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1  Using Arduino / Project Guidance / AA power!!! on: February 08, 2011, 12:30:52 am
Hi all,

I have a Duemilanove/Atmega328 I'm looking to use in a high-altitude ballooning project. I'm faily new to hardware, but after frying a few circuits in the past I already know my major weakness is power. Due to temperature constraints, I'll be using some Lithium AA batteries @1.5V to power all devices, but the number of AAs is an open question. Any excess power converted to heat with my heatsink is a good thing, as long as it doesn't fry anything.
1) my arduino smiley-grin
2) OneWire temp sensor (3-5V, <=18mA)
3) Lassen IQ GPS module (3.3V, 27mA) with antenna
4) SD card writer (via SDuFat), (3.3V, ampage unknown)
5) SMS texting on a Motorola C168i via SSerial2Mobile - I don't think I need any power for this as it survived in my freezer for a few hours without being used. But once I have everything assembled, if it needs more juice to send texts occasionally, this potentially could need power as well

Do you have any suggestions for the number of AAs I should use?
Also, all of my devices use 3.3V. Does the 3V3 socket on my arduino support all of this? Or should I use the 5V socket plus some heat? Or power them directly (plus some heat)?
2  Using Arduino / Storage / uFat empty files on: February 07, 2011, 02:15:35 am
Hi all,

This question is mainly for people familiar with a the SDuFat library

I have an SD card breakout board in the mail to me, but I'd like to get some simple questions out of the way so I can get to work once it arrives. I plan on using it for data logging, no reading required, but over the course of ~3 hours of expected use a good amount of ascii data might be generated.
I'm planning on using SDuFat. Question 1: is this a good idea?
If you agree with my library choice, my next question is about the empty files that this library writes to. Checking out the example code, it uses hola.txt, an empty file with a bunch of blank spaces (0x20) culminating with an EOF (0x03). I figure the following should do the trick for a 256 SD card:
#include <stdio.h>

int main(void)
int i;
FILE *myfile = fopen("emptyfile.txt", "wb");
for (i=0;i<(268435456 - 1);i++) //256mb minus 1 byte
putc(0x20, myfile);
putc(0x03, myfile); //the extra byte
return 0;
The file does end up being 256mb (exactly), but when I open it in a text editor, mine looks completely empty, whereas the empty example file "hola.txt" begins with a character that looks like an L. Do you have any idea why their hola.txt has this "L" character, and why mine doesn't?
3  Forum 2005-2010 (read only) / Interfacing / Re: HT1632 with LED matrix display on: October 08, 2009, 10:22:47 pm
Thanks Bill.
I think there must be something else going on. I made the change, but now it seems to set the LEDs on for 1.5 times then off for 1.5 the length of the board. Ideas?
See video[media][/media]
4  Forum 2005-2010 (read only) / Interfacing / HT1632 with LED matrix display on: October 08, 2009, 08:41:50 pm
Hi all,
I've been following this thread on a similar 16x24 display as a guide to wiring up my HT1632-based 8x32 LED matrix display.
Their datasheet vs. my datasheet

Post #8 on that thread lists some code to turn all the LEDs on, then off for the 16x24 board. Running it after a copy-paste makes the first 24 columns light up as they should, but the last 8 columns are skipped before it starts turning off [see attached image of just before it starts turning off]

I can't find what in the code is causing this. Bit shifting is new to me, and since I'd imagine the problem is in the loop() function, I don't think I'll be able to find it quickly. From my understanding, the first loop is from 0 to 95, the nested one over 8,12,14,15. That's great, but I don't see how it relates to the datasheet for the 16x24 board, much less what I should change for it to work on the 8x32 board.

5  Forum 2005-2010 (read only) / Interfacing / more LEDs than a single MAX72XX can handle on: September 24, 2009, 10:13:23 pm
Hi. I'm new here. I'm also fairly new to circuit design. I've made a few things, but never with a PIC, arduino, or anything like that.

My plan is to wire up a bunch of LEDs in a grid somewhere between 5x16 and 6x17. I'll know my size constraints once something arrives in the mail. Anyways, with one MAX72xx I can (read: will fail to) wire up 64 LEDs, and the datasheet says that more MAX72XXs can be cascaded through DOut->DIn. Does this mean that I can individually control up to 128 LEDs with two MAX72XXs, brightness and all? Or does it just mean that this wiring of two MAX72XXs is achievable, so that each group of up to 64 LEDs behaves identically?

Also, since this thread might attract people knowledgable in similar areas, I have two more questions: 1) Regular LEDs arranged in a grid are smaller LEDs that can be densely packed exist that won't break my budget? 2) Know of a cheaper place than this to buy the 7219 (cheap already, I know, but worth a shot.)?
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