Found in a 1990s Popular Electronics, this circuit produces a tone on a small speaker. The keyer directly controls the power supply.
In the figure we have the typical circuit of a Baxandall tone control applied to an operational...
August 2017 - Microchip's new ATtiny1617 8-bit AVR microcontrollers running at 20 MHz and 16 kB...
This Signetics circuit uses a double 555 (556) to generate tone bursts at frequencies determined by...