Do not ask how many different variations and scenarios I’ve been through. You don’t want to know. I’ve got the scars and JeeNode debris lying around here to prove it. I agonize over these choices so you won’t have to …

There are difficult trade-offs whichever way you go, but this is it. The best choice, period.

From that, several consequences follow. The most important two being that the JeeNode v3 and the JeeLink will be supplied with female headers for the ports, and that these headers should be soldered on pointing up.

If you have the v2 JeeNode, then my advice is to make a couple of conversion cables or plugs, so that you can set up all future connections using new standard. That’s what I did anyway – I don’t even have a v3 JeeNode here yet, and I’m already wiring up new plugs using the above convention. The pain of converting now is nothing compared to having a confusing mix of boards and plugs and cables later.

Depending on the power source you use, plugging in things the wrong way can definitely damage circuits. I suspect that a 5V power source such as the fused one from USB on the JeeLink is relatively safe, but a 12V PWR line hooked up the wrong way is likely to damage the ATmega. So will shorting pins 1 and 2, i.e. PWR and DIO.

If you need to work with such “high” voltages, I would suggest using 4-pin plugs where possible. In other words, don’t even bring that PWR line out to the peripherals / plugs unless needed.

Back to the pinout and orientation of plugs. With female headers on the JeeNode / JeeLink, you can see that plugs will be oriented with the components sticking out.

For plugs requiring two ports, you can mount the male headers pointing down on the JeePlugs and use them as tiny shields. Plugging such a shield in the wrong way, i.e . turned 180°, has no serious consequences. The ports 1 & 4 or 2 & 3 will simply be exchanged. Your sketch won’t work, but at least it won’t cause any electrical shorts or power-line mixups. Plugs used as tiny shields are quite robust in that sense.

That’s it for using plugs (or your own perf-board) and hooking up stuff to each port. By sticking to these conventions, it will be easy to re-use components in different configurations later.

The choice for non-polarized pin headers was a very deliberate one. They are very low cost, small, and widely available. This matters to me because I intend to hook up tons of different things over time. It just means we have to carefully pick some conventions and stick to them. Done.

Tomorrow I’ll describe another variant compatible with this which helps avoid inadvertent reversed connections and which supports chaining with a port as I2C bus. It will also make it easy to construct a more permanent mechanical “fixture” when hooking up multiple sensors, indicators, actuators, etc.