battery-operatedcasesmount
I'm trying to mount AA terminal contacts in an anodised aluminium case. Given that the aluminium is anodised, does that mean it's not conductive and the contacts could directly make contact with it? If not, what's a good way to mount contacts on an anodised aluminium case?
Thanks
For extruded aluminum, find the local distributor for aluminum structural framing in your area. Try 8020.net in the US and Bosch-Rexroth in Europe. You might also try frontpanelexpress.com, though their stuff might be too big.
Here are some options to mount the PCB:
For the PEM studs, check out the KSSB family-- they're designed specially for mounting PCBs without extra fasteners.
The CP2102 USB to UART Bridge has an unbalanced 3.3V interface so you should be connecting ground in addition to the TX and RX lines. Using a shielded cable probably isn't a bad idea although at fairly standard low baud rates such as 9600, 57600 etc noise immunity is fairly good so you may not have to worry a lot unless the application is critical or you're in an electrically noisy environment. For test purposes I've run 3.3V TTL serial lines over a few meters of unshielded cable without problems.
A connector I've used in the past that is quite robust and offers panel mount in a small form factor is the Binder 709/719 series. The 3-way panel mount part number can be found at Element 14: Binder 09 9750 30 03. They are a little larger than your specifications and not exactly dirt cheap but are very easy to solder to, here's an indicative photo that shows the 4-pin variety:
Your idea of using a 2.5mm audio jack is probably also worth considering although you need to be aware that while inserting the plug some pins can be temporarily shorted. The RX line being shorted to ground or TX won't matter but you should take care with the TX line at each end. Without specific details of the hardware at each end it's hard to know for sure but a 3k3 resistor in series with the TX line at each end will limit the current to 1mA which should be safe for most devices I can think of.
Best Answer
Coat the insides with scratch resistant isolation or fix the contacts such that they cannot touch the metal. Best option.
Anodisation in aluminium needs to be sealed to be reliable enough for real electric isolation. The anodisation layer can be punctured by sharp edges or worse: The chemicals inside a battery! Some electrolytes have a high or low enough pH or contain sufficient reactive Ions to take away the oxide layer, forming in some cases actually conducting wet-mass for a while. Since I assume you have no crystal ball to see if the batteries will ever leak, it's a decent risk. Anodisation may help retain the coating (due to surface roughness and/or porousness) and/or reduce the layer thickness requirement, depending on the chemical process used.
Many cheap-ish polymer coatings can handle these chemicals and light mechanical pressure, epoxy coatings would be good to a degree I'd expect. (<-- I'd expect... certainties come from spec- and/or datasheets.)
Of course in caps and such the anodisation works, because it's a thoroughly conditioned environment and the anodisation is done under very strictly controlled circumstances until all has been sealed in oil or plastic to prevent thermal cracking or mechanical damage. This is also one of many reasons a cap should not dry out. Dry cap != protected any more.