Arduino Forum

Using Arduino => LEDs and Multiplexing => Topic started by: Frax23 on Jan 11, 2019, 12:04 pm

Title: Connecting 3 digits 7 segments 28 pins to IC 7447 to Arduino Uno
Post by: Frax23 on Jan 11, 2019, 12:04 pm
This is the first time I'm using an Arduino. I have a 3 digit 7 segments display with 28 pins, an IC 7447, and I am using an Arduino Uno. I just wanted to know how do I cable the 7 segments to the IC and the code I need to upload to the Arduino to create a simple counter.
Title: Re: Connecting 3 digits 7 segments 28 pins to IC 7447 to Arduino Uno
Post by: Grumpy_Mike on Jan 11, 2019, 04:47 pm
http://wherethewildoneroams.co/7447-bcd-to-7-segment-display-49/ (http://wherethewildoneroams.co/7447-bcd-to-7-segment-display-49/)

For a common anode seven segment display. Is that what you have got?
Title: Re: Connecting 3 digits 7 segments 28 pins to IC 7447 to Arduino Uno
Post by: Paul__B on Jan 11, 2019, 11:48 pm
I think you need to start by detailing - generally by giving Web links - exactly what display you have.  28 pins sounds quite inconsistent with a 3 digit display.

The 7447 is essentially obsolete and probably of little use here, but only when we know about the display can we suggest anything at all.
Title: Re: Connecting 3 digits 7 segments 28 pins to IC 7447 to Arduino Uno
Post by: Frax23 on Jan 12, 2019, 03:53 am
This is the 3 digits 7 segments display I have. It is actually 27 pin
Title: Re: Connecting 3 digits 7 segments 28 pins to IC 7447 to Arduino Uno
Post by: PaulRB on Jan 12, 2019, 10:13 am
I suggest you start by driving just one digit. Connect one of the common anodes to 5V. Connect the cathodes for that digit to the 7447 outputs using 7 series resistors, e.g. 220R. Connect the 4 BCD inputs of the 7447 to 4 Arduino digital pins (don't use 0 or 1). Write a simple sketch to count from 0 to 9.

To drive the other two digits, probably the simplest option for you is to use 2 more 7447 ics. Another more interesting option would be to multiplex the display. For this, you would only need a 7447 chip but also 3 pnp transistors, e.g. bc327.

There are many more ways to drive this display. What other chips and components do you have to hand?
Title: Re: Connecting 3 digits 7 segments 28 pins to IC 7447 to Arduino Uno
Post by: Grumpy_Mike on Jan 12, 2019, 10:18 am
For that display you need to use three 7447 chips one for each digit along with the current limiting resistor for each segment.

Each 7447 chip then needs four outputs from the Arduino connected to it, so a total of 12 outputs. Each group of four outputs determine the digit that is shown on that display.

To help you with your software you need to use arrays, as shown here:- http://www.thebox.myzen.co.uk/Tutorial/Arrays.html (http://www.thebox.myzen.co.uk/Tutorial/Arrays.html)

An example of multiplexing is shown here:-

(https://forum.arduino.cc/index.php?action=dlattach;topic=590158.0;attach=289717)

Of course you don't need the fourth display but the circuit is the same. All the same segments on each display need to be connected together.
Title: Re: Connecting 3 digits 7 segments 28 pins to IC 7447 to Arduino Uno
Post by: Frax23 on Jan 12, 2019, 02:25 pm
I suggest you start by driving just one digit. Connect one of the common anodes to 5V. Connect the cathodes for that digit to the 7447 outputs using 7 series resistors, e.g. 220R. Connect the 4 BCD inputs of the 7447 to 4 Arduino digital pins (don't use 0 or 1). Write a simple sketch to count from 0 to 9.

To drive the other two digits, probably the simplest option for you is to use 2 more 7447 ics. Another more interesting option would be to multiplex the display. For this, you would only need a 7447 chip but also 3 pnp transistors, e.g. bc327.

There are many more ways to drive this display. What other chips and components do you have to hand?
That's all I have, but I'll try your suggestions. Thank you!