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I finally finished assembling, after more than a year, my bGeigie Nano . At over $400, this was by far the most expensive Arduino project I have built to date. The feature-rich open-source Geiger counter is offered as a kit by Medcom for the price of $450 (of which, $75 is donated to Safecast organization ). I stubbornly insisted on sourcing the parts on my own, to save a few bucks and to get a closer look at the process. Let me tell you: this may be the only kit out there where the components bought individually are as expensive as the kit itself! Obviously, this kit was not designed to make a profit. Here is a price breakdown (for non-believers): - PCB (OSHPark) - $17 (3 for $52) - Pelican 1010 box (store) - $13 - Arduino Fio  - $25 - GPS module - $40 - OpenLog - $25 - OLED display - $25 - laser-cut plates - $25 - sensor LND7317 - $150 - iRover HV supply - $35 - LiPo battery - $10 - SD card - $10 - other electronic components - $5 - hardware (standoffs, screws etc) - $5 - shippin

This single-digit Nixie clock is built on a piece of prototype board, as a ProMini shield, similar to two previous miniature clocks, the single-digit numitron clock and the 7-segment bubble clock . The shield holds the Nixie board and the high-voltage power source (both from Taylor Electronics). It also has a couple of buttons to set up the time and 4 LEDs to indicate the digit's position. Like the single-digit numitron clock, time is displayed by showing each of the 4 digits (as in HH:MM). But for a "clearer picture", I added the above-mentioned 4 different color LEDs. One of its nice features is that it works on the rechargeable 3.7V LiPo battery. The clock does not have an on-board RTC (lack of space), relying instead on the time-measuring capabilities of ATmega328 directly. So this clock will keep time for as long as the battery is kept charged (through the USB power cable). The photo below shows my "collection" of (un-synchronized) micro clocks. (Missing i

There is no "dumb" display easier to connect to an Arduino (or any microcontroller, for that matter) than a numitron tube, even compared with the 7-segment LED display. This is because: unlike LEDs, it does not need current-regulating resistors; unlike LEDs, the segments are not polarized; just connect any end of a segment to Vcc and the other to ground and it lights up; basically, every segment is the filament of a light bulb, like those used in flashlights in the old days; like light bulbs, they even get warm after a while (hence their inefficiency); voltage range is pretty wide, between 2V and 5V; The most popular numitron tube is IV-9, which can be purchased these days on ebay for $5. Size-wise, IV-9 fits perfectly on a Arduino ProMini board, and so it can be soldered directly into the bottom holes of that board. The clock I made displays the HHMM-formatted time as a sequence of 4 digits. Since there is no RTC on board, the processor keeps track of passing time. The rech

I recently had the opportunity to acquire a few HDSP-2534  smart alphanumeric displays on the cheap. They seem to be vintage electronics (mines are stamped 9802, by HP), but they are still being made by Avago and sold by digikey (for about $40 a piece). From the datasheet, the HDSP-253x looks like the LED dot-matrix equivalent of an HD44780-controlled LCD display: data is sent on a 8-bit bus; ability to decode 128 ASCII characters, which are permanently stored in ROM; allows definition of 16 user-programmable symbols that are stored in the on-board RAM. I wired the display to an ATmega328 (internal oscillator at 8MHz) through a 595 shift register, using the schematic in this post from nycresistor blog. They use the HDSP-2111 display, which is very similar to the HDSP-2534 I have. They also provide demo source code for writing data to the display. Needless to say everything works as described. My contribution to the code is a function that sets the display brightness at one of the pr