2022.11.11: Lux Turpis ("Light Mixer")

2022-11-11 21:44 by Ian

Lux Turpis is an ISM radio relay and NTP appliance.

Hardware at various stages of assembly

I bought a few obsolete AeroHive outdoor WiFi APs at a scrap rate from Unix Surplus, The guts were mostly useless, but I got the two cast aluminum enclosures with full mounting kits for $25/ea. I think these must have cost AeroHive at least $150/ea to produce. They're well sealed against weather and RF, and it was perfect home for a freak-of-engineering.

I cut up some Al 6061 sheet to act as a mounting platform for custom parts, and milled out the unused elements of the casing's internal design.

Additional cuts had to be made to allow the PCB to sit low and allow for clearance for the radio modules on wires without risking it being crushed when the casing is bolted closed.

Here is that plate after standoffs were mounted and ground flush. The main PCB is mounted in place.

Test-mounting of the Raspi... Clearance was perfect. Nothing else of interest is mounted on the bottom aspect of the plate. Difficult to see in this photo is a ribbon cable to the GPIO header of the Raspi.

Mounting plate completed with the addition of the PoE adapter(2A @12V) and the DC-DC converter (module rated for at least 6A @5V). All heat producing elements are thermally bonded to the plate (or casing). Components were chosen such that linear regulation would be used only at the last-step of conversion (if at all). PoE gear tends to run rather hot when draw increases. So the less voltage reduction that needs to be done there, the less it should burn off as heat. The finished hardware doesn't consume more than ~5W at peak, but since it is an outdoor machine that might be in direct sunlight, it needed to be somewhat overbuilt to remain in constant reliable service.

The lightning arrestor PCB and mountings were retained.

This is the final state of assembly before the lid is screwed on, and the whole box mounted alongside the antenna mast.

The mounting brackets for the antenna mast are installed and grounded.