Tabletop Stopwatch

This is a nice gadget I made for my son.

It is a tabletop Stopwatch, which displays seconds and minutes, with a simple start/stop button and reset button.

Hardware :

Plastic box

7 segments display

Max 7219 (to drive the 7 segments display)

Arduino Nano

LM 7805 (to make 5V power supply)

1 condo and resistor for the MAX7219

1 epoxy board

4 nylon screws

2 push buttons

1 switch

1 power plug

And of course, soldering iron, tools, wire...

1. The epoxy board is cut to fit right into the box top.
2. The electronic setup is simple. I added a diagram to make it more understandable.

• The MAX7219 has full of litterature on this site and internet to manage wiring
• The LM7805 is used to make 5V out of a 9 V or 12 V power supply. /!\ I didn't include a protection diode.
• Tricky part : my display has common cathode. As the MAX7219 is meant for common anode, I had to wire it the other way round and it make the use within the code a bit more tricky. The code contains a conversion table to map segments and digits. It certainly must be adjusted with your own wiring.

The code is available here :http://blog.ouiaremakers.com/wp-content/uploads/fo... (sorry for the mix between french and english within the code)

There you go, enjoy...