USB driven battery pack for Pentax 67

Last year I finally got off my duff and made a useful mod for my astrophotography.

Since the Pentax 67 and 6x7 uses the battery to operate the shutter, there has long been an accessory for an external battery for the camera.  It allows the battery to be removed and put into a warm pocket or plugged into a larger battery pack.

A nice trick about most of these bodies is that once a bulb exposure has started, you can remove the battery and the shutter will stay open until released.  Thus, most of these devices have a headphone  plug that facilitates this disconnect.

Over the years, I've have enough of the hassle of keeping track of the batteries and the external battery pack.  Many times I forgot to shift the battery pack when winding film or I'd shorted out the pack and discharged it.  Staying awake all night didn't help with keeping track of these little things.  I figured, if USB is providing 5V already, why don't I just give these cameras juice off the USB hub?

I sacrificed a few dead (computer) mice to get their USB connectors, then soldered their cables to some headphone jacks to use the above disconnect feature.  I did use a multimeter to identify which wire provided the +5V vs ground since the USB has several data wires vs just voltage.  That's the only step that required special effort.  I didn't want to put any smart devices at risk, so I just used an accessory charger to confirm which wires were the important ones to use.  This test eliminated any voltage across the data lines, so I didn't have to worry about unintended connections causing data problems for other devices on the same hub.

Once connected, the cables now reach from the cameras all the way to the ground, allowing them to be put into the same bundle that the telescope uses.  The power requirements are miniscule compared to the drain of using an active USB hub.

Now I have been able to run 2 cameras indefinitely on Bulb for astro work.  No more issues of remembering to keep batteries around or fiddle with connecting or disconnecting them.

The reason why I bring the topic up is because I recently managed to mangle one of these external battery packs.  I let it get snagged on the mount and it was rent by an unattended slew.  Since I recently repaired one USB thing, I guess I'm on a roll and it's time to fix another...