I did some more testing of the battery options for my phone backlight. I tried the Lithium Manganese 3V pouch cell to power the boost converter, which could supply the LEDs with 24mA at 12V and was incredibly bright. However, the current decreases pretty rapidly as the boost converter is draining the battery hard to provide that current. so it won't last very long. Unlike conventional batteries the cell voltage does not bounce back up after the load is disconnected either.
I then tried the other idea of 2 CR2032 coil cells in series to give 6V. As this is closer tot he output voltage of the boost converter it doesn't need to pull quite as much current from the batteries. it was supplying about 19-20mA to the LEDs, which decays the longer it's left on but bounces back a bit after being turned off for a while, so they should last a bit longer. Here's a pic of how brighti t looks with a pair of pretty well used coin cells (this was taken under strong LED lighting and with flash on the camera):
That's the ID image that was posted for free on here a while ago laser printed onto a transparency. Is it Birdie who can supply a file of the more accurate image?
As coin cells were the way to go, I had to think about where I was going to put them (and make it easy to change them). The wallet I've got doesn't have much room in the ID pocket - I can just about get the backlight panel into it. I could either unpick the stitching and insert another layer to make more room in the pocket to put the cells behind the backlight, or look at moving them over to the badge side (which has a very thick piece of leather around the badge). This would mean routing some cutouts in the back of the badge to accommodate the cells and the boost converter, so I set to it today. I drilled about 120 1.5mm holes 3.5mm deep (which was about how much I reckoned I could get away with without breaking though) by hnnd with a pin vise, and then used the milling bits on my rotary tool to rout out the rest of the material and tidy up.
The cells will have copper or brass strips underneath them for the +ve and -ve terminals, and a sprung copper or brass bar screwed across them to connect them together and hold rhem in. I did break through in one area (where II lost concentration and put a little too much pressure on the pin vise) which left a small hole in the bottom of one of the 'valleys' above the LAPD logo. I managed to fill it with a little putty and touch the paint and weathering up though.
Now i'm just waiting for my reed switch to come before I get it together.
