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CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Noughts & Crosses game using just two modules In the October 2021 issue of Silicon Chip, the Australian entrepreneur Dick Smith announced a competition to develop a Noughts and Crosses machine. Dick Smith mentions that he built a machine using electromechanical components in his announcement. I’d love to be able to build something like that, possibly using modern relays. But I’d need an enormously large number of them and they cost a few dollars each. I decided that something using an Arduino or Raspberry Pi would be the obvious way to do the job in 2021. More or less randomly, I decided to follow the Arduino path. An Arduino Uno and an Adafruit TFT LCD are an obvious combination; mine is a ‘plain jane’ implementation. Each of the cells of the Noughts and Crosses grid becomes a button to be pressed to indicate the move the human wants to make. My design includes an extra rectangular button at upper left to toggle who plays X to start each game. The Adafruit TFT LCD is available in two versions: V1 and V2. Adafruit supply and support only V2, but most clones are V1. If a clone is used, it is important not to use the Adafruit support library but a different library: MCUFRIEND_kbv. The Arduino Library Manager knows of this library, 76 Silicon Chip and it is easy to install, but it is necessary to do quite a lot of careful reading of fine print to persuade it all to work. I have not debugged my program for V1 clones, only for V2 TFT LCDs. I implemented the Newell, Simon strategy as published. Although I eventually got it to work, the descriptions of it are not easy to follow. I studied at least three and became thoroughly bamboozled by all three of them. There are eight components of the Newell, Simon strategy and seven of them are simple, obvious, and easy to understand. One isn’t. The problem strategy is described as “Block Fork”, but it tries to do two or maybe three jobs at once, and all descriptions have “unless...” qualifications. Because I struggled to understand the Newell, Simon strategy, I tested my implementation often. I found mistakes often. I’m reasonably confident that the program submitted never allows a human to create a fork and consequently always forces a draw, unless it wins. An Excel file is available to confirm this. The Adafruit examples demonstrating the touchscreen don’t mention debouncing, but it is essential. Each touch sends a stream of X and Y coordinates of many touches, not just one. Simple delays don’t flush the redundant points out of the FIFO. I read Australia's electronics magazine several examples to discover how to combine an appropriate delay while flushing the buffer to avoid unexpected touch events. Although the Adafruit library includes several font sizes, they must be integers, and I found that size 1 is too small but size 2 is too big. Ideally, I’d like size √2, but it is unavailable. For most text, I’ve used size 1 even though that is a bit small. I’ve used size 2 for the game’s name at the top of the screen and size 3 for the Xs and Os played within the board cells. A box at the top left advises who is X and who is O. This box is touch sensitive. If it is touched at any time, including during a game, it will toggle who is X and O, and start a new game, aborting the game in play if necessary. If a game is won, it is traditional to draw a line through the winning row, column, or diagonal. I don’t do exactly that; instead, I change the colour of the text in the winning cells to white. Note that the computer doesn’t attempt to vary its moves. After a few games, it becomes a bit predictable. The software sketch (NaughtyCross. ino) is available for download from siliconchip.com.au/Shop/6/92, along with the Excel spreadsheet demonstrating that it will play a perfect game. Keith Anderson, Kingston, Tas ($70). siliconchip.com.au