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LCD Extension Board

This board turns MyNOR into a "real" computer. It adds a display, keyboard, sound, real-time clock and a temperature sensor to the MyNOR base board. With this board you do no longer need the serial terminal to communicate with MyNOR. This board allows you to use MyNOR alone, e.g. for simple games like Tic Tac Toe, Minesweeper or a car driving game. MyNOR automatically detects the presence of the board and displays a menu that allows you to load one of eight programs from the EEPROM.

LCD extension board

The keypad is read out in a multiplexed manner to reduce the number of required I/O pins. The LCD is controlled in 8-bit mode to increase the transfer speed. The real-time clock chip and the temperature sensor are connected via I2C. The sound output is as simple as possible: A D/A-converter (connected via SPI) controls a VCO chip that generates frequencies in the range from 262 Hz to 2093 Hz (= three octaves).

LCD extension board without LCD

As you can see, a small 32 Ohm speaker is mounted on the board. There is also an additional IC (74HCT00) that is used as speaker driver and for muting. The right-angled header on the left exposes the I2C and SPI bus, and enables the connection of other peripheral devices to the board. The RTC (real-time clock) has three functions: First, it is a clock. Second, it is used to generate a 1 Hz signal as time base for the MyNOR computer (MyNOR can use it to "simulate" 2 timer interrupts per second with it), and third, the clock chip is used to calibrate the sound output because it can be configured as an event counter that is used by the calibration software for frequency measurement.

Schematics and BOM

Click on the schematics to see it in full resolution (PDF).

You can get the design files in the download section.

All components can be sourced from Reichelt, Mouser or Digikey.

A great PCB manufacturer is JLCPCB (China). All you have to do is upload the zip-file that contains the Gerber data to JLCPCB.

Note: BudgeTronics is selling a complete kit with all required components and the PCB.

BAT1battery holder for CR2032
C1 C2 C4 C5100 nF
C3optional, for RTC tuning
C610 nF / 5%
C7 C810 µF / 16V
C91 µF / 16V
D1 D2 D3 D4 D5 D6 D7 D8BAT41
J1 J2Header 2x10 pin, 2.54mm
J3Header 1x8 pin, 2.54mm, right angle
J4USB type B mini connector
R110 kOhm
R2 R322 kOhm
R433 kOhm
R522 Ohm
R6220 Ohm
SP1Speaker 32 Ohm
SW1 - SW15 (15 pcs)push button 6x4.3mm
TR1250 Ohm, Piher PT6S
TR2 TR310 kOhm, multi-turn trimmer
TR410 kOhm, Piher PT6S
U1LCD 4x20
U3TMP75AIDR (or LM75)
U4CD4046BE (!)
Y1Crystal 32.768 kHz