This is a very simple project indeed: add a line-in input feeding the amplifier in my sister’s CD/Tape/Radio, which has much better sound than the ‘device’ she mainly plays music from. How hard can it be to find the amplifier IC and feed in directly?

Taking the thing apart was none too hard, and it’s cheap ’90s hardware so all through-hole and single-sided PCB. I found the mode switch, traced it back to the amplifier, paid careful attention to the pinouts and soldered a small cable onto one input, the other end going to a 555 ‘signal generator’ kit I had lying around. Power up: the signal generator exploded and the lcd backlight died.

By this point we have all we need for a basic charge, and I do actually need to charge some batteries. I can build a simple current regulator with an LM317 and a resistor, which will be good enough for now.

No Termination

The simplest thing would be just to charge some batteries and log to the computer. There’s a marvellous thing out there called FeedGnuPlot which makes graphing realtime or static data so easy one has to resist the temptation to graph everything. But before we can do that, we need to be able to read analogue values and throw them over USB.

As part of the Battery Charger project I need a basic PIC dev board. I built one a long time ago for A2 coursework, and I even found the artwork lying around, but the tracks and pads were too small for hand etching and drilling. Trying to open the cad files in KiCad I discovered that they’ve changed everything, and half the symbols ‘cannot be found’. I’ve also completely forgotten how to use KiCad or schematic capture/Pcb design software in general: all pointing to a need to redraw.

There are lots of ‘smart’ chargers out there. Most of them boast that they can charge your batteries quicker than the competition, and that a ‘smart’ algorithm will somehow prevent packing as much current as possible into a cell in the shortest time from having deleterious effects. Slow chargers are harder to come by: there are the cheap constant-current things you run for a certain amount of time—but if your batteries are not absolutely dead they will overcharge, and probably overheat and explode, as mine did. So not ideal. A few vacations ago, as a break from reading, I converted an old analogue ammeter into a basic adjustable-current charger with current and voltage read-off. The current regulation is not particularly clever. It uses the ’trick’ I devised for my AS Electronics coursework

Embedded Linux is currently all the rage with little boards like the Pi running a full-fledged Debian just to flash a few LEDs. Now certainly, the Pi would find uses here, but it’s hardly cheap. What is cheap—or even free—is defunct wireless routers. They, too, are embedded systems running Linux. Unlike the Pi they have on-board wifi and an ethernet switch; the cpu isn’t usually too bad either. I also picked a few up for £0.99 on Ebay. Here’s one: