Archive for April 4th, 2012

KG-UV3D GPS+Voice Interface: Battery Case Latch

The Wouxun KG-UV3D radio has two lugs inside the battery compartment:

Wouxun KG-UV3D - battery lugs

Wouxun KG-UV3D - battery lugs

The battery packs and DC adapters all have clever spring-steel latches that engage those lugs, with a pair of sliding buttons that depress the ends of the spring to release the pack:

Wouxun KG-UV3D - battery pack latch

Wouxun KG-UV3D - battery pack latch

That mechanism may be cheap, straightforward, and easy to build in mass production, but I can’t figure out how to duplicate it for a case to house the GPS+Voice interface circuitry. That box had the dual disadvantages of being plug-ugly and not locking to the radio, but it did help establish some key dimensions, which is not to be sniffed at.

A bit of heads-down effort produced this not-so-hideous printable case:

HT-GPS Adapter Case - Overview

HT-GPS Adapter Case - Overview

The rectangle on the top is a built-in support structure for what will be a window over the four LEDs on the Byonics TinyTrak3+ board. The two holes on the top allow screwdriver access to the TT3 trimpots, although they might not be necessary. The four holes (two visible) along the sides fit 4-40 setscrews that lock the PCBs into slots along the inside of the main case body. The red doodad off to the far side is that plug alignment block for the radio.

The yellow latch plate on the end engages the lugs with a bar sliding in a slot, which looks like this when it’s locked:

HT-GPS Case Latch - locked

HT-GPS Case Latch - locked

A view from the top side shows the notches that release the lugs:

HT-GPS Case Latch - detail

HT-GPS Case Latch - detail

In the unlocked position the notches and lug slots line up:

HT-GPS Case Latch - open

HT-GPS Case Latch - open

The solid model shows the plastic structure, which is slightly improved from the pictures:

HT-GPS Case - latch and connector plate

HT-GPS Case - latch and connector plate

The big hole fits around the TinyTrak3+ serial connector to the GPS receiver. The slot across the hole splits the plate so it can fit around the already-soldered connector.

The latch bar consists of a L-shaped brass angle (from the Big Bag o’ Cutoffs) with two snippets of square brass tube soldered to the ends:

HT-GPS Case Latch - bar detail

HT-GPS Case Latch - bar detail

I cut the angle to length with a Dremel abrasive wheel, soldered two brass tubes, sliced them off with a Dremel cutoff saw, roughed out the slots with the abrasive wheel, and applied some tool-and-die maker’s (aka needle) files to smooth things out. Yup, had to clamp each soldered joint in a toolmaker’s vise to keep from melting it during the nastier parts of that process. A pair of 2-56 screws, with nuts behind the plate, hold the bar in place and provide some friction.

Moving the latch bar requires poking the end with a sharp object (captured by the brass tubing), because I couldn’t figure out how to put finger-friendly buttons on it. This would be completely unusable for an actual battery, but should work OK for a permanently mounted GPS interface.

Conspicuous by their absence:

  • Holes in the case for the cables (may need more surface area on the ends)
  • Any way to fasten the latch plate to the main case (I may just drill holes for small pins)
  • Provision for the TT3 mode switch
  • A cover for the exposed radio chassis above the latch lugs (may be a separate shell glued to the latch plate)

The whole thing needs a full-up test to verify the serial connector clears the back of the case…

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