TURN AN OLD TV INTO A STANDALONE LOGIC ANALYZER

By using a simple PIC16F84


4-input capture, up to 600 kspl/s

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This is a good way to reuse an old CRT color TV instead of trashing it (like many people do now), particularly if this TV is quite small and gives the opportunity to get a standalone (PC free) and portable equipment. A PIC 16F84 microcontroller is the main part of the hardware extension to be plugged onto the TV via the SCART socket or even mounted inside the TV
(like in my personnal example).





What does this quite simple hardware extension

The microcontroller handles all the required tasks:
- Signal change detection (trigger)
- 4-way signal capture in single shot mode
- RGB video signal generation (625 lines, commonly nicknamed "PAL") to display a grid with 4 colored signal traces

The trigger can be assigned to one selected channel or to anyone (the first change on any input triggers the capture). The "telltales" visible at the bottom of the screen allow to see what is the current capture rate (yellow telltales: 6 capture speeds possible), what is/are the triggering input(s), and if the analyzer is armed or triggered.

RGB signals are simply obtained with resistor networks connected to microcontroller output ports (see schematic) for being able to control with less software resources as possible the three separate RGB signals plus a soft grey (used for grid display) by controlling simultaneously with one port the three RGB components at a low level.

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SCHEMATIC