Make Snake run on a salvaged seven-segment display

Arduino Uno Rev3

Soldering iron for salvaged panel connections

Arduino IDE

Salvaged SM1628B seven-digit LED panel

<html><body><h3></h3><h3>The idea</h3>We wanted to make Snake run on the worst display we could find. We started with a Sony dot-matrix VFD, but its 525 pixels still seemed far too useful. A salvaged seven-digit, seven-segment panel gave us just 49 bars to work with. That seemed more appropriate. This project treats each bar as one position for the snake. The joystick controls its direction, a blinking bar represents food, and the snake grows when it eats. It is the familiar game, with considerably less room to move around. The video shows the build, the unusual movement rules and us playing it: Watch the build: https://www.youtube.com/watch?v=3hOSXTLOnHo The complete SM1628/SM1628B tutorial and source code: https://github.com/emsyscode/sm1628-arduino also covers using the driver without the game. You can stop after the display tests if you simply want to reuse a similar panel. <h3>Before copying our wiring</h3>Our build uses an assembled SM1628B panel, not a bare driver IC and a newly wired display. Another panel can use the same driver while connecting its digits, segments and connector differently. Identify your panel's supply and connector, then map its lights before copying our lookup table. The display commands taught in the repository apply to both SM1628 and SM1628B. Their oscillator connections and protection specifications differ; the variant guide: https://github.com/emsyscode/sm1628-arduino/blob/main/docs/driver-variants.md explains those differences. The hardware demonstration here uses our SM1628B panel. This is not a promise that every panel carrying either chip will work with an unchanged sketch. <h3>Components</h3>Component — Quantity — Used in this build Arduino Uno — 1 — ATmega328P, 16 MHz Assembled SM1628B LED panel — 1 — Seven numeric digits plus predefined symbols Analog joystick — 1 — Industrial unit with X/Y potentiometers; Z unused Regulated external supply — 1 — +5 V DC, suitable for the actual connected load Resistors — 7 — 1 kΩ: three display signals and four joystick track ends Resistor — 1 — 10 kΩ for the buzzer transistor's base Resistor — 1 — 680 Ω in the START switch-to-ground path Normally open push-button — 1 — START Capacitor — 1 — 10 nF across the START switch Electrolytic capacitor — 1 — 470 µF, rated 35 V NPN transistor — 1 — 2N2222-family buzzer driver; identify its actual B/C/E leads Active buzzer — 1 — DC on/off type, used with the +5 V supply Breadboard and connecting wires — As needed — Prototype connections Use Arduino IDE and select Arduino Uno. No external Arduino library is needed. The sketches use ATmega328P port registers and are not drop-in programs for every board carrying the Arduino name. <h3>1. Connect only the display first</h3>Our panel uses an external +5 V supply. Connect the supply ground, panel ground and Uno GND together. Keep the external +5 V rail separate from an independently powered Uno's +5 V rail. Connection — Destination Uno D7 through 1 kΩ — Panel DATA, labelled DA or D Uno D8 through 1 kΩ — Panel CLK or C Uno D9 through 1 kΩ — Panel STB or S External +5 V — Panel +5 V input Common GND — Panel GND Panel IR or R signal — Leave unconnected Connect the 470 µF capacitor across the external supply: positive to +5 V, negative to GND. Its 35 V marking is its voltage rating; the supply remains +5 V. Follow connector labels, not the physical order or wire colours in a photograph. The connection guide: https://github.com/emsyscode/sm1628-arduino/blob/main/docs/01-connect.md includes two photographed connector orders. Keep the joystick, START button, buzzer stage and unrelated peripherals disconnected during the initial display-only tests. The working examples retain whole-port initialization: PanelDemo drives D0–D13 as outputs; ManualMap restores D0 for serial input but still drives D4. Attach the START network only when running a sketch that configures D4 as an input. <h3>2. Find which bits control which digits</h3>Download the repository ZIP: https://github.com/emsyscode/sm1628-arduino/archive/refs/heads/main.zip and extract it. Open firmware/ManualMap/ManualMap.ino, select the Uno and correct port, then upload. Keep any headers alongside their sketch files. Open Serial Monitor at 9600 baud, using Newline or Both NL &amp; CR. Wait for READY. Send: column 0 7 Then send n on its own line to advance, or p to go back. You must select the initial column before using next/previous. The final argument above is 7, the numeral being drawn; it is not the number of digits to scan. On our panel, the first command draws a 7 on the leftmost numeric digit. The next result is the second digit, followed by the fourth. The third digit appears later, after a symbol group. Write down the result of each raw column instead of assuming that the order matches the physical display. Our numeric columns, from left to right, are: constexpr uint8_t kDigitColumns[] = {0, 1, 7, 2, 3, 4, 5}; These are RAM column numbers, not connector pins or the Grid labels on the reverse-engineering drawing. After selecting a column, digit 8 lights all seven bars for that column. A 7 only tests three bars, so it cannot establish a complete segment or symbol map. The bit commands let you isolate individual memory bits. See the mapping procedure: https://github.com/emsyscode/sm1628-arduino/blob/main/docs/manual-mapping.md for the complete process. Once your map matches ours, ordered, followed by n, walks through the numeric digits in physical order. This command uses the built-in lookup; it does not discover the order automatically. <h3>3. Why this panel needs a different memory map</h3>The driver can control seven digits with up to ten segments each. This panel swaps the roles of the digit and segment connections, using a common-anode arrangement to control ten groups of seven lights. Seven groups are numeric digits; the remaining three control predefined symbols. The driver still receives its native seven-digit/ten-segment mode command. What changes is the way we construct the display bytes. In our transposed arrangement, the bars belonging to one physical digit are spread through the frame rather than sitting together as one ordinary digit pattern. Our sender writes a complete 14-byte frame for each update. This keeps the map straightforward; it does not mean that the chip forbids individually addressed writes. The memory guide: https://github.com/emsyscode/sm1628-arduino/blob/main/docs/04-memory.md explains the commands and byte layout. If another panel changes only the physical digit order, its lookup table can be adapted. If its segment order or native/transposed wiring differs, those parts of the frame construction must be adapted as well. Merely replacing seven column numbers is not a universal conversion. <h3>4. Check numbers and effects</h3>For a panel matching our map, upload firmware/PanelDemo/PanelDemo.ino. Each numeric digit should count from 0 to 9, starting on the left, without lighting the symbol groups. For more display tests, upload firmware/PanelShowcase/PanelShowcase.ino, keeping its headers together. Open Serial Monitor at 115200 baud, with Newline or Both selected. Send one command per line: Command — Result on our panel digits — An 8 sweeps through the numeric positions count — All numeric digits count together value 9995, then carry — Count upward through the carry into 10000 bars — Matching bars light across the digits demo — Run the display-effects sequence once stop — Blank the display and cancel the effect PanelShowcase also has a scripted Snake demonstration, selected with snake. That is a programmed replay, not joystick gameplay. Upload PanelSnake for manual play. <h3>5. Add the joystick, START button and buzzer</h3>Switch power off before changing connections. Follow the complete circuit diagram: https://github.com/emsyscode/sm1628-arduino/blob/main/docs/circuit-inventory.md and identify your joystick terminals and transistor's physical leads. For each joystick axis, connect: External +5 V — 1 kΩ — potentiometer track — 1 kΩ — GND | wiper Connect the X wiper to A0 and the Y wiper to A1. The two resistors per axis are external to the joystick. Z/rotation is unused. Reversing the track-end connections reverses the voltage change, so check direction labels before playing. The START network is: D4 — normally open switch — 680 Ω — GND Place the 10 nF capacitor across the switch itself. PanelSnake uses the Uno's internal pull-up and software debounce; the 680 Ω resistor is not an external pull-down. For the active buzzer: Connection — Destination D11 — Through 10 kΩ to transistor base Transistor emitter — Common GND Transistor collector — Buzzer negative Buzzer positive — External +5 V The active buzzer generates its own pitch. The firmware switches the transistor on and off instead of using tone(). A 2N2222-family part's package lead order must be checked for the actual transistor being used. Reference Snake circuit (diagram supplied below). <h3>6. Upload and check the controls</h3>Open firmware/PanelSnake/PanelSnake.ino, keeping SnakeGame.h in the same folder, select Uno and upload. This sketch reserves D4 for START and D11 for buzzer control; its compatibility setup also drives the other pins in D1–D13 as outputs. Keep unrelated peripherals off that bank. Open Serial Monitor at 115200 baud. Keep the joystick centred for the one-second calibration. Expect centre readings followed by READY. Before starting a round: 1. Send m to enter the 49-bar test. Expect the top bar of the leftmost digit. 2. Send n to step through its top, upper-right, lower-right, bottom, lower-left, upper-left and middle bars, then continue across the digits. 3. Send j to enable joystick reports. Move in each direction separately and check the reported label. Let go and check that it returns to CENTRE. Send j again to stop reports. 4. Press START or send s to play. If the axes are exchanged or reversed, check kSwapAxes, kReverseX and kReverseY near the top of the sketch. Change the appropriate setting, upload again and recalibrate. Send c to recalibrate with the joystick centred. The separate JoystickTest sketch is available for bench readings. Its slower reporting interval makes the numbers readable; it is not the game's input polling interval. <h3>7. Play on the figure-eights</h3>The snake starts with three bars. The food blinks on a free position. Eating it adds one bar and one point. Running into the body or leaving the available path ends the round. Direct reversal is ignored, and releasing the joystick does not stop movement. The gaps between digits add no extra positions. At an up/down turn, the snake uses the first side it reaches before crossing the gap. If food is on the vertical bar immediately beside that side, turning toward it will not collect it. You have to come around from the opposite direction. That small decision makes the display even less suitable than we initially thought, which was rather the point of the project. After a collision, the snake freezes and blinks, then the panel shows approximate GAME, OVER and SCORE lettering with the score. Release and press START for another round. A press during play does not reset the current round. The individual central colon is not selected by this version of the map. To change movement speed, send a complete line such as: pace 300 This means one move every 300 ms. Lower values are faster; the accepted range is 50–2000 ms. The default is 450 ms. Speed persists across rounds until reset and is independent of how far you push the joystick. <h3>If it does not behave as expected</h3>- No display: check the panel's required supply, common ground and DATA/CLK/STB labels. A connector copied from another panel may be wrong. - Wrong digits or symbols: return to ManualMap. Matching driver names do not establish matching panel wiring. - Next reports an invalid selection: in ManualMap, send column 0 7 before n. In PanelSnake, start its bar test with m before n. - Wrong joystick direction: check j reports, wiring and the orientation settings, then recalibrate. - No sound: check that the buzzer is active, powered correctly and connected through the transistor stage. D11 is the control signal, not the buzzer's direct supply. - Letters look strange: seven-segment GAME/OVER/SCORE lettering is approximate. Serial output also reports the score. The repository troubleshooting guide: https://github.com/emsyscode/sm1628-arduino/blob/main/docs/troubleshooting.md and game guide: https://github.com/emsyscode/sm1628-arduino/blob/main/docs/snake-test.md cover the controls and expected results in more detail. <h3>Code, diagrams and the finished build</h3>The repository: https://github.com/emsyscode/sm1628-arduino contains the small display example, manual mapping tool, effects showcase, joystick test and playable game. Code and documentation are MIT licensed. The build video: https://www.youtube.com/watch?v=3hOSXTLOnHo shows how we arrived at this rather unnecessary game and how it turned out when we played it. It worked much better than I expected. We could probably still find a worse display. <figure><iframe src="https://www.youtube.com/watch?v=3hOSXTLOnHo"></iframe></figure><figure><img src="https://raw.githubusercontent.com/emsyscode/sm1628-arduino/main/docs/images/snake-connections.svg"/><figcaption></figcaption></figure>Complete reference circuit. External +5 V supply; common ground with the Uno.<figure><img src="https://raw.githubusercontent.com/emsyscode/sm1628-arduino/main/docs/images/driver-and-panel.svg"/><figcaption></figcaption></figure><figure><img src="https://raw.githubusercontent.com/emsyscode/sm1628-arduino/main/docs/images/header-5v-ir-gnd-clk-stb-data-labelled.jpg"/><figcaption></figcaption></figure><figure><img src="https://raw.githubusercontent.com/emsyscode/sm1628-arduino/main/docs/images/header-v-r-g-d-c-s-labelled.jpg"/><figcaption></figcaption></figure></body></html>

Make Snake run on a salvaged seven-segment display

An Arduino Uno, an industrial joystick and 49 LED bars make a surprisingly playable game on a rather unsuitable display.