LX200 Classic Keypad Information.

The Keypad is based on a flexible printed circuit membrane with 19 Key Functions operating to a common control...in this case 0V. Each key has its own 10K0 pull-up resistor working to +5V. The connection of the membrane to the PCB is via J3.

The pinout of J3 is as follows:- (Pin No./Key Assignment)

1/Goto. 2/Mode. 3/East. 4/Enter. 5/North.

6/West. 7/South. 8/#9. 9/#8. 10/#7.

11/#5. 12/#6. 13/#4. 14/#1. 15/#2.

16/#3.17/Guide. 18/Previous. 19/Next. 20/Common.

Recommended Keypad modifications are:-

1. Replace Tantalum Capacitor, C2 with a higher working voltage component, i.e. 10uF at 35VW. This modification must be carried out as disastrous consequences may result with the irreversible damage of the keypad membrane

2. Increase heat dissipation capacity of the 5V regulator, REG1 with the inclusion of additional heat sinking.

3. Add clamp diodes to the RX/TX data ports of U6. Use 1N4007's, their anodes connected to pins 2 and 3 of U6, their cathode's go to a local 0V. This provides some immunity/protection against hot plugging the keypad.

Return To Home Page