JANUARY 31, 2011 (See also Companion Blog )
[Go BACK to Table of Contents] [ Next Experiment ] [ Last Experiment ]
This is actually a combination of two separate circuits. The radio consists of a receiver section and an amplifier. The diagram here is only the reciever section. First is a simple radio receiver which will power a "crystal" earplug. Such a circuits are easy in the extreme, as soon as you connect the pieces they start working by themselves. I won't detail the operation, as schematics for such radios are available with all the documentation you'd ever need. Just build one, it will work.
If you examine the first diagram, you will see that it is basically a coil and a capacitor connected to antenna and ground. It is powered by the radio waves in the air as they pass the antenna and induce a small electrical current. The coil has no "taps" and the capacitor is fixed, so the only way to "tune" this radio is to attach it to different antennas. I am probably going to use some type of variable coil and capacitor, but not right now.
The earplugs are getting hard to find--and expensive. Earplugs have a tinny monoaural sound and are falling out of production as cell phone headphones dominate the market. However, headphones require more power than can be supplied sole by the radio circuit.
Hence, my circuit contains an amplifier. Examine it closely, it is easy to understand once you recognize the components. The radio has no power supply, but the amplifier uses five volts. The weak radio signal is used to operate the single transistor base, allowing a larger current or voltage (I don't know yet) to drive a 2" speaker. This is my most ambitious project so far, please allow time for me to get it working. You may find more editorial comments at Tales From The Trailer Court which gives a less technical explanation but involves a lot more reading.
FEBRUARY 5, 2011
This project is more involved than I first imagined, but not because it is complicated. The reason is that I've taken care to study each component by itself and in combination. Wikipedia has an excellent article for novices, it is titled Electronic component . It is also a good read.
The actual radio circuit is an amalgamation of several I've tinkered with, but this time I am learning why it works. The delay at this time is finding the proper parts, many of which have fallen out of availability due to Internet radio. I just located a tuning capacitor and have not yet figured out how to connect it. It is in a plastic casing with no obvious markings.
Update April 5, 2012
This project is now on permanent hold. In the end, it was the antenna technology that got too difficult. Also, building a radio from anything but a kit is, I found out the hard way, beyond the skills of a beginner. In the end, I dismantled most of the radio parts for use with other labs. The whole radio concept was chosen largely because I had no idea what constituted a reasonable goal.
Radio is so refined, it is better to devote your energy into learning to use and code off-the-shelf gear, like the X-Bee, a short range FM controller. While a simple radio can be hand-made from spare parts, I now question if anything more complicated is worth the effort. Mind you, as the nearby picture shows, when the radio was on the agenda, we built some exceedingly high quality parts. Like this copper antenna coil.
Go BACK to Table of Contents
