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5371  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 24, 2010, 05:03:39 pm
Your numbers don't add up.  6 AAA batteries provides 7.2 to (over) 9V, depending on battery type.  What battery type are  you using, and is THAT changeable?)

As zoomkat implied, it may be a lot easier to use a capacitor to provide the 50-100mA of "the rest of the circuit" for the duration of servo movement than it is for it to provided the 200-400mA needed by the servos!
5372  Forum 2005-2010 (read only) / Interfacing / Re: Making my own serial interface on: June 11, 2009, 02:56:11 am
The hardware inside the AVR serial port is essentially a shift register plus a bunch of logic to detect beginning and end of characters, plus a clock-rate generator to clock the shift register at the appropriate speed.  (well, double all that since it has to receive and transmit at the same time If you look up older computer hobbyist literature, you can sometimes find "clever" circuits designed to connect to your ASR33 using only TTL logic chips.  I couldn't find anything that looks brilliant, but here are a couple links that might be interesting.  (UART from TTL),M1  (Big discussion on UARTs and serial communications, mostly using stand-alone UART chips.)

You can also find SPI and I2C interfaced uart chips, but they seem to mostly be overpriced solutions for the truly desperate; you might as well use two ATmega8s...  (

but all the PCs I've used over the last couple of decades have tolerated inverted TTL,
being a Mac user I didn't realize how bad PC hardware actually is. If it recognizes 0V as a mark state then it is working way outside the serial spec and will be subject to interference and all sorts of noise.
It's not PCs, it's the rs232 receiver chips.  All the ones I've used (1489, 14506, max232/etc) will treat 0V pretty much the same as -12V or whatever, and the granddaddy of them all, the venerable MC1489 receiver, doesn't even have a negative supply voltage to implement a reference below zero.

What do you EXPECT it to do?  It's not like a modern comm controller where there's a separate "signal good" indication; the output has to be either high or low regardless of what the input voltage is.  At least this way you get to cheat easily (fond memories of connecting the "-12V" supply of the 1488 transmitter to Gnd, "+12V" to 5V, and having my SDK86 talk to my CPM machine "just fine.")

Now, a PC that doesn't TRANSMIT lower than -3V for mark is indeed broken.  ("Be conservative in what you send, and liberal in what you accept!")

(And I bet you're not really sorry that you're a Mac user, either!  ;D)
5373  Forum 2005-2010 (read only) / Interfacing / Re: Arduino voltage regulator question on: June 06, 2010, 08:21:44 pm
Ok...  Rats!  it was such a good theory!
5374  Forum 2005-2010 (read only) / Interfacing / Re: Arduino voltage regulator question on: June 06, 2010, 04:48:55 pm
did you mistype that first sentence?
5375  Forum 2005-2010 (read only) / Interfacing / Re: Arduino voltage regulator question on: June 06, 2010, 02:07:36 am
I can't see where the traces go to tell whether the board has been modified to use the 2940 pinout.  The other components and the relative placement can all stay the same even if you change the regulator and traces to match.  For example, the "freeduino" design switched from a 33269-based design to 7805-based at quite a late time, without needing to change much else.
5376  Forum 2005-2010 (read only) / Interfacing / Re: Arduino voltage regulator question on: June 05, 2010, 03:56:58 pm
there is a L53B 5v voltage regulator (datasheet below) on the board.
Hmm.  My impression was that the DFRduino was a "faithful" reproduction of the Arduino duemilanove PCB, rather than one that had had any re-engineering applied.  If that's the case, then the lm2940 regulator you reference is NOT a correct replacement for the mc33269D regulator used on the original duemilanove!!!!  They have different pinouts!

(Check whether the tab of the regulator has continuity with the metal casing of the USB port.  If the board is properly laid out for lm2940, these should both be GND.  If the PCB is laid out for MC33269D, then the regulator tab will be +5V (vout of the regulator) while the casing would still be GND.)
5377  Forum 2005-2010 (read only) / Interfacing / Re: Connecting Arduino and WRT54GL with max3232 on: March 10, 2010, 06:24:10 pm
You don't need (or want) a max232; both the Arduino and the router are operating at digital signal levels.  Now, the router has 3.3V signals and the Arduino has 5V signal levels, but a max232 is not the right chip to interface them (I guess you COULD use two - one to convert the arduino to rs232 levels, and one to convert the router to rs232 levels, but that seems excessive.)

You may be able to connect them directly.  Sometimes 3.3V chips are "5V tolerant."  Otherwise, the router output is compatible with the arduino input, and the arduino output could use a simple voltage divider to connect to the router input.
5378  Forum 2005-2010 (read only) / Interfacing / Re: Arduino with old Laptop LCD? on: February 10, 2009, 11:08:34 am
Your data general was just a minicomputer!  The one I had in mind was a Decsystem-20, maxed out with 4MWords of memory (36 bits each, so 18Mbytes, sort of.)  The big one had over 2Gbytes of disk, too.  Each disk was the size of a washing machine, and the main cpu/etc cabinet was about refrigerator height by six times as wide.  Not including tape drives.

I was serious about running the whole laptop as the display.  Similar to your picture frame, you'd boot something like DSL, and have it auto-run a terminal emulator.  Minimally, you could then send text to it form the arduino, and do high-res text displays with fancy updating using "escape sequences."  With luck, you could find a graphics terminal emulator that supported line-drawing, downloadable fonts, color, and who knows what else (I'm not immediately aware of such an emulator, but its certainly possible.  We had such a terminal (packaged, not PC-based), connected to the dec20...)  This way, the PC's memory would hold the large bitmaps and the arudino would only have to contain info about the particular graphics objects that it wanted to draw.

5379  Forum 2005-2010 (read only) / Interfacing / Re: Arduino with old Laptop LCD? on: February 10, 2009, 05:23:04 am
Well, the big problem is that the arduino doesn't have enough memory to store a 600*480 image.  That's about 300k pixels.  256RGB is three bytes for each pixel, or almost a megabyte.  The ATmega328 has 32Kbytes of program memory, 2kbytes of ram, and 1k of EEPROM, and even all put together, that isn't enough for one BIT at each pixel location.  The ATmega168 has half of that.  You can do things with characters, and you can do things with sprites, and you can do things with REALLY BIG PIXELS
(32x24 on a screen?), but that didn't sound like what you were after.

("Why yes, the PC graphics card I pulled out of the trash DOES have more memory on it than the entire mainframe I used to use that supported 50+ simultaneous users.  Why do you ask?)

(spoiled young whippersnappers!)
5380  Forum 2005-2010 (read only) / Interfacing / Re: Arduino with old Laptop LCD? on: February 07, 2009, 01:17:16 am
No, you can't.  Unless you want to use the rest of the laptop as a "controller" for your LCD.  (which is actually not all that ridiculous an idea, if the laptop is working at all.  A used laptop of that vintage, or for that matter a brand new PDA, may be a cheaper alternative than a new "standard interface" LCD panel bought as a component.)
5381  Forum 2005-2010 (read only) / Interfacing / Re: Getting Crazy with WiFly Module + Telnet :-( on: May 19, 2010, 07:49:54 pm
SPI_Uart_println("PUT /api/7430.csv HTTP/1.1");
SPI_Uart_print("Content-type: text/csv");
SPI_Uart_print("Content-Length: 3");
SPI_Uart_print("Connection: close");
As shown, you are missing ANY separator characters between fields, and it will all flow together like:
PUT /api/7430.csv HTTP/1.1
Host: www.pachube.comX-PachubeApiKey:XXXXContent-type: text/csvContent-Length: 3Connection: close200
Which is clearly wrong.  You're also missing a blank line between your header and your data, which I think is required.  But you should have gotten closer with the "\r\n" in each line, I would think.  I wouldn't trust "println" to have the right sequence, and would try something like:
SPI_Uart_print("PUT /api/7430.csv HTTP/1.1\r\n");
SPI_Uart_print("Content-type: text/csv\r\n");
SPI_Uart_print("Content-Length: 3\r\n");
SPI_Uart_print("Connection: close\r\n\r\n");  // note extra blank line
Your key doesn't contain any backslash characters, does it?  That would also be a problem unless you double them...
5382  Forum 2005-2010 (read only) / Interfacing / Re: maximum speed PC to arduino on: May 19, 2010, 07:56:46 pm
People trying to use 1000000bps have reported that they have to modify the arduino serial driver (making it somewhat faster) to get reliable operation (and there isn't a lot TO the serial driver.)  So somewhere around 1000000bps is probably the hard limit (I think that may also be the limit of the bit rate generator on the serial port.)
5383  Forum 2005-2010 (read only) / Interfacing / Re: Can 4017 handle this? on: May 18, 2010, 04:58:50 pm
Now, the 4017 can handle 25mA max
No it can't. That is the absolute maximum stress rating
It's also "while maintaining a particular output level", which isn't particularly important in this case.

You know, normally I'm in favor of treating data sheet "max" ratings with some respect, but the 4017 has been used in SO many hobbyist LED projects that I think it has proven itself capable in that role, and your original idea should work just fine.  A carefully calculated resistor value will give you less current than you think, since the 4017 internals are NOT ideal switches; it has some internal resistance as well.

And since the 4017 only drives one output at a time, I don't think you have to worry about overall power dissipation...

It's also pretty rare (I think) to find logic ICs that fry themselves whenever you accidentally short an output pin to a supply rail, even for "moderate" lengths of time.
5384  Forum 2005-2010 (read only) / Interfacing / Re: Crystal Oscillators for time on: May 18, 2010, 10:39:08 am
The other trick is to use the AC power supply to provide a time reference.  In the US at least, the "60Hz" of your typical wall outlet is kept VERY accurate over the long term...
5385  Forum 2005-2010 (read only) / Interfacing / Re: Sparkfun's Breakout Board for microSD Transflash on: May 15, 2010, 11:29:15 pm
Better check your flash card device specifications.  It's basically the same technology as serial eeprom/flash, and has similar limits on the number of times it can be written.  The "smart" controller in a micro-SD may or may not do "load leveling" across the memory cells to extend the life.  You might want to look at "FRAM" instead, depending on how much space you need (FRAM isn't as dense as flash, but it can be written essentially an infinite number of times.)
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