Here it is in action! https://raw.githubusercontent.com/elgwhoppo/LANPartySign/master/images/xIRKag8QQ-qkcFby.mp4

Hardware

Raspberry Pi

We used a Raspberry Pi 3, but any Raspberry Pi with at least 14 available GPIO pins should do.

Aluminum street sign

http://www.roadtrafficsigns.com/Custom-Metal-Sign/Custom-Metal-Sign-24x18/SKU-K-3409-BK.aspx

The text used to create “YOUR SPEED” with sufficient space:

YOUR
SPEED
 
 
 
 

Press [Enter] four times after “SPEED” to create some space.

LED panels

Six 4” common anode LED panels, three in red, and three in green were glued together using JB Weld. It’s not very pretty on the back, but no one sees the rear of the panels anyway. I used a wet paper towel to wipe up the excess that oozed out the front.

These are the panels we used:

http://www.ebay.com/itm/182018966801

http://www.ebay.com/itm/252168875198

Power supply

A 12V/2A power adapter is sufficient to provide power to the RPi and drive the LED’s. This isn’t terribly special. This is the same type of wallwart-style power supply that comes with routers and cable modems.

https://www.amazon.com/gp/product/B0194B7WSI/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

The Raspberry Pi is also draws from the same power adapter via a cheap step-down buck converter. This is the one we used.

https://www.amazon.com/gp/product/B008BHB4L8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

LED driver board

Source IC

A UDN2984A source driver is required as the RPi’s GPIO outputs neither source enough voltage (3.3V max) or current (~30mA total) to drive the large LED panels.

Sink IC

A ULN2003AN Darlington array is required as the RPi’s GPIO can’t sink the return current without emitting smoke. A 2N7000 FET is used to drive one of the cathodes because the Darlington array I selected only had 7 pins and I needed 8.

Resistors

Current limiting resistors are required to keep the LED panels from burning up, and to keep the brightness between the two types of panels uniform. The segments that form each digit require different values from the decimal point as the decimal point has less LED’s inside.

The green segments used 110ohm resistors and red segments used 150ohm resistors. The green decimal point used a 4000ohm resistor and the red decimal point used a 800ohm resistor.

You may change the resistor values to your liking if you’d like it brighter or darker. We chose higher values since the sign would be used in a dimly-lit room (i.e. a LAN party). For a brighter sign, use a lower value. I wouldn’t suggest going lower than 60ohm for the digits and 250ohm for the decimal point.

Connections to the Raspberry Pi

Six GPIO’s (GPIO4, 17, 18, 27, 22, and 26) are used to bring the input side of the source driver high, which allows 12V to flow out the output side into the anode of each LED panel, which activates a digit.

Eight GPIO’s (GPIO24, 22, 29, 31, 32, 33, 35, 36) are used to bring the input side of the Darlington array high which grounds out the appropriate cathode. This activates a segment (or the decimal point).

Pins 2 and 4 power the Raspberry Pi through the step-down buck converter.

Wiring and connectors

A small length of 18GA wiring and barrel connectors are used to connect the LED driver board to the power supply.

https://www.amazon.com/gp/product/B0154MAECC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B01G6EAY0E/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

The LED panels used CAT5e cabling with RJ45 crimped on the ends. They were connected to RJ45 jacks and breakout boards from Sparkfun. Three were used in total. One for the anode bus, one for the green cathode bus, and one for the red cathode bus. We could’ve consolidated the cathode buses, but I was afraid I wouldn’t have room for current limiting resistors behind the panels. The current limiting resistors are on the same board with the IC’s which required two individual CAT5e cathode busses.

https://www.sparkfun.com/products/643

https://www.sparkfun.com/products/716

A 40-pin IDE cable was sacrificed to make the connection between the LED driver board and the Raspberry Pi.

Some protoboard was used to make soldering each panel to the bus easier, but I probably could’ve done with out them.

https://www.amazon.com/gp/product/B019Q14GRQ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Enclosures

The Raspberry Pi is housed in a ABS plastic case that allowed access to the 40-pin connector.

https://www.amazon.com/gp/product/B00MQWQT0A/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

The LED driver board, due to the strange size of the protoboard I used is housed in a 7.5” x 4.3” Hammond case.

https://www.amazon.com/gp/product/B0002BSRIO/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Fit and finish

A piece of tinted acrylic was glued to the front of the LED panels to give it a nice slick look. Unfortunately it's very reflective and impossible to photograph without seeing a reflection of someone or something :(

https://www.amazon.com/gp/product/B01A1C16TK/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

The Mb/s and ms units were printed on my laser printer using the same font used by the US Federal Highway Administration (Highway Gothic), laminated, and taped to the front of the sign because I ran out of time. However, more permanent unit labels printed on a vinyl printer will replace them.

https://github.com/elgwhoppo/LANPartySign/blob/master/units.eps

Four pairs of rare earth magnets keep the LED panel secured to the sign. Four magnets are adhered to the set of LED panels with JB Weld. I love JB Weld.

The enclosure for the Raspberry Pi and LED driver board are double-sided-taped to the back of the aluminum sign.

Software

We used on rebuild:

• Raspberry Pi OS (32-bit)
• Python 3.9.2 that came with updated Rasberry Pi OS
• Screen for the watchdog process - sudo apt install screen
• https://pypi.org/project/pysnmp/ - sudo pip3 install pysnmp
• pip3 install pyasn1==0.4.8 (had to downgrade for compatability)
• The RPi.GPIO library. No install required with python 3.9.2.

The Python Scripts

The Python script does all the heavy lifting of the sign and runs on the Raspberry Pi. It creates the precisely-timed pulses required for multiplexing the digits, as well as gathering the data displayed on the sign.

This script has been completely reworked as of October 2023, to leverage multi-processing and pipes for better efficiency. Error handling via a Watchdog service and better exception catching are also used. Python reaches out using three scripts:

• sign.py <--Parent
• ping.py <--Child
• snmp.py <--Child

Calling sign.py will after a boot up cycle, call ping and snmp, getting the data accordingly.

tl;dr “what do i need to buy?”

Some of the parts may need to change based on your needs of the sign as well as if you don’t want to repeat the same poor design decisions I made.

1x Aluminum street sign

• http://www.roadtrafficsigns.com/Custom-Metal-Sign/Custom-Metal-Sign-24x18/SKU-K-3409-BK.aspx 

6x LED panels

• 3x http://www.ebay.com/itm/182018966801
• 3x http://www.ebay.com/itm/252168875198

Power supplies

• 12V/2A power supply https://www.amazon.com/gp/product/B0194B7WSI/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
• step-down buck converter https://www.amazon.com/gp/product/B008BHB4L8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

LED driver board

• 1x large protoboard
• 6x small protoboard https://www.amazon.com/gp/product/B019Q14GRQ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
• 1x UDN2984A
• 1x 18-pin socket for UDN2984A
• 1x ULN2003AN
• 1x 16-pin socket for ULN2008AN
• 1x 2N7000 MOSFET
• 7x 110ohm resistors
• 7x 150ohm resistors
• 1x 4000ohm resistor
• 1x 800ohm resistor
• 3x RJ45 crimps
• 3x Sparkfun RJ45 jacks https://www.sparkfun.com/products/643
• 3x Sparkfun RJ45 breakout boards https://www.sparkfun.com/products/716

Wiring

• 1x a bunch of scrap CAT5 to salvage solid wiring from
• 1x some scrap 18GA wire https://www.amazon.com/gp/product/B0154MAECC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
• 1x 40pin IDE cable
• 1x pair of male and female barrel connectors https://www.amazon.com/gp/product/B01G6EAY0E/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Raspberry Pi 3

• Raspberry Pi 3 single board computer https://www.raspberrypi.com/products/raspberry-pi-3-model-b-plus/
• 8GB SD card https://www.amazon.com/gp/product/B000WH6H1M/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Enclosures

• 1x Hammond case https://www.amazon.com/gp/product/B0002BSRIO/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
• 1x Raspberry Pi case with GPIO header access https://www.amazon.com/gp/product/B00MQWQT0A/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Fit and finish

• 1x 3M double-sided tape
• 1x JB Weld
• 1x tinted acrylic https://www.amazon.com/gp/product/B01A1C16TK/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Things I would do differently

• Prototyp