手可摘棉花

555 timer: 4MHz (80 meter band) CW transmitter

Overview

Might not be an actual working transmitter, but it does produce a few mW of RF power at 4 MHz using only two LMC555s. Principle of Operation (see attached simplified schematic): At lower operating voltages, the flip-flop (TR) input of the LMC555 can be used as an inverting comparator input to control the output of the device. This requires the Threshold (TH) input to be active (high). This circuit applies a DC bias at the switching threshold of TR and superimposes a small AC feedback signal to create an oscillator. An inverted version of the same signal is applied to the second LMC555 to produce two complementary open collector outputs (the device's discharge output). The output is then connected as a standard push-pull RF amplifier. The TH input is used as the enable input to key the transmitter.

Blockdiagram

Design Files

2021-Hackaday-555-Contest-main

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Update:2025-06-18 21:38:54

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