Saturday, August 30, 2014

ProMini clock shield with OLED display

Yet another ProMini clock shield kit, this time featuring a 128x64 I2C OLED display.

The kit can be purchased with or without the OLED display (I prefer you buy the OLED on your own, for example this excellent one from miker).

  US$30, includes OLED display, free shipping to North America

  US$16, OLED not included, free shipping to North America

The kit includes:
  • PCB
  • DS1307 SMD
  • 32kHz crystal
  • CR1220 coin battery
  • battery holder
  • optional: I2C 128x64 OLED display (blue or white)
  • tactile switch (2x)
  • resistor 10k (2x)
  • machined male pins

The PCB was designed to accommodate I2C OLED displays with the 4-pin header configured either as VCC-GND-SDA-SCL or as VCC-GND-SCL-SDA.

The OLED clock can also be powered from the same LiPo battery shield for ProMini, as used in the bubble clock. To minimize current consumption (beside disabling the ProMini on-board LEDs), the processor can be awaken from sleep at the push of the "hours" button (on D3).

Schematic and board layout are shown below.

The OLED clock could show the time in many different ways, including Pong mode (sketch adapted from miker), analog clock mode, digital clock mode (sample sketches to be provided soon).

ProMini clock shield with 7-segment bubble display

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.

   US$18, free shipping to North America

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 board layout are shown below.

Back in "business"

Just returned from my vacation in Paris. Hotel de Crillon was closed for renovations, Ritz had limited availability also due to renovation, so I had to settle for The Peninsula ;)

Here are a few impressions and observations, while still fresh.
  • taxis only take cash; ride from the airport to Paris center is about 60 euro and takes about 50 minutes;
  • the lowest cost Starbucks coffee is twice as expensive as here, at about $4.5 (3 euro), but still a lot cheaper than the "cafe creme" at Les Deux Magots or Cafe de Flore;
  • cheques are still used for grocery shopping (!);
  • the fixed air conditioning units (installed outside the windows) are probably not allowed, since they would really spoil the beauty of the buildings; posters are also forbidden, though I saw some "pixel art" placed high (that is, hard to remove) on some buildings;

  • one can actually live on and retire from a job as waiter or hotel concierge;
  • tipping in restaurants or for services is not a habit;
  • selling padlocks around famous places is big business;
  • Lacoste has a "lab" which also makes beautiful bicycles (this may be of interest to Justin :)
  • great Star Wars animatronics in DisneyLand Paris;

  • charging stations for electric cars;
  • and finally, a (probably expensive) clock :)

Thursday, July 17, 2014

New kit in store: simple clock with HDSP-2534 display

The centerpiece of this clock kit is the vintage-style 8-character display HDSP-2534 originally from HP, currently manufactured by Avago. The assembled clock looks like in the photo below. The dock, not included in the kit, is a miniB USB phone charger; it can be easily sourced from ebay, if you don't already have one. (You can even get a fancy one, e.g. custom-made exotic wood, on

The kit includes the following components:

  • PCB;
  • ATmega328P, with bootloader and fuses for 8MHz internal clock, and the sketch preloaded (also downloadable from here);
  • HDSP-2534 display;
  • 595 shift register;
  • DS1307 real time clock;
  • 32kHz crystal
  • CR1220 battery;
  • battery holder;
  • push buttons (x2);
  • capacitor 100nF (x3);
  • 10k resistor (x3);
  • 28-pin socket;
  • 16-pin socket;
  • 8-pin socket;
  • 6-pin machined female header (x4).

   $40, free shipping to North America

Note: The kit is currently out of stock. Please send me an email (my address is in the top right corner of the page) if you want one. I will put together only a small number of kits at this price, since the display itself is sold by digikey for about $40.

Schematic and board layout are shown below. Preliminary Eagle files can be found here.

The kit is super easy to assemble. It is really impossible to misplace components on the board.
Still, here is some advice:
  • pay attention to the orientation of each of the three integrated circuits, when you insert them in their respective sockets;
  • before soldering the battery holder, put some solder on the big center pad;
  • avoid solder bridges between the USB miniB connector's terminals by wetting their pads (on the bottom side) with a flux pen;
  • it is recommended, for aesthetic purpose, not to solder the FTDI connector to the board; if you need to upgrade the existing software (download from here), you can just hold the 6-pin make header tightly in place while uploading the sketch;

Thursday, July 10, 2014

bGeigie Nano PCB remixed

As I pointed out in my review on Safecast bGeigie Nano kit, the size of the current software already reached the limit of processor's program memory of 30KB or so. From this point on, it is difficult (if not impossible) to add new code features, and that may require drastic code optimization or even disabling existing features.

I thought that the easiest solution to keep this project up-to-date is by upgrading the processor, by entirely replacing the Fio board with an ATmega 644P plus a few extra components (e.g. LiPo charger). This makes the kit a bit more challenging to build, since it requires soldering SMD components, but could also save a few bucks. The device is still Arduino-compatible and programmable, like to Fio, using the FTDI breakout.

Updated Jul 11, 2014: As Rob suggested, I added the XBee module as well. New Eagle files are here.
This is how the bGeigie Nano Plus PCB looks now. (I also added an option for the Fastrax UP501 module, a bit cheaper then the Ultimate GPS breakout, but still a great GPS module (if you can find it on ebay or other sellers)).

The Eagle files for the upgraded bGeigie Nano can be found here.
On the board, the positioning of the modules, switches, headers etc. is the same (except for the Fio, which is now gone).

A few more points:
  • The LiPo charger follows Fio's schematic, using the exact same components.
  • The ATmega644P processor will require burning the bootloader (board has ICSP header).
  • To compile and upload sketches, the Sanguino core files need to be added to the Arduino IDE (as detailed in this post).
  • ATmega1284P, with double the program memory, could be used instead of the 644P, since it has the exact same footprint (and it is pin compatible).

Unfortunately I am short on cash these days, so I hope someone could order the PCB with oshpark (the set of 3 original PCBs was $52 when I ordered them a while ago) and prove the design. I could help with the IDE setup and probably with some software development as well (the first thing that comes to mind is using the whole 128x64 OLED screen, and not just half).

As always, any feedback is appreciated.