Well when I said cheap I meant under $1   I need crap-load of them. Cheapest one I see on e-bay are $3-5 but that's for 2 GB. I'd be happy even with 8 MB, but doesn't look like there's price = capacity correlation
I'll try Craigslist and free-cycle   I had a bunch of 32 and 64 MB cards that I threw out... and now I need it, oh well

Can someone recommend source for cheap small capacity (32 Mb or more) SD cards?  Need it for Arduino project...

If the Geiger detector has a TTL (5V) Serial interface you would just connect the detector Ground to Arduino Ground and the one or two serial pins to one or two Arduino digital pins.  Then use SoftwareSerial to talk to the device.

If the Geiger detector has an RS232 Serial interface you need an RS232-to-TTL level converter between it and the Arduino.

It's ATtiny2313 based (MightyOhm geiger kit), form what I can tell it's straight ATtiny2313 to serial header (no other ICs other than 555), but it's 3 Volt based, so that could be a problem?

I have ATmega based Geiger detector that has serial interface. How would I setup Arduino Uno to receive data from it?  Any hints are much appreciated
Ideally I want to use SD DataLogger shield to log CPMs from geiger detector (without computer).

I also thought about calling the worker-function automatically in a timer interrupt. This should be possible, but only if that interrupt is set to non-blocking to guarantee the main audio interrupt the maximum priority. Maybe I will try to implement such in a next version of my lib, so that calling worker() is not necessary then anymore.

That would be awesome!

To your question about other Audio-Playback-Shields: As far as I have seen it, all other audio-shields contain a dedicated processor that reads the audio-data from storage and feed it to an audio-DAC. For a good sound the DAC must be feed with low jitter at the audio rate of the audio material, otherwise you may recognize audio distortions like slowdowns or stuttering. With a dedicated processor it doesn't matter what your Arduino does while audio is playing, but my library is for all those who don't want to spend extra money to such a thing. SimpleSDAudio get the most out of the AVR's by pushing the Arduino processor strongly to its limits - that's the price you have to pay if you want nice audio from that little thing.

Thanks for the info!
I think MP3 decoder shield might have such processor, but not WaveShield. From description they only have DAC with some basic low pass filters.
BTW, I'm just trying to understand how things work, not in any way implying anything bad about your library. In fact I think it's brilliant work, nobody else did anything like this with no external hardware (other than SD card)!

Don't quote me on this, but from looking at the code, I think you could do such given that you make a call to the SdPlay.worker() function often enough to keep the buffer filled. I'm not sure how much of the processor is left once playing audio, but it seems you could squeeze in a few other non time dependent things. (Like adding up time or checking for a button and updating its state...simple things)

From what I have gathered, the SdPlay.worker() function reads the next sector of the sdcard into a buffer. So if you call it often enough, you should be okay, just don't ask for anything that needs a ton of resources while playing audio.

Feel free to correct me if I'm wrong, but this is what I have gathered so far.

Edit: Just from playing with the serial I can see what you are saying, but I haven't come up with a solution.
Edit2: If you hear the skip when using serial at 9600, move it to a higher speed. I'm running at 115200 just to see, and there isn't a noticeable skip when using the serial commands in the demo.

No you are right, my thoughts exactly (about buffer). I also guessed that increasing baud rate will improve things, but never tested it so you just proved it It makes sense. However I'm just wondering how did they pull off the trick with WaveShield? I can do lots of heavy things with microprocessor while wave is playing, it never skips a beat... Can same be accomplished with this library?   Or because there's no DAC it's impossible to do?  I'm curious to hear what author thinks.

Fantastic library, got it working within few minutes!  
Is it possible to play Audio in parallel while Arduino does other things?  I wasn't able to figure out how. I wanted to see if I can dump WaveShield in favor of this library. WaveShield allows me to play Audio regardless of other things I'm doing, which is essential for my Alarm clock (shows time, blinking dots while playing alarm audio file).
I did some testing with SimpleSDAudio and it looks like if delay between calling SdPlay.worker() greater than 5 milliseconds, playback slows down and becomes choppy... Even calling Serial.println ("test") slows down playback noticeably. Here's example of code from loop:

Code:

void loop(void) {
  Serial.println ("running");
  //delay (5);
   if (!SdPlay.isPlaying() ) SdPlay.play();
  // Let the worker work until playback is finished
  SdPlay.worker();
 }

Let me know if there's a trick to it
Maybe buffer can be auto-filled by Interrupt?

The LM1117 v.reg is a good choice, and I use them too. They say 800 mA, but you need to
also take into account power dissipation relative to actual load current for your app.

Take note of the Thermal Resistance, Junction to Case values shown on page 5 of the d/s.
Eg, the SOT-223 devices get almost 2X as hot as the others for the same load currents.

Thanks, that's good to know! I just ordered TO-220 package, so it should stay cooler...

I always use the "LM1117". Can output a maximum current of 800mA.
It's really easy to find in stores, exists in DIP and SMD models, and is really cheap.
http://www.ti.com/lit/ds/symlink/lm1117-n.pdf

Thanks!   Looks like just what I need

Which voltage regulator would you recommend for SD/MicroSD card VCC power? My input is 5 Volts which powers ATMega644p, so I need to down-convert it to 3.3 Volts to supply power to MicroSD card.  Again this is just to VCC card, I already purchased CD4050BE HEX converter data voltage lines.
SMD or Thru the hole are both ok Looking for most efficient one...

It is hard to say about switching power as your schematic doesn't show any amplifier.
If anything, a PNP transistor or P-channel MOSFET could be used as a switch in the power line to a LM386.

I didn't have it there at a time,just added. Will it work like described with NPN transistor?

google ferrite beads.

Good idea about using ferrite! Thanks a lot!

I mean start making it into a neat assembly. The prototype works, yes?  Now neaten up the wiring so there is not such a jumble of wires.
When current flows and signals change state, they emit energy, which is being picked up & amplified by wave shield.

Thanks!   I made some progress btw.  Looks like main issue was breadboard wiring. I rebuilt amp using LM386 chip and soldered everything to a perfboard. Now noise is almost gone, it sounds very acceptable.
But I still want a way to turn off/on power to the amp on demand from ATMega chip. Anyone done something like this? I presume NPN transistor should accomplish task, but I never worked with transistors...

Gotta clean up the wiring to start. Its a little antenna farm now, lots of radiating sources.

Not sure what you mean? If I remove wiring it won't work...

Also, try putting some caps across pins 5/6 on WS2, see if that quiets the power supply noise some.

Cool! I'll give it a try, thanks!

Without seeing your schematic it's going to be hard for anyone to help you.

A gut feeling would be lack of or insufficient decoupling though.

Sure, here it is.

Just like you I also just started to learn routing on PCB.  They way I found best for myself is to use auto-route and then go by hand over power traces and make them from 16 to 24 mils.  I would just I think 50 is overkill, take a look at official Aruduino board, I didn't see any bigger than 34.