Work the world on a 555
Over the years the humble 555 timer has been used in so many unexpected places, but there is a project [Frank Latos] which we think is a first. On a piece of stripboard are a pair of 555s, and instead of the usual passives there is a set of LC circuitry. This is not a timer, rather it is a CW (Morse) transmitter for the 80 meter amateur radio band.
A 555 is configured as a feedback oscillator via a toroidal transformer with a tuned circuit to adjust the frequency of oscillation. The other takes an inverted input from the oscillator to produce complementary push-pull outputs from the two 555s, which are fed to another transformer which in turn feeds a low-pass filter and hence the antenna.
Free-running square wave oscillators of this type aren’t unusual for the lower HF bands, but we believe this is the first 555 design we’ve seen. As stated it doesn’t produce much RF power, but remembering the half decent motor drivers using a 556 dual timer, we think selecting one of the more powerful 555 variants might yield a little more punch. We salute his creativity though and hope he can get that all-important journal entry to prove it works.
If you’re curious about low-power radio operation, that’s something we’ve already explored.