A friend gave me a Denon DHT-T100 to look at.
Do not spend much time on it.. ok.
It had a problem, it started clicking and ticking after power on, and after some time.
(a so called intermittent problem)
Sometimes it did not tick or click, but it was basically not usable.
The clicking had a sharp click in one channel and repeated after about a second, then sound recovered and it would click and drop out again.
He told me, do not spend any time on it, yeah, right. ;-) like I would give up after 15 minutes.
I wanted to know what was going on with this thing, I found some schematic online and started measuring the usual things.
The power supply, 24V did it drop down when a tick occurred ? Difficult to find out because sometimes the thing would play for hours without a glitch.
I eventually found out the 24 V PSU, the step down SMPS on board and the LDO's were all ok, all power rails remained within spec, but it still glitched sometimes. (while power was ok)
The Raspberry PI or R-pi from http://www.raspberrypi.org/ is well known these days.
It is not an accident that I have one, I have been doing Linux stuff since 1991, and professionally since 1996 I can not skip over these developments, have to keep up with the new kids. :-)
Times have changed, hardware has become very affordable, everybody knows the Arduino, Raspberry Pi and Beagle-Bone-Black (BBB). Not everybody knows the stuff that http://www.acmesystems.it/ aka Acme-Systems and https://github.com/OLIMEX/OLINUXINO aka Olimex make, so I will endorse them here.
Since I am an engineer I expect to connect switches and relays to the boards and some documentation with products, not so with the "PiFace Digital" board, it comes without serious documentation, not a even the schematic. All links on their blog point nowhere. People asked them many times, yet nowhere is the schematic to be found.
I finally found some info after hours of google-work, someone made a copy! https://github.c…