ATtiny85 Clock

About: I'm an electronics hobbyist.

Intro: ATtiny85 Clock

Because I use a lot of tutorials online, I figured I should give something back. So this is my first electronics tutorial, or any for that matter. I should note that I'm not a native English speaker So when I make a mistake or you think something should be a little different, I like to hear it.

In this tutorial I will be building an electronics clock, based on the ATtiny85. Which uses a max7219 to drive the 4-digit 7-segment display and an DS3231 as a Real Time Clock. It is part of a bigger project, it I thought I should start here.

Step 1: Parts

Needed for this project are the following parts:

Power circuit:

  • 1 x LM7805
  • 1 x Electrolytic capacitor 100uF
  • 1 x Electrolytic capacitor 10uF
  • 1 x Ceramic capacitor 100nF
  • 1 x 9 V battery plug
  • 1 x 9 V battery
  • (optional) 1 x led
  • (optional) 1 x resistor 220ohm


  • 1 x 4-digit 7-segment display (12 pins, common cathode)
  • 1 x max7219 led driver
  • 1 x Electrolytic capacitor 10uF
  • 1 x Ceramic capacitor 100nF
  • 1 x Resistor 40kohm
  • 1 x ATtiny85
  • 1 x Resistor 10kohm
  • 2 x Resistor 4.7kohm
  • 1 x Button
  • 1 x DS3231
  • lots and lots of jumpers

Step 2: 5V Power Supply

This part is optional, if you connect your Arduino power and ground pin.

All the electronics in this instructable work on 5vdc, so we need a 5vdc power supply. Because this circuit will eventually be built into a real clock, I can't use my Arduino power pins. So with a LM785 power regulator and some capacitors I created my own 9v battery to 5v circuit. The circuit in the picture is the one I used. Normally you calculate the capacitor values, but at this moment this is a little over my head.

All the ground pins are connected together, to create one common ground. The battery+ is connected to the 100uF capacitor+ to create a buffer. The battery+ is also connected the pin one on the LM7805. On pin 3 of the LM7805 the 100nF capacitor is connected to smooth out the incoming voltage from HF signals. The 10uF capacitor+ is also connected to pin 3 of the LM7805 to create a buffer. Between pin 2 and 3 of the LM7805 is now a 5vdc circuit.

Optionally a led can be connected in pair with a resistor, to see when the power is working.

Step 3: 4-digit 7-segment Display

Step 4: ATtiny85

Step 5: Code



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