Saturday, April 30, 2011

My Geiger counters

I have had a Geiger counter project on my "todo" list for a long time, ever since fellow Arduino hobbyist BroHogan (aka John) created one  more than a year ago. His Geiger project received a lot of interest lately, with the unfortunate events in Japan, so he decided to provide a kit (which seems, not surprisingly, to be sold out pretty quickly). John graciously offered to send me one of his kits, which I just finished assembling, and I am glad to report on the impressions and results.

First of all, DIYGeigerCounter is a big kit in a small package; it's got more than 40 through-hole parts, on a PCB that would fit in an Altoids gum tin box (Note: only the PCB, not the Geiger sensor itself, which is too long).

The kit contains both the Geiger analog circuit (that generates the high voltage for the tube) and the ATmega328 microcontroller part (that can eventually drive an LCD), together on the same board.

The version I received is 1.0; the version John is selling is 1.4. The differences are minor: the latest revision has the resistors placed horizontally, a few more headers on the processor side and four screw holes in the corners.

Because of the complexity of the circuit, one needs to take the time to read the assembling instructions. There are lots of resistors and capacitors that need to be placed correctly. And then there are the diodes. To determine their orientations (they are not marked on the silkscreen in revision 1.0), one needs to use the continuity meter and the schematic, which is not a bad thing at all, since one learns about the circuit. (I know that the tendency is to just assemble everything in a haste, because I do that myself. I only learn when something goes wrong and the circuit does not work. Then I have to go to the schematic and use the multimeter.) OK, so no shortcuts here; this kit requires a bit of study, checking and identifying the parts, even crossing them off the list once installed (this is what I did).

Needless to say that the kit worked superbly right off the bat. I measured (with a regular voltmeter, not using the method BroHogan describes here) the high voltage, and it is 310V. It may sound dangerous, but I felt nothing when I touched those pads. The assembled Geiger counter is shown below, without the Geiger tube.

Notice the nice clips for the tube. Other kits usually recommend just wrapping some wire around the tube's terminals, or worst, soldering the wires directly to the tube (this procedure may damage the tube, apparently).

The tube I used for partial testing (since I don't have any radioactive materials just yet) was part of another, much simpler (and much more expensive) kit, from electronic goldmine, shown assembled below.

I just inserted the clips over the installed tube and powered DIYGeigerCounter and started clicking (with the LED turning on) every 2 seconds, giving thus a "reading" of about 30 CPM (clicks per minute).

Next step is the addition of the LCD, detailed here. Then, I will need to build and enclosure, so I can take it out on the field and impress my friends when they chose their granite kitchen counter-tops :)

Saturday, April 23, 2011

Scrolling message sign display with Wise Clock 3

A feature of Wise Clock 3 board that was not previously "advertised" is its ability to drive more than one 3216 LED display, making it easy for anyone to quickly assemble a window sign display.

Wise Clock 3 board plugs into both connectors of the display. To cascade a second display, you will need to solder, on the Wise Clock 3 board, a right-angle 16-pin (8x2) male header in the place provided below the existing connector, then use the 16-wire ribbon cable coming with the 3216 display to connect this newly added header to the input connector of the second 3216 display, as shown in the photo below.

A demo (put together by Tim Gilmore) of a 64x16 windows sign display powered by Wise Clock 3 is shown in action in the following video. The demo software can be downloaded from here (for more details see this thread in the arduino forum).

Besides saving more, making your own clock brings a great sense of accomplishment.

Related posts:

Tuesday, April 19, 2011

A new kind of baffles

It started as a challenge, then it became an obsession: the baffles for my own version (still work in progress) of Word Clock, the grid that separates the LEDs from one another, so that every letter on top of a LED can be lit individually.

Baffles for Word Clock clones have been made before, see here and here (part of this and that instructables, respectively). These examples separate groups of LEDs rather than each individual LED. Justin and Anool of ClockTHREE fame raised the bar (they did not call it ClockTHREE for nothing :) with their individually addressable LEDs and the associated baffles, an elegant and remarkable solution, nicely integrated with the board and the case. Trying to replicate their results for just one prototype is both expensive (laser-cutting) and tedious (calculations, drawings, assembly). After a lot of thinking, I "invented" my own solution for the baffles, as shown in the photo below.

Basically, I used 40-pin female headers to separate the low-profile, wide-angle, LEDs. The headers are held in place by soldering them to the prototyping board. For the 8x14 LED matrix, I used about 40 headers, for a cost of about $12.

Generally speaking, designing and making the baffles is a feat. With so many choices, one needs to answer a few questions before designing them:
  • what material should be used (cardboard, plastic, wood etc)?
  • what manufacturing process would be the most appropriate (in terms of price, assembly time etc)?
  • how could they be attached to the board?

Plastic is an obvious choice for the material:
  • laser-cut (expensive, requires the assembly of the parts);
  • mold-injected (perfect for mass-production; no assembly required: what you get is what you use);
  • 3D printed (suitable only for prototyping; may be expensive).

Even after having the baffles made, the question of how to attach them to the board still remains. They need to be placed equidistant between the LEDs and held solidly in place (screwed down to the board maybe?).

Now you don't need to wonder anymore why Peggy 2 does not come with baffles :)