Raspberry Pi 2 DIY LED LAN device counter

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3 Step 3: Cut out a piece of perfboard and start soldering

5 Step 5: Download and install firmware for Arduino IDE to be able to compile

Do you know how many devices are on your local network? That is what we where wondering at our hackerspace HackBergen.

Yes, there are available programs and Apps to scan your network, but we can also scan with the Raspberry Pi (RPi) and show the result on a set of 7-segment displays.

These look cool, retro, are cheap and can be seen from a distance for you to have a general idea of how many devices are currently operating on your local network in these IoT times.

This build uses 3 modules of 7-segment common Anode LED displays that are controlled by an Atmega328. We use 3 because normal home LANs are C nets with a maximum of 256 devices and I had 3 of these nice 7-segment displays lying around. 🙂

The (AVR Atmega) 328 is loaded with the Arduino bootloader on an Arduino Uno 28pin AVR and then programmed with the Arduino 1.0.1 IDE through the Raspberry Pi on board serial port. The software is the firmware that Sparkfun uses on their serial backpack, but we have to modify a couple of lines since they use a 32 pin SMD 328 instead of the normal 28pin DIP version from the UNO.

By using an 328 for this, we do not need more than the serial port’s 2 pins to control the display, and all multiplexing and buffering is done by the 328. No need for a program to do the multiplexing of the 7-seg displays and be problematic with irregular timing. We can also use the built in i2c bus to control it if we want to.

Using the serial port makes it very easy to display 7-seg chars on the display, remaining there until we update it again. This is great for piping information from scripts, and we do not need a program running constantly as a daemon.

You could of course buy a single 4 digit display from SparkFun ready-made and connect it to your Linux box or your RPi, losing all the DIY fun. That is totally up to you. 🙂

Step 1: What hardware do we need?

Soldering Iron with de-soldering gadgets
Multimeter with continuity tester
Wire
Perfboard
Lupe or magnifying glass to check the soldering
Sharp or X-acto knife
Arduino Uno
3 pcs common Anode 7-segment display
Atmega AVR 328 DIP 28pin IC
Sockets
- These are optional, but makes it easier to sneak wires behind the ICs
Resistors.
- I used a 8 DIP 180ohm network for the segments as I find these convenient for things like this.
- 220 ohm for driving the base of the transistors
NPN transistors. We used the 2n2222.
Raspberry Pi B, B+ or 2.
Ribbon cable – 40 pins or 26. We could use 10pin but that might ruin the RPis header.
Header connector
Breadboards. Optional as you can just reflash the bootloader on the UNO, but we did use the UNO to program the 328 on a breadboard. It is only done once.

Step 2:

What is connected to the 328 on our build:

10K resistor +3.3V / Switch GND
RPi TXD pin 8
RPi RXD pin 10
LED dp -> pin 8 DIP resistor
LED seg 3 transistor base resistor
NC
+3.3V
GND
NC
NC
LED g -> pin 7 DIP resistor
LED c -> pin 3 DIP resistor
LED f -> pin 6 DIP resistor
LED a -> pin 1 DIP resistor
LED e -> pin 5 DIP resistor
NC
NC
NC
NC
+3.3V
+3.3V
GND
LED b -> pin 2 DIP resistor
LED d -> pin 4 DIP resistor
LED seg 1 transistor base resistor
LED seg 2 transistor base resistor
RPi SCL pin 5 (optional)
RPi SDA pin 3 (optional)

Original Schematics this is based on: Original 32 pin AVR schematics

Step 3: Cut out a piece of perfboard and start soldering

Decide on a size you want by placing your components on the perfboard and cut it out with a knife or saw.

I have a Olfa plastic cutter I really love for things like this, but a normal sharp knife works fine.

Step 4: Install 328 bootloade

There are a lot of great guides on how to program your Atmega 328 for simple use without external crystal 8Mhz use:

http://www.arduino.cc/en/Tutorial/ArduinoToBreadboard

Install Arduino IDE on the RPi so we can burn bootloader with the UNO:

sudo apt-get install arduino (This installs arduino 1.0.1)

Install 8Mhz breadboard arduino ref: http://www.arduino.cc/en/Tutorial/ArduinoToBreadb…

mkdir -p sketchbook/hardware

cd sketchbook/hardware

unzip /home/pi/Breadboard1-0-x.zip
arduino
- check for and select tools->board-> ATmega328 on a breadboard (8 MHz internal clock)

Make Link to serialport for arduino to discover after reboot
- sudo nano /etc/init.d/link_serial
  - #!/bin/bash
  - ln -s /dev/ttyAMA0 /dev/ttyS1
sudo chmod 755 /etc/init.d/link_serial
sudo update-rc.d link_serial defaults
sudo service link_serial start
check serial port link, to see if it exists
- ls -l /dev/ttyS1
run arduino IDE
- select tools->board->ATmega328 on a breadboard (8 MHz internal clock)
- Select tools->serial port->/dev/ttyS1
- Select tools->Burn Bootloader
- remember to push the reset button on your new board when compiling, right before upload
- You get “Done uploading” when OK or “problem uploading to board” if you wait too long. Just try again until you get it.