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31  Forum 2005-2010 (read only) / Development / Editing nets in Eagle on: July 27, 2009, 10:06:37 pm
Maybe I'm just blind to it, but I accidentally joined two nets that should be independent and I can't find any way to break them apart.  Is there no function to directly edit which nets are joined to which others?  
32  Forum 2005-2010 (read only) / Development / Re: 1 chip Arduino on: July 25, 2009, 08:15:34 pm
You pretty much can, yes, if you use the internal oscillator.  Otherwise at the very least you need a crystal or resonator.  You can check out this topic for how to run from the internal oscillator.  However, there are some advantages to using a more complete unit, such as onboard programming header & reset button, onboard voltage regulation, onboard reset switch, all of which are optional but make things much easier, and you can get them in various combinations on breadboard-friendly units.

There's another person on this forum working on breadboard compatible arduino form factor: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1239733868

As well as a couple of commercially produced options:
http://www.ladyada.net/make/boarduino/
http://www.moderndevice.com/RBBB_revB.shtml

I'm partial to the RBBB myself, since it's a bit narrower than the Boarduino and you can cut off the power section to make it shorter (I use a regulated supply for breadboarding anyway, so it's not really necessary).

Note that some of the smaller units don't have USB onboard, so you need something like this as well: http://www.sparkfun.com/commerce/product_info.php?products_id=9115

A separate USB-Serial adapter is also useful if you want to build custom boards down the road and don't want to have to incorporate a USB converter onto each one.

As to the bootloader, you only need to mess with that if you depart drastically from the standard Arduino design (using a different AVR, different clock speed, IE).  Otherwise, you can just pick up a pre-bootloaded 328 or 168 from any Arduino-friendly store and put it straight to use.
33  Forum 2005-2010 (read only) / Development / Re: Call for Favorite Connectors on: July 20, 2009, 09:56:56 am
It depends a lot on how frequently you need to make/break the connections and how much physical abuse they'll be subjected to.  Don't forget to consider what type of cable you're using, and proper strain relief where applicable.  

Where durability is important, frequent make/break, and with low pin counts like yours, Neutrik's screwless XLR connectors are great.  Rated 5-16A per contact (depending on number of poles), available with 3-7 poles, positive locking, and have good strain relief built in.  Stay away from any connectors that have tiny screws holding them together, especially XLRs.  

If the assembly is subject to vibration and/or user-accessible, Molex style friction lock connectors are a good choice if you don't need to make/break often.

34  Forum 2005-2010 (read only) / Development / Re: CompuBlino Arduino based computer bling on: June 15, 2009, 10:50:32 am
Why don't you use the 5V from the computer PSU directly, and have another connector that feeds into a regulator for non-computer applications?  Not unlike how the Arduino boards cen run directly from USB power or internally regulated power via a separate connector.  As it is, since you're regulating 12v from the floppy drive connector down to 5V, the regulator will be dissipating 1.4x the power used by the board straight to heat--not very efficient.
35  Forum 2005-2010 (read only) / Interfacing / Re: 24x[5x7] led matrix on: May 29, 2009, 04:44:26 pm
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I don't quite understand why you would want to use an arduino without all of the boards. Presumably with the keyboard input it is designed to have some kind of temporary memory to store messages...

If the keyboard connector is non-standard and the RS-232 undocumented, then you may not have a choice but to replace the processor module.  Or it could be that the processor module doesn't have any functionality for graphics, or something, that you want it to do.

From the pic and your description, it seems the discrete transistors control power to the rows, and the shift registers feed data to the transistor arrays to control power to the columns.  The registers are probably daisy chained so that one feeds into the next as data is shifted in, likely in pairs with a single data line to each pair, and a single clock line to all 8.  The caps look to be just decoupling caps, and the resistors limit the current to each column.  

So the controller pumps the data for the first row into the shift registers then turns on the first row transistor for a period of time, turns the row off, pumps in new data for the second row, and then turns on the second row transistor, etc.  

As far as the cable, you probably have the 7 control lines for the row transistors, maybe a signal ground if it's not just using the PS connector ground, then for the shift registers a clock line, a clear line, and at least one data line.  There might be more then one data line so that the controller can fill the shift registers faster.  IE, data1 to SR1, chained to SR2, data2 to SR3 chained to SR4, etc.  That means sending 4 bits 8 times rather than 1 bit 64 times, so much faster.

Other than that you'll have to start examining traces and poking it with a meter, but I hope this helps.  smiley
36  Forum 2005-2010 (read only) / Interfacing / Re: DMX woes... on: September 16, 2009, 11:26:59 pm
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Just for the sake of curiosity, I knew DMX is a protocol to control complex lighting. What can you do by receiving and not sending it?
DMX is a one-way implementation of RS485, with the controller sending a byte value for each of up to 512 channels to be received by up to 32 physical devices on the DMX chain.  So in normal operation, you have one device sending only, and up to 32 devices receiving only, Hence the need for complementary one-way devices to have a functioning DMX network.

Of course, two way communication can be quite valuable, so modern systems sometimes provide for it through RDP, but relegate device->controller communications to a separate pathway.

The spec requires a 5-pin XLR connector with two twisted pairs wired through.  The first pair is used for DMX data, naturally, and originally the second pair was reserved so that a second "universe" (set of 512 channels) could be carried on the same physical network.*  In modern practice however, where the second pair is used at all it's often used for RDP, which allows devices to report status information back to the controller.  That way you get two-way communication, but the first pair is kept to vanilla one-way DMX to avoid confusing less intelligent devices (of which there are many *cough*Leviton DDS packs*cough* on the market).  

* DMX/other control over Ethernet protocols used in modern infrastructure have largely obviated the need for 1024 channels on a single DMX physical interface.  Larger installations generally use an Ethernet 'backbone' and convert to DMX near each gear position.  Some applications may see Ethernet run directly to specific fixtures (such as High End's DL.2) as well.  This left the idndstry pretty much free to find other uses for the second pair, such as RDP.  There might have been some products out there that used the second pair to send power to accessories as well, but the industry has standardized on different cable (one twisted pair for data, and a larger gauge pair for power) terminated with a 4-pin XLR for such things--color scrollers, pattern rotators, motorized irises, to name a few--nowadays.  
37  Forum 2005-2010 (read only) / Interfacing / Re: Waterproof Components? on: October 17, 2009, 12:05:12 am
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Quick question on the capacitive button option, I assume the problem with large amounts of water is related to false button presses? If this is the case is there a way that you know of to "debounce" this kind of input?


Basically, you'd get multiple key presses to keys 'bridged' by water with which ever one you actually touched.  Or at least that's what I've read, I've never bothered to play with touch sensing.  A way to combat that would be to reject multiple simultaneous presses, and maybe also only register a keypress once the key has been released within a certain window after the initial press, although that would prevent you from being able to 'hold down' a button to scroll or run a value up and down--the touch buttons on my laptop are like that, it's obnoxious trying to run the volume up or down by mashing the button with no tactile feedback.
38  Forum 2005-2010 (read only) / Interfacing / Re: Waterproof Components? on: October 16, 2009, 11:06:07 am
Well, the LCD is easy, just stick it behind some plexiglass that is sealed to an opening in the enclosure, or use an enclosure with a clear cover.

You could do capacitive buttons, but a large amount of water on the face can cause problems.  The advantage is that these too could be mounted to the back of a clear cover just like the LCD, so you'd need to make exactly 0 openings in the face of the enclosure.

Discrete waterproof buttons tend to be fairly bulky. . .

You could build your own membrane keypad that could be sealed to the face of the enclosure.  No real tactile feedback, though.

You could mount tact switches behind a flexible membrane.

Alternatively, you could also get something from OKW, you can search by IP Rating according to what your needs are under the Sealed Enclosures dropdown menu. Depends where you want to land on the good/easy/cheap triangle.
39  Forum 2005-2010 (read only) / Interfacing / Re: emg signal + robot hand on: June 09, 2009, 09:22:58 pm
If you're constructing the filter/amp circuit yourself, why not do so such that the output is restricted to 0-5V?  
40  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 16, 2009, 01:53:30 pm
The datasheet indicates that your matrix can be driven at 30mA per LED at 10% duty cycle which would give you a brighter display, but if you're okay with the brightness at 20mA, then that darlington array will be fine.
41  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 16, 2009, 02:04:37 am
4051 can only output up to 25mA.  Your row driver needs to be able to supply enough current for every LED in each row, so 24 * If  (480mA if you drive each LED at 20mA).  You will need some sort of current amplification (FET or Darlington) for the row drivers.
42  Forum 2005-2010 (read only) / Interfacing / Re: RC Control on: September 29, 2009, 12:57:29 am
Not unattainable at all.  It's just that an RC car of the toy variety typically has two channels of three possible values each: forward/stop/reverse and left/straight/right.  That means you can send a maximum of 9 distinct commands from the controller to the receiver.  If you go to a fancier RC system as used for higher end RC cars/aircraft/boats, you'll be able to send up to six or so channels of 8bit (maybe?   if you're lucky? depends on the quality of the receiver and environmental factors I would guess) values.  However if you really want to send data and complex commands to and from the robot, you probably want something like XBee, which would provide a wireless serial communications channel between the computer and the robot.
43  Forum 2005-2010 (read only) / Interfacing / Re: RC Control on: September 27, 2009, 11:44:44 pm
There's really not much more "brains" to an RC car than the receiver itself.  The receiver basically just translates the radio data into turning motors on and off.  Of course there's typically some feedback from the steering servo, but that's very basic.  How complex are you thinking of getting?

44  Forum 2005-2010 (read only) / Interfacing / Re: Where do I find an electic door lock? on: November 10, 2009, 12:58:57 am
Use an electric strike, as was posted.  How you interface it with an Arduino will depend on the exact model you get (AC or DC, current and voltage requirements).
45  Forum 2005-2010 (read only) / Interfacing / Re: DC motor selection? on: November 10, 2009, 08:04:33 pm
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The torque needed is something we can't calculate right now


Why on earth not?  You know the mass of the load to be moved and presumably have some target for acceleration, F=MA, factor in the mechanical advantage of your end mechanism, add in mechanical/aerodynamic (if significant) drag, and bob's your uncle, you've got a power figure for your motor+gearing.  
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