Making a clock

30 Dec 2025 · Proof of Concept · ESP32 · 7 Segment Display · NTP

A proof of concept

I was watching something on YT the other day and they had a Masterclock CLDNTD12 Digital Analogue Clock onscreen. I'm surrounded by accurate clocks, my phone gets the time from my mobile network provider, my PC displays the time from NTP, my watch displays time from GPS, I've got a raspberry pi hooked up to a GPS antenna that acts as a Stratum-1 NTP server. So I know what time it is. As soon as I saw the Masterclock I was hooked by it's simple and interesting design. I needed one in my life.

So I did a little googling. I'll save you looking, you're talking well over a grand if you want one. I'm not yet at a stage in my life where I can justify £1,200+ for a clock in my room! But I'm not one who gives up easily...

v0.1

I pulled down a couple of electronics bits boxes and had a root about, I couldn't find what I was looking for so I pointed my browser at ebay and a couple of days later I had what I needed for v0.1 (Proof of Concept).

ESP32-S3 Microcontroller
8 Digits of 7 Segment Display on a Max7219 Backboard
An RTC Module

The RTC is for backup if my LAN is ever down, the pi provides the actual time.

These things are amazing, so versatile, relatively powerful and only a fiver each! Amazing.

I hooked up the 7 segment displays to the ESP with some jumper wires and wrote a little sketch in Arduino IDE. It interfaces with the MAX7219 which controls the displays, connects to the IoT WiFi and grabs the time, then shows the time on the displays and turns the RSSI into a signal strength, no bars = offline, 1 bar = poor signal, 2 bars = good signal, 3 bars = excellent signal.

It draws 40-42 mA under normal use, the WiFi turns on, grabs the time and turns off every 3 hours, the WiFi is in sleep for the rest of the time allowing the RSSI bars to remain "on screen" and the CPU is down to 80Mhz... my first PC was a 386SX @16Mhz, so 80Mhz is fine for a clock!

The PoC clock is double sided tape stuck to the bottom of my main monitor, classy. Here's some footage of the clock, the flicker is because of the frame rate, it's not noticable in real life.

V0.2

I've added a 220µF capacitor across the VCC & GND pins to stabalise the 5v supply, the tenths counter makes the draw for the LED segments very spiky and without it the display would every now and again go dim or display random segments. A chonky capacitor has solved this and it's worked glitch free for a week or so now.

I got some feedback from Mitch about it not being in any sort of case, so yesterday I unplugged it, measured it, and 3D printed a little case for it. The blocks ensure that the face of the displays sit flush with the front of the case. The display cutout is pretty tight, so there's no danger of it falling out during any particulally intense what time is it checks.

If you have one of these fleabay 8 digit display modules and want to print a simple case to allow you to neatly stick it (still with double stick tape) to the bottom of your monitor the file is here

Installed. Sure I could fill it, sand it & spray it, but then it'd be finished, and I don't do finished!

v1.0

The plan for the v1.0 clock is to get 4 bigger (40-50mm) red 7 segments for the HH & MM markers, with a couple of red dots as colons seperating them. Then 2 15mm (ish) blue or green 7 segments for SS and 2 10mm (ish) blue or green for the 10th of seconds which will sit under the HH MM segments. Round the outside there will be 60 neopixels 1 will come on every second with every 5th one lighting up a different colour. A little OLED screen up top to show the day of the week and IP Address. 6 rectangle LEDs 1, 2, 3 for a WiFi strength indicator.

It'll all sit in a 3D printed square case with a circular smoked perspex cover for the display. I'll power it with a USB PSU. I'll be ordering the 7 segments tonight, and I'll put part 2 up here when I've built it. Until then...