Strobe Quench Controller Power Supply - Part 2
My current challenge was to provide a suitable power supply for my 5 volt Arduino Pro Mini that I was jamming inside a reclaimed SEA & SEA TTL converter. The converter previously used a CR-2 battery which would not provide enough voltage for my Ardunio.
First thing that came to mind was a stack of button batteries. Which ones would fit? How many did I need? This was when I learned that the cryptic numbers associated with a button battery mostly made sense. The numbers normally indicate the physical size of the battery. A CR14250 is physically 14.5mm diameter x 24mm thickness.
I had a 15.6mm x 27mm battery compartment available. My search now focused on any battery smaller than 15.6mm diameter. In the end I determined that a stack of 5 LR44 batteries (also known as AG13 in my local Dollar store, 10 batteries for a Dollar) would physically fit and provide enough voltage. The LR44 comes in several flavours (Silver Oxide or Akaline) with many different designations but physically are 11.6mm x 5.4mm. The stack of 5 was the perfect length and pushed put 7.5 volts. This stack was small enough to fit (well, their smaller diameter meant that they rattled around a lot and became a jumble and not a stack) and provided sufficient voltage to power the Arduino.
So how best to make a stack of 5 LR44's that would fit properly in the TTL converter battery compartment?
The simplest solution would be to place a sleeve around the stack to fill the extra space. In a previous life I had tried to make a button stack battery by wrapping them in black electrical tape and / or heat shrink tubing. Results where poor. The challenge was to ensure that the batteries maintained contact with each other. By luck I discovered the perfect sleeve while wandering around a local surplus store: a bright red plastic 1/4 inch Phone Connector jack. A LR44 battery perfectly fit the internal dimension of the sleeve of the phone jack. And the sleeve slid into the battery compartment with about 1mm diameter free play. All I need to do was cut the sleeve to the required length.
The sleeve cut to length with 5 LR44 batteries inserted into it provided a suitable Arduino power supply. Lots of volts, maybe enough current? (see next post?) The only problem was it did not work in the battery compartment. I was missing a "button top". The CR-2 is a button top style battery (like AA's) that features a smaller diameter bump protruding as the positive terminal. My LR44s where flat top. The "top" of the battery stack did not touch the internal positive terminal of the battery compartment.
I needed a simple solution to either add a button top to every battery stack or alter the battery compartment to remove the need for the button. A battery side solution did not seem scalable as I expected I would need to use multiple batteriy swaps during a week of diving. Something on the compartment side seemed best.
During a search of my random parts drawers I found an aluminum spacer. It was a little too long, but with a little filing I shortened it to become a compartment side "button".
My home brew Quench controller powered up just fine. Nest step was a trial by sea! (well a 1 week trip to the Turks & Caicos)...