The Philips PM5139 is not famous. It won no great victories on the battlefield, nor was instrumental in changing the political landscape. It was just a useful function generator that you might find on a workbench somewhere, doing its job quietly and relatively accurately. [doctormord] has been doing the work to reverse engineer this humble piece of hardware.

The PM5139 is poorly documented; the only existing service manual out there is for the PM5138A, a less-capable sister model. Hence, there was some value in reverse engineering the device to understand it better. Work started with two EPROM dumps capturing what Philips put in the box all the way back in the early 1990s. From there, the code was examined and tinkered with until [doctormord] felt confident to modify it and improve upon what was already there. This was achieved with the aid of an 8051 emulator that could run the code to make it obvious what was going on. The result was a custom “V2.0” firmware that adds six arbitrary waveforms to the function generator and the ability to play simple music, amongst other tweaks.

We love to see old hardware given new functionality, even decades down the line, and we love some good reverse engineering, too. Video after the break.

Over the centuries there have been an incredible number of purported medical devices released onto the market, with some having more outrageous claims than others. Released in the 1910s and produced into the 1920s, the Farador electrotherapeutic device claimed to be a thermoelectric device that would cure all disease conditions. In a recent video over at the [Our Own Devices] channel we get an in-depth look at this device and its usage instructions.

On the Smithsonian’s website you can see the version they’ve got. It’s not identical, but the working principle remains the same — after bypassing the whole ‘is this the right treatment’ questionnaire because it’s a cure-all device, you take the main metal device and its connected electrodes out of the box.

Unlike similar devices of the era that applied an actual electrical current using batteries or similar, this Farador purportedly uses thermoelectric power generation, but there’s no clear hot or cold side to what would be the generator. Despite this, about 20-30 mV can be measured across the electrodes, so surely it’s working?

As it turns out, the Farador is just one of many fake medical devices that cloned the original Electropoise. Naturally such devices have been disassembled by many over the past decades, and as it turns out they are all empty inside, or at least devoid of any mechanisms. Much like many of such fake medical devices today, they mostly bank on the placebo effect. This placebo effect can be so strong that it’s even a confounding factor in real medical trials and medicine.

The more involved and complex the purported medical treatment seems, the stronger the effect tends to be. For the Farador the complex instructions, apparently high-tech thermoelectric generator and such all help to create the illusion and could thus be construed to be the main feature of this product.

A pyrotechnic charge is set off by passing a high voltage through a filament within it, melting the filament and igniting the charge. We could think of a variety of circuits that could do this, but perhaps we wouldn’t have come up with [Michał Słomkowski]’s solution. He’s used the ringer crank generator from an old military field telephone. It’s an old project he’s shared with us due to its recent republishing on his website.

The basic principle is simple enough, winding the generator charges a capacitor bank through a bridge rectifier. Then a thyristor is used as the trigger device, dumping the contents of the capacitor into the filament. But the full circuit has a couple of refinements. There’s a charge indicator circuit using a couple of Zener diodes and an LED, and a filament tester which passes a non-triggering current through the filament from a 9 volt battery. We like the use of an over-the-top high-current thyristor, no doubt what he had in his junk box.

Perhaps it’s a symbol of how far technology has moved, that today it’s surprisingly rare to find a bridge rectifier or a thyristor, and building this device today would involve a microcontroller and probably an AliExpress inverter module as a matter of course.

Meanwhile, should field telephones interest you, we’ve been there before.