The Drake TV daughterboard is a very simple circuit, based around the PIC16F628A, although I made a version using the PIC16F688 as well. The board uses a composite video and RCA audio output, has the usual 78L05 power regulator and uses a 9-pin sub D connector to hook up to the old Drake motherboards, which will be described at another time. The daughterboard accepts specially coded input of characters, and outputs them as a signal to the TV, also handling audio.
The choice for a PIC16F628A was very deliberate, and the resulting code ONLY runs on this device. A larger memory actually causes the timing to go off, and such a device would actually have less functionality (which is the case for the PIC16F688). 18F devices could of course perform similarly, but they would be more expensive. With the current circuit you can output TV from your product for less than $2.
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