$5 Radio… RETURNS!

Everyone remembers my $5 radio! If not, rather than adding on to that entry from almost two years ago:


Any way, I have been thinking almost since I built that power supply that it is too bulky. At first it was kind of neat to show off, it looked original and unique, but it’s hard to put it behind a shelf or on a desk (the reason I bought the radio in the first place is because it would go well as a shelf for a flat panel monitor) and it was cumbersome or impossible to deal with. I thought about encasing the power supply in Plexiglas but this would be expensive and, frankly, more work than I think it’s worth.

So! I took apart the radio to see what was inside. Oddly enough I hadn’t done this yet. My original idea was that I could use the power button on a relay of some sort to make sure the transformer, wherever I decided I wanted it to go during this rebuild, wouldn’t be energized all the time. I still have to pay the electric bills!

There was a lot of space inside the radio! AND when I cut through the wires on the switch I found out a few interesting things. The first was this was simply a switch: open or closed. Easy to work with. The second was that the radio uses 28V AC as logic, at least for turning itself on and off. I don’t think the switch handled all of the power, just simply told the radio when to look like it was turning on, which I am only guessing at based on the fact that the radio has memory buttons and no internal battery. It would need some sort of power all the time (in a standby mode or similar).

I decided to make it extremely simple. I ran 120VAC in to the switch, then back out of the radio about four feet to the primary side of the transformer (and I attached the neutral here as well). The extra wiring means the switch controls the transformer, and no energy is wasted in hysteresis and core losses in the transformer when the radio is off. Then I ran (existing) wire from the secondary of the transformer inside the radio. From there I implemented my original voltage divider scheme, only instead of the resistors screwed in to a wooden plank they are JB Welded to the underside of the plastic case and soldered together. This is a much better construction: the JB Weld will hold better and will insulate the plastic from heat transfer (theoretically) and the solder joints are much lower resistance than what previously existed. I also eliminated one switch while keeping the same functionality, and there’s no sketchy “HOT!” labeling to scare off the Safety folk if I were to HYPOTHETICALLY use this radio in my office at work…

When it’s all back together, the transformer sits comfortably far away from the radio, and the radio looks like it was meant to be there! This is also a perk because I currently have a disassembled satellite dish, unfinished amplifier, and a random microcontroller project going on in the same area. Feel less cluttered and/or nerdy! Well, it’s the best I can do. The only thing that I am not sure about is whether or not the switch can handle 120VAC. There was nothing on the switch indicating it could or could not, so I decided to take a chance. We’ll see how it goes!

OH! I also added a fuse. Just in case. You never know.

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