Introduction: ATtiny85 Clock

Picture of 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

Picture of 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

Picture of 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

Picture of 4-digit 7-segment Display

Step 4: ATtiny85

Picture of ATtiny85

Step 5: Code

Picture of Code


About This Instructable




Bio: I'm an electronics hobbyist.
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