Connections

Ok, so I never got around to writing up the connections needed for Arduino Uno and my favourite 7 segment displays. I’ve had a few sets from this supplier and they’ve been a pleasure to deal with – very efficient, professional and courteous service. And a great product at a great price, what’s not to like?!

Some people have pointed out that you can get 7 segment digits much cheaper than this. Well, yes, but NO! If you want drive one of these (and you’re talking 12V for the feed) then you’d better factor in a shift register (Arduino soon runs out of pins), then you need a transistor to drive each digit (that’ll be 8 of those then) and a resistor for the base of each transistor (another 8). Don’t forget a resistor for each segment (Yup! 8 of those) and maybe a de-coupling cap for the shift register. That’s a lot of bits per digit. I like these because:

Job done!

Job done!

And they’ve added a 5V regulated supply – so you can power your Arduino from this. If you start to think about using all of those components (especially of the through hole variety) then the costs, the time to put it all together and the space required really start to add up. To my mind, this stuff is fantastic value – if I’m building a clock then I’m building a clock, all the other stuff just gets in the way.

Ok, how do we connect all of this up? One day, I’ll buy a proper camera but for now all I have is my phone…

All together now...

All together now…

Here are 4 digits, connected together and a socket added for a 12V feed.

LED Connections

LED Connections

So we have a purple wire on “S_IN” – this is the serial data in line and connects to “MOSI” (Pin 11) on the Arduino Uno SPI interface.

The green wire on “STB” connects to pin 8 on the Arduino Uno (it’s the pin I chose for “Chip Select”).

Yellow is “CLK” which goes to “SCK” (Pin 13) on the Uno.

Connect “GND” to, er, “GND” on the Uno and you’re nearly there.

One the Arduino has been programmed you can power it by connecting “VCC” to “5V” or “VIN” on the Uno – I prefer “VIN” as it just adds another layer of protection and keeps it away from the USB supply if you manage to connect both at once.

That’s really all there is to it.

Arduino Uno Connections

Arduino Uno Connections

I use the ShiftPWM library to drive the digits. My sketch is here – it’s setup for 4 digits and just cycles through 0 – 9 then “.” on each.

The result? Here you go…

All the fives

All the fives

That’s all there is to it. These things are really easy to drive – all the hard work has been done for you. If, like me, time to do stuff tends to be the problem then using these digits allows you to focus on what you want to do. You can’t beat that.

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