I was originally tasked with developing the hardware and software for a cash handling machine. This particular one was kind of like an ATM on steroids. The first two sets of pics are from that machine.

Cassette Controller
The cash in the machine was going to be contained in pre-loaded cassettes… this controller was the brain behind a cassette.

 

General Purpose IO Board
As well as our own hardware, we needed to talk to a variety of other bits and pieces, like coin and note validators. This board was designed to handle that kind of job. The solder pads on the lower half allow the configuration of the inputs (Pulled High/Low, Debounced/Straight Through) and the interrupts (the 4 interrupt lines of the PIC could be connected to anyone of 8 inputs either as is or inverted). The board also had plenty of scope for memory (maximum of 3 x 32K FRAM on the SPI bus).

Dance Floor
This is inspired by the First East Disco Dance Floor, and was intended as a commercial product. The final control board design has an ethernet enabled PIC on it, so we could in theory have a dance floor that was 256×256 cells (IP addressing and network bandwidth allowing). This prototype had an RS-232 link to a PC and some real basic software, but the hardware worked a treat. The LED matrix is 8×8, each cell has a red, green and blue LED… thats a total of 200 wires connecting the matrix to the controllers (and I had to crimp each one ).

 

 

On a more serious note though, I have facilities to handle small scale prototyping and firmware development for a large number of PIC microcontrollers, so if you have a requirement for some custom digital electronics or a custom PIC based controller, please feel free to drop me a mail to discuss your requirements.

If you are tech savvy and know what an electrolytic capacitor is and what it does when used for power supply smoothing, you can skip this next section.

For those of you who don’t know what an electrolytic capacitor, here’s a quick run through.

Capacitors are electronic components that store electrical charge. Electrolytic capacitors are a special variaety, most are made out of aluminium foil, paper and a substance called ‘the electrolyte’. This is all wrapped up and sealed in a small aluminium can. These capacitors are mostly used for smoothing power supplies. The general idea is that you connect one across your power supply lines. It charges up to the voltage present on the lines, then if the voltage dips mometarily, the charge from the capacitor will supplement the power and help smooth out the bump. That in a paragraph is what these components are and what they do… in one case.

The problem with them is that they are quite volatile. The electrolyte is normally an unpleasant concoction of chemicals designed (I think) to help store the largest possible charge in the smallest possible area. The particular problem this post refers to is caused by bad electrolyte. By bad I mean it degrades easily, and when it does, the capacitors can fail. When they fail, they can explode and spew their content all over the inside of the equipment they are in. A prelude to this is sometimes bulging of the can of the capacitor and/or leaking electrolyte.

In bad cases, the electrolyte can breakdown completely, when this happens a short circuit can develop and this will ultimately result in big problems.

So far in the last 18 months or so I have had to repair three items of kit… all failed because of faulty capacitors. The first was our DVD player. It started suffering problems… tray wouldn’t open, when it did, it wouldn’t close… it had intermittent crashes at various points. These problems got worse until it finally gave up the ghost. A quick peek inside and it became obvious what the problem was. An electrolytic cap on the power supply board was bulging. Whipped it off the board, stuck in a new replacement, fired it up… perfect. The second item of kit was a little trickier to deal with as it is significantly more complex and a hell of a lot more expensive to replace.

Spirit’s computer. EEP It just stopped. After having numerous problems with it, that gradually got worse (these problems included random crashes, weird BSOD’s, graphics cards appearing to fail, lots of memory access errors and numerous others), it finally got the point where it wouldn’t even run past the BIOS POST. And towards the end of 2005, my development database server had become so unstable it was unuseable. This particular machine had been getting worse and worse over about 2 years… it started with simple hang ups when running X but progressed to the point where the only way it would survive the day was if it was fired up and left well alone. These two machines are now running sweet after I risked it and replaced all the electrolytic caps on the motherboards myself.

Anyhow, the point is, if you are experiencing weird problems you just can’t explain or get rid of, then this could be the cause. You can, if you feel up to it handle the recapping of a motherboard yourself, but its not a nice job. It took me over 6 hours to recap Spirit’s motherboard and about the same plus numerous trips to the local RS trade counter to fix up mine. But it was worth it. The graphics card we thought was failing appears to be working perfectly. The machines seems to be running better (can’t explain this) and so far they’ve been used pretty heavily without any problems (touch wood).

My one piece of advice, which is covered on badcaps.net (a site dedicated to the problems of numerous motherboards which have failed due to faulty caps) is always use the correct size of capacitors. This applies to the capacitance value (this is measured in Farads, although a Farad is rather a large unit, so most electrolytic caps use micro-farads (uF) to measure their capacitance). The rating (this is measured in Volts. The rating of a replacement must be equivalent or greater than the rating of the existing part). And last but by no means least, the physical dimensions. Because I needed to get the machines up and running in a hurry, I took a couple of gambles. I didn’t check the length. Most caps used on motherboards are radial devices (that is the two connection leads protrude from one end, allowing the device to stand vertically), since they have a height above the board surface, if they are too long they can get in the way of heatsinks and expansion cards. So, if in doubt, double check what you can get away with by measuring it up. The other critical dimension is the diameter. If the devices are sitting right next to each other on the board, if they are too big, you won’t be able to replace them.

Thats all I have to say, apart from thanks to badcaps.net for the excellent information.