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[burakkucat]

A few days ago, a certain eBay listing caught my eye. The textual description stated --

Sorry don't know much more other than it comes with power and lights up!
99p start and no reserve.

A working 'wotsit', complete with PSU, for £0.99 . . . 

It was delivered to The Cattery yesterday morning and I first decided to concentrate on the PSU. Both the 'wotsit' and the PSU had been wall mounted and, clearly, the wall had been repainted in magnolia on more than one occasion. Three screws were undone and the PSU casing was removed. The two parts of the casing were put into hot soapy water to soak. The PSU really impressed me. So much so, that I took a photograph of its innards. (Attached below.) A fuse, a transformer, four diodes and a capacitor. When powered up, it was audibly silent and, not being a switching mode PSU, was also RF silent. Without a load, the output measured 14.5V DC.

A brief scrubbing with a nail brush removed all traces of the magnolia paint from the casing and, when dry, the two halves were also photographed. (Also attached below.) From the label, the PSU is designed to provide 1000 mA at 9V DC. It is yet to be checked under load conditions but I have no doubt that it will be up to the task. Also from the label, I note that the PSU was manufactured in Germany and it has a definite Teutonic build quality about it. From the other photograph of the casing, we can see that the PSU is a Beattie Power Unit 1A dating from the Piper logo era.

Details about the 'wotsit' will be posted in this thread at a later date. 

[Black Sheep]

I'm posting this knowing i'm going to be shot down in flames by the electronic whizzes. I have an ONC in electronics from decades ago, but have never put it into practice, never had to really. So with that in mind, my memory recalls that 4 diodes, when put in a certain formation, create a 'Wheatstone bridge', and that some capacitors are used to 'smooth' the ripple on the DC output

Pure guess work, but need to keep myself occupied !! 

[burakkucat]

Spot-on, B*Sheep! (Apart from your attachment of Charles Wheatsone's name to a common or garden bridge rectifier.) 

[Black Sheep]

Really Wow, who's da man !!!  . Ha ha, only jesting, but am happily smug that my guesswork was in the ball-park. Cheers, B*Cat.

[ColinS]

Yep, must be just-about the simplest form of AC-to-DC PSU: a step-down transformer, with a full-wave bridge rectifier and ripple (or smoothing) capacitor, as BS said.  Wot? No fuse on the output side? 

You (still) own a trim-phone as well, and you _are_ Beattie!  I claim my 99p! 

[burakkucat]

The 'wotsit' was also dismantled down to its basic modular components and all the casing components were given the hot soapy water, nail-brush scrubbing. Photographs of the innards, PCB, etc, were taken before it was put back together.

The 'wotsit' was connected to the PSU and the latter then attached to the mains supply. The power-on self test took place and everything looked good. Application of the DMM probes to the PSU output circuitry now showed it delivering 12V DC when under load. So it looks as if I can regard it as a source of 12V DC, regardless of what the label says! I suspect that if I attach a dummy load to the PSU and gradually 'crank it up' until the full 1000 mA is being drawn, the measured voltage across the load will then be 9V DC.

As far as I am concerned the PSU, alone, was worth the £0.99 that I paid. 

[MuttyWango]

Details about the 'wotsit' will be posted in this thread at a later date. 

8) I am intrigued. I need to know all about your cheap wotsit.

[burakkucat]

8) I am intrigued. I need to know all about your cheap wotsit.

I had completely forgotten about this thread! 

Here are three external images of the 'wotsit', after the casing was scrubbed clean of magnolia paint splashes and the unit was re-assembled.

[burakkucat]

An image of the main PCB and a close-up of the fibre-optic connections, receive & transmit.