Wed Jul 1 11:34:48 PDT 2015

Retro-Chic Bedside Radio

Bedside radio (click for a larger image)
(Bedside radio)

While the Hacker Sovereign II is a wonderful radio, I listen to the radio shown in the image on the left a great deal more. It has some practical attributes that are hard to beat.

This is a transistor radio designed by the great German electronics designer and author, Burkhard Kainka, as a simple project to be constructed in a video cassette box. I used a plastic enclosure from Radio Shack for my version, but the effect is the same...if not better...though I say so myself!

One of the key attributes of this design is the use of a single 1.5 volt AA battery as a power source. These batteries are common and inexpensive, unlike the unusual PP9 batteries in a Hacker. The power consumption is only about 12 milliamps (mA) when the speaker is in use and about 0.8 mA when an earphone is used. (I put a 1k resistor in series with a pair of earbuds for the earphone option). With that power consumption, in earphone mode, you can expect something in the region of 100 days (see * below) of continuous operation from the radio on a single AA battery, and if you use the radio for just a few hours a day, then you will be talking about several years of use.

I used a basket weave coil rather than a ferrite rod coil antenna - because I had such a coil to hand and it seemed to work fine.

Bedside radio - circuit
(Bedside radio - circuit)

The circuit is shown on the left. As mentioned, a 1k ohm resistor in series with a stereo ear buds (conntected so that each ear bud is in the series circuit) form the earphone option (this is not shown in the diagram). There is a switch that controls the use of speaker or headphones, so that you can just leave the headphones plugged in, which is more convenient than constantly plugging and unplugging.

I also added a pair of white leds connected to a Joule Thief circuit, for lighting purposes, as shown in the photograph of the actual radio above. The Joule Thief generates a lot of radio frequency interference, so you cannot use the radio and the light at the same time, unfortunately. (I didn't think of this a priori!).

Now probably this bedroom furniture will not win too many style awards, at least not with present fashions. However, if you are interested in late night American paranormal phone-ins and ufology specials (and who isn't?) this is the radio to own.

* Here is how the ~100 days was computed. An alkaline AA battery can supply 2600 mA hours when used gently, as in this case. Hence we will have 2600/0.8 = 3250 hours of use from the radio. And 3250 hours is 3250/24 = 135 days.

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Posted by ZFS | Permanent link | File under: electronics
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