The Circuit itself is fairly straightforward the MC145436 circuitry is straight out of the data sheet. It uses a Crystal locked oscillator based around a 3.579 MHz colour burst Crystal and generates a 447.4 KHz clock which feeds the Oscillator input on the PIC16F84. When the MC145436 Receives a valid tone it raises the DAV pin, when the OE lead goes High the output buffer on the MC145436 goes low impedance and presents the last data it received on the Data pins (1,2,14,13) the OE line also enables the output from the 74LS241 and the processor also reads the state of the 4 Push buttons.

R5 is a pullup Resistor for the open collector output RA4 and R1-4 are pull down Resistors for the Pushbuttons.

Although the 74LS241 is an 8 bit buffer only 4 bits are used - although smaller buffers are available the pin out of the 74LS241 makes the PCB easier to design and the cost for the 74LS241 is the same if not less than the alternatives.

The 16F84 decodes the Data from the MC145436 into ASCII, stores it in a Rotary buffer and then updates the LCD Display. In fact most of the work in this Project is done by the Code in the Processor.

Power for the display can be regulated using a 7805 voltage regulator or if a 5V supply is already available the regulator can be left off an power connected via the +5V connection.

The Source Code is available for Viewing or Download, however my original code was on a Laptop which was stolen so I had to read the code from an already programmed 16F84 and the comments and Pseudo code in this listing are based on my memories of how the code worked - in other words there may be some errors.