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This shield offers a quick way to add alphanumeric display capabilities to your Arduino project. It is based on the 14-segment 6-character LED display driven by two multiplexed MAX7221 drivers, through a method described in this application note .  US$ 26 - free shipping to North America The kit includes: PCB 2 x MAX7221 + 2 x 24-pin sockets 6-character 14-segment common cathode LED display 2 x 33k resistor 2 x 100nF capacitor machined header (as socket for the display) male header (for the shield) The board has a small prototyping area for adding project-specific parts, for example buttons and buzzer if you want to build an alarm clock (basic clock code for this shield here ). Assembled, showing the time (from wsduino ): or, displaying text: The shield uses Arduino pins D3, D4 and D5.

MAX6955  is an interesting LED driver chip. It is the primordial charlieplexing device, being the materialization of a technique invented by Charlie Allen of Maxim Integrated. Without understanding how charelieplexing works, it is actually counter-intuitive to wire multiple (up to 8) 16-segment displays to such a driver chip. Fortunately, Maxim has great documentation on how to do it. My experimenting actually started with MAX6954 . After many failed tries due to SPI issues (Maxim uses a special interpretation of the protocol, I read), I switched to MAX6955. MAX6955 is the I2C sibling of MAX6954 (which uses SPI). They both have identical LED driving abilities, only the microcontroller interface part of the chips differ. Once, both chips were available in DIP-40 package. Now, MAX6955 only comes in SSOP-36 (MAX6954 is still available in DIP-40). Luckily, the pin configurations for the two chips are compatible, which allows for easy swap. For this reason, I designed a breakout board...

There are many ways (*) to drive the 6-digit 14-segment common cathode display from Seeed Studio. This time I chose to multiplex two MAX7221 , a method described here  (but used for driving a bi-color 8x8 LED matrix). The code is based on LedControl library , which I extended to cover the definition and display of 14-segment characters (digits, upper case letters, and a few specials). Below is a relevant fragment of the code I added: /* * Segment names in the 14-segment (plus DP) display: * *     -     A *   |\|/|   F,I,J,K,B *    - -    G,H *   |/|\|   E,N,M,L,C *     -  .  D,P */ // my wiring: //            GFEDCBAx // 1st byte: B11111111 // //            NHJIKMLP // 2nd byte: B11111111 const static byte charTable14Seg[43][2] = {     {B01111110,B10001000},  // 0     {B00001100,B00001000},  // 1     {B1...

I saw Justin's recent post on Alpha Clock Five and I just couldn't resist not to try it myself too. Since I didn't have that clock, I thought of improvising one by making a 5-character display that would plug into my Wise Clock 4 board. The idea was easy, the implementation not so. After many hours of hand-wiring, this is how it looks like. The displays are 1" single digit alphanumeric  (common anode) from sparkfun, now retired. They came with non-functional dots, probably the reason they were less than $2 each. The spacing between the individual displays is forced by the protoboard. The 2 boards are connected through the pairs of 2x8 headers. All pins used by Alpha Clock 5 to drive the displays are wired to the unused header on the Wise Clock 4 board. Not to mention  that the software compilation and upload worked without any glitch (after downloading the very nice  DS1307RTC library ) The only regret is that this clock lacks seconds. One extra display would have a...

Update Sep 18, 2017:   Here is the latest revision of the PCB included in the kit. Update Oct 8, 2015 : The latest revision of the PCB (pictured here and here ) has hardware support for XBee (which also covers GPSBee, WiFiBee and BTBee). With this kit you build a clock like the ones shown in the photos below. Last one, courtesy of Nick, features an yellow/amber display. There are two buying options: 1. use or make your own enclosure  (US$47, free shipping to North America) 2. enclosure included ( Serpac A20 , transparent front panel, screws, back panel hand-drilled with 3 holes for buttons and rectangular opening for the USB connector )  (US$61, free shipping to North America) The kit includes the following electronic parts: main PCB display adapter PCB ATmega328 with 8MHz bootloader, programmed with a clock sketch + 28-pin socket 74HC595 shift register + 16-pin socket HDSP-2534 8-character alphanumeric display + 4 x 6-pin machined headers DS3231 + ...

I could have added a second bubble LED display to my "bubble clock" by connecting the anodes for the 4 new 7-segment digits to the only 4 pins left available: D0, D1, A6 and A7. Instead, I preferred to use the expensive ($8+) LED driver MAX7219 . Luckily, I got mine a long time ago as free sample from Maxim, and this was my chance to use it. As one can expect, the "double bubble" clock can display the seconds, plus the date and day of the week. Below are the 2 bubble clock versions side by side. Both are ProMini shields, so ProMinis get plugged on their backs. I designed them to stand by themselves with the electronics exposed and on the open, as shown in this post . I am not sure if this is a good idea, but designing (or finding) an enclosure seems even a bigger challenge. The sketch, included below, uses the LedControl library (communicates with MAX7219 through SPI). #include "LedControl.h" #include "Wire.h" #include "DS1307.h" #defi...

MikeM sent this photo he took of the guts of the revolutionary-at the-time Sinclair Black watch beside the Bubble clock shield . Mike also noticed odd behaviour of the clock shields (both bubble and OLED ) when powered from the 3.7V LiPo battery (as shown here ). After a while, the RTC returns bogus time. A quick check of the DS1307 datasheet (page 3) confirmed my suspicion: When 5V is applied within normal limits, the device is fully accessible and data can be written and read. When a 3V battery is connected to the device and VCC is below 1.25 x VBAT, reads and writes are inhibited. However, the timekeeping function continues unaffected by the lower input voltage. As VCC falls below VBAT the RAM and timekeeper are switched over to the external power supply (nominal 3.0V DC) at VBAT. Therefore, if one really wants the clock(s) powered from LiPo, a step-up converter must be used. Another solution is to replace the DS1307 with the (almost) pin-to-pin compatible DS1337 . This one does...

Update May 6, 2016: This kit is no longer offered until I get a new batch of QDSP-6064 displays (whose price seem to have jumped considerably). This clock was designed as a ProMini shield. It comes as a mostly-SMD kit, based on DS1307 with battery backup and the QDSP-6064 7-segment LED "bubble" display. The kit includes the following: PCB QDSP-6064 DS1307 SMD 32kHz crystal CR1220 coin battery battery holder 330 ohm resistor 0805 (8x) tactile switch SMD (2x) machined female pins The assembled clock can be fitted with a LiPo battery shield for ProMini, as shown in this post  (source code also provided there). The current draw (measured at 20mA with an unmodified ProMini) can be minimized by removing the 2 LEDs on the ProMini board, as well as dimming the 7-segment bubble display through software (SevSeg library). One other way of maximizing the LiPo battery life cycle is by waking the clock from sleep mode at the press of the "minutes" button (on D2). Schematic and ...

Updated Aug 30, 2014: A kit for this clock shield is now offered here . I am not particularly attracted by 7-segment LED displays, but I liked the HP bubble display that Sparkfun started selling recently. Like with the Nixie tubes, there aren't many things one can build with them, and my obvious choice was a clock. Being one of the smallest 7-segment LED displays out there, the clock had to be miniature as well. It took some thinking and planning to come to this final "design": This micro clock uses the Pro Mini sandwiched between the LiPo battery undershield and the display shield (that also includes the RTC), both DIY on protoboard. The LiPo undershield uses a cheap (less than $1 on ebay) USB charger board , which also provides the USB connector for power, since Pro Mini does not have one. The small 180mAh LiPo battery sits on top of the charger, but still allowing the 2 LEDs ("charging" and "charged") to be visible. There is also a switch for turn...