{"id":1602,"date":"2023-11-10T19:00:13","date_gmt":"2023-11-10T19:00:13","guid":{"rendered":"https:\/\/www.adrian-smith31.co.uk\/blog\/?p=1602"},"modified":"2025-08-08T20:46:43","modified_gmt":"2025-08-08T20:46:43","slug":"6_digit_clock","status":"publish","type":"post","link":"https:\/\/www.adrian-smith31.co.uk\/blog\/2023\/11\/6_digit_clock\/","title":{"rendered":"Build a large 6 digit clock using 1.8″ + 0.8″ LED displays and TPIC6B595 shift registers"},"content":{"rendered":"

The project<\/strong><\/p>\n

I recently bought a few LED displays as a job lot which were parts for fruit machines; the type you see in the local pub and after testing them I found that they had a nice bright red \/ orange colour to them and decided to use them for a large clock project. As I have not made anything for a while and had some spare time on my hands I thou\"\"<\/a>ght I’d need to brush up on my PCB design skills and C++ coding skills. Hence this project – a large LED clock which uses 1.8″ high digits for the hours and minutes and the seconds is displayed on 0.8″ 7 segment displays. It is controlled by an ATMEGA168P microcontroller and uses TPIC6B595 shift registers to drive the common anode displays. A DS3231 high precision RTC completes the electronics. It is a large PCB measuring 270x120mm and can easily be seen from 30 feet away making it suitable for large workplaces or people with limited vision. The clock is powered from a 12V regulated power supply which can supply 800mA or more. A fuse and reverse polarity protection diode helps to prevent incorrect power supply connection from damaging the components. Finally three buttons are used for setting the time. There is provision on the PCB for a 4th button which could be used for something else if I wanted to add extra features later or with the code being open source you could make use of it yourself should you make one.\"\"<\/a><\/p>\n

This project was sponsored by PCBway<\/a> who kindly offered to make the PCB’s for them. As I have already made the prototypes using boards from JLCPCB I decided to take up their offer and made a slight design change to the PCB layout. I plan to sell these PCB’s along with the remaining version 1 PCB’s on eBay \/ Tindie so you can make your own if you wish. Please see the links to the right for my eBay store where you can purchase one along with a completed, assembled PCB which I will list in the coming weeks once the button boards and new TPIC6B595 chips come into stock. The version 1 PCB’s are made in green solder mask whereas version 2 has black solder mask. The source code and schematic I will show below and also there is a YouTube video explaining how the circuit and code works.<\/p>\n

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Schematic, code, BOM and YouTube video<\/strong><\/p>\n

\"Schematic\"<\/a>
Schematic for the ATMega clock<\/figcaption><\/figure>\n

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Web based simulation of version 2.0 of the clock<\/a><\/p>\n

Source code (C++) Arduino IDE<\/a><\/p>\n

Source code (version 1.9) – removed leading zero and number 7 tails. Added ability to turn seconds display off.<\/a><\/p>\n

Source code (version 2.0) – added 12 hour mode, date and temperature display. Optional remote control.<\/a><\/p>\n

Button library<\/a><\/p>\n

Bill of materials<\/a><\/p>\n

Addendum to schematic & BOM – the 330 ohm resistors should, ideally be 390 ohm instead as with some LED displays the seconds display may be dimmer. There’s about 3mA difference in segment current between the main digits and the seconds which is not noticeable on the displays I used as shown on the schematic. But to keep segment current within 1mA use 390 ohm resistors instead. Do not reduce the value of the current limiting resistors on the seconds displays to make them brighter as this would result in too much power dissipation through the resistors. Segment current will be approximately 16.5mA.\u00a0<\/span><\/p>\n\n

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