Want to make your own CW keyer? Here you go. Do you need a trainer that can decode the output of a CW paddle and display it on a LCD display? Easy. Do you want to create a beacon keyer for ARDF? No problem! Do you need the chip for other functions (like controlling the VFO)? The library can be integrated into other code.
To encourage other HAMs to contribute their code to the project I have released it as open source on Sourceforge. A binary version for the ATTINY45 controller is published there as well.
Once the AVR chip is programmed, it can be used in a minimal configuration as detailed in the above picture (click on it!) In a RF sensitive environment the power supply and the keyer lines should have blocking capacitors towards ground (10-100nF).
The TX keyer output (Pin 5) can deliver either a positive or negative logic 5V signal (programmable at run time) that can source/sink 20mA according to chip specifications. The signal should be used to drive the TRX keyer circuitry as required. A NPN transistor is shown as an example in the schematic.