Combine three inexpensive LED matrix display panels, an Ardweeny microcontroller and a standard PS/2 computer keyboard into your own go-anywhere, instantly updatable 768-pixel digital message board.
The code can hold up to six lines of text with a maximum of 100 characters each. Pressing a key on the keyboard gets you to input mode. Use the up and down arrow keys to select which line to edit. ENTER puts the system back into output mode. When in output mode, each line of text will display for 1 second (you can set this in the sketch), or if the line is longer than 16 characters, it will scroll across the display before moving onto the next line.
Send some text messages:
The uses for this contraption are many. Plug the keyboard in and enjoy putting your wittiest “wiseclacks” on it in the safety of your home, shop, or office, or use the battery option to take it into the wide world. We like to leave the keyboard accessible so that passers by can add a riposte or two to the dialogue, but if monologue is more your thing you can always take it elsewhere. Here’s another idea: drill a broomstick-sized hole in the bottom of the frame and add a removable handle so you can wander the streets digitally promoting your geekified political leanings. Score keeping at sports events, birthday greetings, advertising your wares at a farmers market, beaming cryptic messages to your neighbours across the street – the possibilities are endless!
Step 1: Materials and tools
Frame wood (A): 4′ of 1×4 (nominal dimensions) or similar sized board, or double that length of 3/4” x 1 5/8” stock
Eight wood screws (B): #8, 1 ¼” long
Three 8×32 dot matrix LED displays from Sure Electronics (C). $12.90 ea. http://www.sureelectronics.net/goods.php?id=1118
DC power jack to match your adapter (E). Here is a standard 2.1mm one from Sparkfun for $1.25 http://www.sparkfun.com/products/119
SPDT (on-off-on) power switch (D). Digikey part#: 450-1527-ND
PS/2 port from an old computer motherboard (F) (ask a local computer shop and they will likely give you a defunct motherboard for free).
A 21” x 4” piece of 1/8” or 1/4” Lexan or Plexiglass (G) (try your local auto glass shop). I used this to make a clear back for the frame, so that you could still see the stuff going on inside. Wood paneling or plastic would work too.
2 AA battery holder (I) http://www.sparkfun.com/products/551
4 AA battery holder in a long, flat configuration (H) http://www.sparkfun.com/products/9547
A few feet of 22 AWG stranded wire (J).
Flexible breadboard jumpers (K). $6.00 at Solarbotics: http://www.solarbotics.com/products/21035/
You can use solid 22 AWG wire for this, but purpose-built breadboard jumpers are more flexible and much easier to use – well worth the expense.
Electrical tape or heat shrink tubing (L).
Mini self-adhesive breadboard (M): $3.95 at Sparkfun: http://www.sparkfun.com/products/8802 or $4.00 at MakerShed: http://www.makershed.com/ProductDetails.asp?ProductCode=MKKN1
Ardweeny microcontroller (N), from MakerShed ($9.95) http://www.makershed.com/ProductDetails.asp?ProductCode=MKSB012 or Solarbotics ($9.99) http://www.solarbotics.com/products/kardw/
The Ardweeny is an Arduino-compatible microcontroller with a tiny footprint — just the size of the Atmega chip itself. This (and its equally diminutive cost) make it a great choice for breadboard-based projects that need to fit into small places. Unlike the Arduino, Ardweenies requires an external USB/serial programming adapter. They’re pretty cheap too though: $15 from MakerShed ( http://www.makershed.com/FTDI_Friend_v1_0_p/mkad22.htm ) or Sparkfun ( http://www.sparkfun.com/products/9716 )
5v regulator (O). 7805 series regulators are cheap and plentiful ($0.29 from MakerShed: http://www.makershed.com/ProductDetails.asp?ProductCode=JM51263) but a low dropout model like the lm2937 will give you more run time on batteries, especially if you’re using lower-voltage NiMH AAs ($1.50 at Solarbotics: http://www.solarbotics.com/products/lm2937/)
0.1 μF (104) ceramic capacitor (P)
10 μF electrolytic capacitor (Q)
Six small pan head screws (R) (for holding on the back cover)
9 – 12v AC/DC adaptor (S). The best place I’ve found to get adaptors is a Salvation Army thrift store. They usually have a large selection for about $1 a piece. If you haven’t got a thrift store handy, there’s one for $5.95 at Sparkfun (http://www.sparkfun.com/products/298) or $6.50 at MakerShed (http://www.makershed.com/ProductDetails.asp?ProductCode=MKSF3)
Standard PS/2 computer keyboard (T), or USB keyboard with PS/2 adapter.
For reduced hassle and time input, a kit containing the collected materials to build this project can be purchased at the Maker Shed Store: http://www.makershed.com/PS_2_You_Parts_Kit_p/msps2u.htm
Hand saw or chop saw
Table saw (optional)
Drill and bits
Soldering iron and solder
Pliers and cutters
FTDI serial programmer (available from sparkfun for $14.95 — http://www.sparkfun.com/products/9716)
Step 2: Cut the frame boards
There are several ways the frame could be made. I had a wood shop at my disposal, so I made something like an extra-deep picture frame, with mitred corners and a slot cut in the long sides to hold the display panels. The shape and style of the frame is not crucial, so let your creativity (and materials) have a say in the design.
Cut the 1×4 in half lengthwise to make two strips that are about 3/4” x 1 3/4” (a typical “1×4” is actually around 3/4” x 3 1/2”).
Use a chop saw or hand saw to cut a 45° angle on one end of each piece, oriented so the cut goes diagonally across the narrow surface of the board. From the inward side of the angle cut, measure 18 1/4” and make another 45° angle cut. Both cuts should angle outward from the the measured length. Repeat on the second board. These will be the two long sides of the frame.
Step 3: Measure display panel width
Line the two boards up beside each other on a flat surface with their narrow edges up. Place one of the display panels face down between the boards, so that the flanges on the panel rest on the boards, with the protruding LED matrix between them. Make sure the boards are snug up against the sides of the LED matrix. Measure between the outside edges of the boards. This will be the length of the end pieces of the frame.
Mark the distance you measured above in from the long end of the mitre cut on each of the remaining boards. In this case both mitres should go in from the measured length, which will be the longest dimension of each piece. Cut one of these. Mark the other, but don’t cut it yet.
Step 4: Measure and cut slot for IO ports
Line up your DC jack, PS/2 port and power switch atop the edge of the uncut piece you’ve just marked. Mark out a notch in the edge of the board just big enough for them to all fit into next to each other.
With a chop saw or hand saw cut the two edges of the notch. Make a few cuts to the correct depth in the middle of the notch, then chisel out the rest of the wood and smooth the bottom of the notch. Try fitting the ports and switch into the notch. They should slide in easily, but without extra space.
Step 5: Cut the second display panel notch
Cut the second, notched end piece as marked in step 3.
Set the blade of your table saw to a depth of 5/16” (the size of the flanges on the display panels). Cut a notch lengthwise down the inside of each of the long frame pieces, ¼ inch in from the edge. Use a narrow kerf blade if possible. This notch should match the flanges on the display panels so that the panels will slide into the slot and be roughly flush with the front of the frame.
Step 6: Assemble the frame
Slide all three display panels onto the slots, making sure they all have the same side up (check the writing on the back of the panels to confirm this). Fit the frame ends and, holding the frame pieces in place, drill pilot holes and counter sinks for the screws which hold the frame together. It may be helpful to put the screws in to keep the frame together as you go. Ensure that your counter sinks are deep enough and don’t over tighten the screws to avoid splitting the frame pieces. If you’d like, add some glue to the notched end of the frame for extra strength, but leave the other end unglued if you’d like to be able to get the display panels out.
The frame is now finished!
Note: If you don’t have access to a shop and or table saw, there are other ways the frame can be made. One way is as follows. Cut two 1×2 boards (really 1 1/2”x 3/4”) to 18 1/4”, and two shorter lengths of 1×2 to fit on the ends. Then, rather than notching for the display flanges, use the pre-drilled holes in the flanges and screw them onto the front of the frame.
Step 7: Add the Back Cover
Place the assembled frame on top of the plexiglass or Lexan sheet. Using a screw or other primitive object, scratch a mark around the edge of the frame.
Cut out the backing with a hand saw, table saw or the cutting implement of your choice. Line up the cut piece on the back of the frame and drill six pilot holes through the backing material and into the back of the frame itself. It is now ready to be closed up once all the electronics are in place and functioning.