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16  Forum 2005-2010 (read only) / Development / Re: Cheaper TouchScreens for Arduino on: September 17, 2010, 01:09:30 am

That's the best I have seen, too.  It has some library support.  Still, it looks like it uses a lot of I/O pins and is not really inexpensive.  I'm wondering how the big guys go about sourcing LCD Touch Screens?

As an example, while searching for them, I ran across this video player with 320x240 touch screen for $40 from Amazon:

Anybody know how they can offer such a product at this price?
17  Forum 2005-2010 (read only) / Exhibition / Re: New method of using Arduino Diecimila as progammer on: December 18, 2010, 01:43:38 pm
It appears you are using the Diecimila only for its FT232RL chip.

Could you use just an FT232RL breakout board like from Sparkfun, $14.95, or am I missing something?
18  Forum 2005-2010 (read only) / Exhibition / Re: Multiple Buttons on 1 analog pin on: August 30, 2010, 08:04:46 pm
To unambiguously decode multiple, simultaneous buttons, binary weighting for the button values seems like the way to go.  This can be done by connecting the buttons to an R-2R ladder network.  There is a good article on this at

If all resistors and the reference were perfect, best possible resolution would be 10 buttons - one for each bit of ADC converter accuracy.  In practice, 8 buttons may be readable in any combination if the ladder is constructed from 0.1% precision resistors.
19  Forum 2005-2010 (read only) / Exhibition / Re: Do you make your own arduino's? on: November 29, 2009, 11:13:56 pm
If I am thinking of making a circuit board for a shield, I find it quite easy to plop down a microprocessor footprint and associated circuitry right on the board.  With this approach, no Arduino board is necessary.

For programming, it is easy to tack solder the 5 connections for an external serial USB board, creating a temporary programming dongle.  Plug in a processor with a boot loader, tell Arduino's IDE you're connecting to a Duemilanove with 168 or 328, and it uploads your code and supports serial communications just as if you're using a real Arduino board.  This approach worked fine for an update of my Arduino Whole House Telephone Intercom.  

See for a 3D CAD rendering of the board.  Since that page was posted, I have built a working copy and programmed it using this technique.
20  Forum 2005-2010 (read only) / Exhibition / Re: Useing more then 8 Custom Charicters on an LCD on: September 19, 2010, 06:18:30 pm
Have you successfully executed your code example?

I tried something similar, but could not get it to work.  I was afraid newly created characters would replace custom characters previously written.  The actual result was even worse.

For me, createChar() had no effect unless followed by begin().  That is the way its usage is described in the documentation.  begin() clears the screen, so any previously written characters disappear.

It would be nice to get your scheme operational somehow.  It would make character LCDs much more versatile.
21  Forum 2005-2010 (read only) / Exhibition / Re: Video Greeting Card - Arduino Style! on: September 15, 2010, 10:45:28 pm

Where did this TV library come from?  I do not see it listed on the Libraries page.

I suppose these days, as NTSC rides off into the sunset, we'll need one with HDMI output.  Is this feasible?  (I have no idea how HDMI works.)  Maybe with fancy 3D character renderings, too. :-)
22  Forum 2005-2010 (read only) / Exhibition / Re: Two Pushbuttons on One Input for More I/O on: July 08, 2010, 11:19:11 pm
I would want to measure the actual voltage at the input pin when no switches are pressed to see if a valid logic voltage is present. A high value pull down with the internal pull up enabled may not be valid.

If the Atmel data sheet can be relied upon, input current (with pull-up disabled) for voltage between 10% to 90% of Vcc should be within +/- 10 uA.  Through 150K to ground, that comes to +/- 1.5 V, well below the approx. 2.6 V threshold between LOW and HIGH readings.  (The input protection diode limits negative voltage to approx. -.6 V.)  The pull-up value is 20K - 50K, yielding a HIGH input voltage of 3.75 - 4.41 V.  Again, this is well above the threshold.  +/- 10 uA would affect this by less than +/- 0.02 V.

Using a triple voltage divider wired to a analog input pin is a better solution in my opinion.

After posting this, I was thinking of a possible improvement using a binary weighted voltage divider.  I suspect one could unambiguously decode 4 buttons with a single analog input, and maybe 8.  This approach has the advantage of detecting *any* combination of buttons, even if two or more are simultaneously pressed.  Figuring out the necessary tolerances began to make my head hurt, though.
23  Forum 2005-2010 (read only) / Exhibition / Re: Two Pushbuttons on One Input for More I/O on: July 08, 2010, 08:35:45 pm
But how can you see the diference between the high from the pull-up and the high from the button?

Do digitalWrite(buttons, LOW) to disable the pull-up, read the input, then digitalWrite(buttons, HIGH) to enable the pull-up and read again.  The input will follow the written values only if neither button is pressed.
24  Forum 2005-2010 (read only) / Exhibition / Two Pushbuttons on One Input for More I/O on: July 08, 2010, 08:19:48 pm
If you are using pushbuttons and don't quite have enough digital I/O, here's a little trick to free up a pin or two.
  -|_  PB1
   + |
     / 20K
     \_______________\ To AVR
     |      \        / Input
   +_|      /
  -|_  PB2  \ 150K
   + |      /
     |      \
     |      |
    Gnd    Gnd

If neither button is pressed, the input should read high when its internal pull-up (20K - 50K) is enabled, and low when its pull-up is disabled.  If the top button is pressed, the input will read high with or without the pull-up.  Similarly, if the bottom button is pressed, the input will "stick" low.

A drawback: if both buttons are pressed, the input will read the same as if only the bottom button were pressed.
25  Forum 2005-2010 (read only) / Exhibition / Re: Backlight driver on: June 22, 2010, 11:59:49 pm
I generally agree with retrolefty.  Logic level N-channel MOSFETS are usually an excellent choice.

However, I just realized part of the original post was:
I have the controller running at 3.3V and 8MHz...
 With only a 3.3V output, you don't meet the threshold for driving logic level MOSFETs.  Looks like your NPN bipolar may be the best choice after all.
26  Forum 2005-2010 (read only) / Exhibition / Re: Backlight driver on: June 22, 2010, 08:07:42 pm
What I did today is probably not so cool for the electrical engineers here...

Well, I'm and electrical engineer and your idea sounds pretty cool to me.  I do not know how to read a .svg file (do you have something more accessible?) but I get the general idea.

I have found the PWM output a handy source of switching signal for voltage boost circuits, with the added bonus that you can start and stop boosting at will.  Maybe you want to try flashing the backlight to get attention for an alarm condition.

Initially I intended to use a FET but then learned that the FET appears as a capacitor for the AVR output and might damage it.

If you are talking about FET gate capacitance, that is usually a very small value.  Also, AVR outputs are relatively robust.  There is a good chance the transistor has a base capacitance value as large as the FET's gate capacitance (drill down in your data sheets!) but it draws so much current the capacitance is considered negligible.  With the FET, capacitance is all there is.  The transistor is almost certainly a heavier load for the AVR output.
27  Forum 2005-2010 (read only) / Exhibition / Arduino Contour Lawn Sprinkler Proposal on: April 05, 2010, 11:19:09 pm
I ran across a microprocessor controlled garden sprinkler recently - the Gardena "AquaContour" large area sprinkler.  A video is available at:

Though it is clever, I found myself disappointed with this device. Here are some features that seem to be missing:
  • Ability to skip over no-water areas and irrigate areas beyond them
  • Programmable for multiple zones, some of which are remote from the sprinkler
  • Even water distribution (I could find no such claim, and the video makes it doubtful)
It seems like a single nozzle under Arduino control should be able to cover the missing features.  I am thinking of a nozzle with precise rotary control, and fairly nimble azimuth control.  The combination would determine where the single stream of water strikes the ground at any given moment.  It would be programmed to strike all target points with duration a function of distance, to assure even coverage.  It would move across non-target points at maximum speed.  (A little water would fall on non-target points with this scheme.)

There is nothing to prevent me putting in standard pop-up sprinklers in my own yard, which I plan to tear up anyway.  Thus, my motivation to do this project is not very high.  I just thought I would toss out the idea in case somebody wants to pursue it.
28  Forum 2005-2010 (read only) / Exhibition / Re: Whole House Telephone Intercom on: February 13, 2010, 08:15:33 pm
A ready-to-install commercial version of this intercom is now available, the Add-A-Com Whole House Intercom for Standard Telephone Systems.

Review and order from the product page at

A User Guide is available for download at
29  Forum 2005-2010 (read only) / Exhibition / Re: Whole House Telephone Intercom on: January 16, 2010, 12:35:06 am
A few first generation boards are now available:

Full details at
30  Forum 2005-2010 (read only) / Exhibition / Re: Whole House Telephone Intercom on: September 16, 2009, 10:41:26 pm
I plan to make the single PCB version available assembled and tested if there is enough interest.

If you are interested, you can let me know, and register to be notified upon availability, by using the form here:
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