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.

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).

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.

Reference Value BAT1 battery holder for CR2032 C1 C2 C4 C5 100 nF C3 optional, for RTC tuning C6 10 nF / 5% C7 C8 10 µF / 16V C9 1 µF / 16V D1 D2 D3 D4 D5 D6 D7 D8 BAT41 J1 J2 Header 2x10 pin, 2.54mm J3 Header 1x8 pin, 2.54mm, right angle J4 USB type B mini connector Q1 BS170 R1 10 kOhm R2 R3 22 kOhm R4 33 kOhm R5 22 Ohm R6 220 Ohm SP1 Speaker 32 Ohm SW1 - SW15 (15 pcs) push button 6x4.3mm TR1 250 Ohm, Piher PT6S TR2 TR3 10 kOhm, multi-turn trimmer TR4 10 kOhm, Piher PT6S U1 LCD 4x20 U2 PCF8583T U3 TMP75AIDR (or LM75) U4 CD4046BE (!) U5 MCP4921 U6 MCP1702-3302 U7 74HCT00 Y1 Crystal 32.768 kHz