Source: https://mokxi.com/seven-segment-display-simulator Updated: 2026-10-25 Simulator # A 7 segment display simulator that counts Mokxi is a free online 7 segment display simulator that runs in your browser, with nothing to install and no account needed. An Arduino Uno drives a common-cathode seven-segment display straight from eight pins, each segment through its own 220 ohm resistor, and counts from 0 to 9 once a second. Start building free or see the display part - 455 parts on the bench - 43 boards running now - 1.00x real time, on every board Click to open it in the editor It counts 0 to 9 and the dot blinks on odd digits. Click the circuit to open it in the editor. ## What you can do here In the circuit above, or in the editor it opens. - Watch each digit drawn from a one-byte segment pattern - Change the font table and make letters or your own symbols - Switch the display to common anode and see what has to change - Pick red, green, blue, yellow or white segments - Move up to a four-digit display, a TM1637 or a MAX7219 - Drive one from logic chips alone with a CD4511 decoder ## What the running circuit shows Seven LEDs and a byte per digit. Each segment is an LED, so a digit is a pattern of lit segments. The sketch keeps the ten digits as one byte each, segment a in the lowest bit (0x3F for 0, 0x06 for 1, up to 0x6F for 9), and walks the seven bits setting each segment’s pin: a on pin 7, b on 6, c on 5, d on 11, e on 10, f on 8 and g on 9, with the dot on pin 4. In the engine the display shows 0 to 9 a second apart, the serial monitor prints each digit, and the dot is lit on the odd ones. Seven resistors, one per segment, is the right way to wire one: every segment gets the same current whatever the digit. The cheap way, one resistor on the common pin, makes an 8 dimmer than a 1, and the electronic dice project wires it that way so you can see the difference. ## The truth table, digit by digit Which segments each number lights, and the byte for it. Segments are named a to g clockwise from the top, with g across the middle. With segment a in the lowest bit, as in the running sketch, the ten digits on a common-cathode display are: 0 lights a, b, c, d, e and f (0x3F); 1 lights b and c (0x06); 2 lights a, b, d, e and g (0x5B); 3 lights a, b, c, d and g (0x4F); 4 lights b, c, f and g (0x66); 5 lights a, c, d, f and g (0x6D); 6 lights a, c, d, e, f and g (0x7D); 7 lights a, b and c (0x07); 8 lights all seven (0x7F); and 9 lights a, b, c, d, f and g (0x6F). Letters come from the same table. The hex digits are A (0x77), b (0x7C), C (0x39), d (0x5E), E (0x79) and F (0x71), with b and d in lower case so they do not look like 8 and 0. Letters such as K, M, W and X have no shape on seven segments that reads clearly. On a common-anode display a segment lights on LOW, so every bit is inverted. ## Displays in the parts bin From one digit to eight, with or without a microcontroller. The single digit comes common cathode or common anode. The parts bin also has a four-digit display you multiplex yourself, a TM1637 module with its own driver chip, an eight-digit MAX7219 module, an HT16K33 backpack, and a CD4511 BCD decoder that drives a digit from four switches with no code at all. 7 segment display with Arduino Four digits, multiplexed The TM1637 module BCD to 7 segment, no code ## Questions Is it free? Yes. The circuit on this page, every part in it and the editor it opens in are on the free plan, with no card. Do I need an account? No. The circuit runs the moment the page does, and the editor opens without one. A free account is only for saving a project to the cloud and sharing it by link. Common anode or common cathode? Both. Set the part’s common property. On a common-anode display the common pin goes to 5 V and a segment lights when its pin goes LOW, so the sketch inverts every bit. What is the 7 segment display truth table for 0 to 9? With segment a in the lowest bit, 0 to 9 are 0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F and 0x6F on a common-cathode display. The running sketch keeps exactly that table, one byte per digit. Can I simulate a 4 digit 7 segment display? Yes, with the four-digit part and a multiplexing sketch, or with a TM1637 or MAX7219 module that does the multiplexing for you. Can I build one without an Arduino? Yes. A CD4511 decoder takes a four-bit number from switches or a counter chip and lights the right segments, and the BCD decoder page has that circuit running. ## More simulators Each one opens on a circuit that is already running. 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Nothing to install, and no account needed. Start building free Open the editor