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3091  Using Arduino / Project Guidance / Re: Vin power and usb Arduino mega on: May 22, 2011, 02:06:11 pm
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External power has priority over USB power if both are avalible.
As see it the external power has priority over USB power only when VIN (which is after the input diode D1) is greater than 6.6 volts. 

By the way, it appears to me that there are two problems with this design.  (1) Since the voltage regulator is a low-dropout device it will function properly when VIN is greater than 6 to 6.1 volts.  This gives you a 0.5 to 0.6 volt range where both the external power and USB can be supplying "+5v".  They are not likely to be exactly the same so something bad is happening somewhere.  (2) When VIN is either not connected or lower than 6.0 to 6.1 volts then the three-terminal regulator is not delivering power.  The USB supply will be applying +5V to the output terminal of the regulator and the regulator will be reverse-biased in terms of VOUT vs VIN.  I don't see any reverse-bias protection for the regulator as recommended in the various application notes that are out there.


Don
3092  Using Arduino / Microcontrollers / Re: Similar Microcontrollers to Arduino/Atmega?? on: May 21, 2011, 03:11:41 pm
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Perhaps I haven't been programming long enough ...
The understatement of the year.

 Thank's for your reply cr0sh, you saved me a lot of typing.


Don
3093  Using Arduino / General Electronics / Re: protecting an mcu from a relay on: May 21, 2011, 02:52:49 pm
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from a dead r/c airplane, so that i may be able to re-purpose it for ground vehicles.
Have you checked into the legality of doing this, or don't you care.  The folks trying to fly their airplanes near your ground vehicle might care.

Don
3094  Using Arduino / Displays / Re: LMC-SS2A20 2x20 display on: May 21, 2011, 08:03:30 am
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Bad news is that it doesn't seem to match up at all with the table here: http://www.ladyada.net/learn/lcd/lcdshield.html
If you are talking about the table where it says "Shave & a haircut - 4 bits!" then I agree with you - it doesn't seem to make sense..  When I get a chance I will try and figure out where they went wrong.

The pin numbers are standard for all of the Hitachi compatible devices.  Use the tutorial that I mentioned in my first reply.  Your physical setup will look different since your pins are oriented in two parallel rows but the pin numbers will coincide.


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Good news is I've got the display logic and back light working fine.
Did you get the single row of blocks and can you vary their intensity with the potentiometer?  If yes then you have already completed the hard part.  Just connect the other six wires to the Arduino, and make sure to ground pin 5 of the LCD module.  You can use any of the Arduino pins for any of the 6 connections to the LCD data and control pins, just make sure that the LiquidCrystal lcd() information matches your connections.

Don
3095  Using Arduino / Project Guidance / Re: Powering Arduino with 12V, 7.5Amp - doable? on: May 21, 2011, 07:50:12 am
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if external power supply is putting our 12VDC, 7.5amps...
The external power supply provides a fixed 12 volts.  If you do not connect anything to the supply then it will be 'putting out' zero amperes.  Whatever you connect to the power supply draws a specific amount of current from the supply.  If you connect one LED with the proper series resistor then the supply will be 'putting out' 20 mA.  If you connect two such LEDs (in parallel) then the supply will be 'putting out' 40 mA.  This particular supply can power any number of devices until their total current demand reaches 7.5 amps.  The current rating of a power supply is like a speed limit.  You can safely draw any amount of current up to this limit.  You can also get away with drawing more current, but you are likely to get in trouble if you do. 

Whatever current goes out of the + terminal of the power supply must ultimately go back into the - terminal.  Therefore the size of the wire has to be appropriate for both + and - power supply leads.


Don
3096  Using Arduino / Displays / Re: LMC-SS2A20 2x20 display on: May 20, 2011, 10:09:55 pm
As far as I can tell it uses an NT3881 controller which is compatible with the Hitachi HD44780.  This means that it should work with the LiquidCrystal library.  I suggest that you follow the tutorial at http://www.ladyada.net/learn/lcd/charlcd.html and see if you can get it working.

Don
3097  Using Arduino / Displays / Re: why MAX7219 SEG DP overload on: May 20, 2011, 05:41:58 pm
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perhaps I don't have it wired correctly ?
Perhaps.

Don
3098  Using Arduino / Displays / Re: GLCD help on: May 20, 2011, 09:32:31 am
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I think I need a -10Vdc source.  What is the best way to add the negative supply voltage?
You are misinterpreting something, doing something wrong, or you have a bad device.  Pin 18 is the negative supply source and you adjust it to give -10v by use of the potentiometer.  Can you supply a picture of your setup?

Although your datasheet says otherwise you may have a device that requires a slightly positive voltage on pin 3.  You could try this:  Connect one end of a potentiometer to pin 18 and the other end to +5.  Connect the wiper to pin 3 and adjust as required.  This is almost the same setup as I gave you in reply #1 except that the potentiometer connection that used to go to GND now goes to +5V.  Check out this thread: http://arduino.cc/forum/index.php/topic,60058.msg433033.html#msg433033 especially replies 4 and 5. 

Don
3099  Using Arduino / LEDs and Multiplexing / Re: Matrix: how does it work and how can i make one? on: May 19, 2011, 10:34:23 am
I found this in a few seconds using Google.  I searched for 'keyboard matrix'. http://www.dribin.org/dave/keyboard/html/

Don
3100  Using Arduino / Microcontrollers / Re: Arduino chip on a breadboard - can't get it to work on: May 19, 2011, 06:40:46 am
From reply # 8:
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The first two numbers are the actual number and the third is the number of zeros you add. So for 221, you have 22 plus one zero, so 220. For 220, it's 22 plus zero zeros, so just 22.

And this differs from the answer in reply #7 by ....?

Don
3101  Using Arduino / Project Guidance / Re: Designed an Attiny "BBB" type board, need input on: May 18, 2011, 03:12:36 pm
You really should move your capacitors around a bit.  The upper 100 nF capacitor should be on the left side of the regulator next to the pin it is bypassing. The center capacitor should be connected directly to the output of the regulator, not at the far end of the Vcc line.  The lower 100 nF capacitor should be as close to pin 8 as you can get it.  You should also identify pin 1 on the ICSP connector.

Don
3102  Using Arduino / Project Guidance / Re: Designed an Attiny "BBB" type board, need input on: May 18, 2011, 01:46:45 pm
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The separate power pins should line up with the breadboard power rails on standard modern breadboards, something I really like about the BBB.
Shouldn't the three pins be offset 0.3" to the left in order to line up with the breadboard power rails?  Maybe I'm missing something....

Don

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The offset matches (more or less) the BBB I have in front of me, I think I'm going to change it to a single 7 or 8 pin connector if I can make it route nicely though.

In order to match your pc layout I am assuming that your breadboard will be orientated vertically with the blue '-' rail at the left.  The red '+' rail will be directly to the right of that and another 0.3" to the right is where the main field of horizontally connected rows begins.

As I see it the five pins in the upper left of your board are going to plug into the five of these horizontal rows on the breadboard.  Any pins that are either 0.1" or 0.2" to the left of these five pins will not have any breadboard holes below them to fit into.  In your design one of the power pins (at the lower right) will fit into the breadboard and the other two will not.  None of them match the red and blue power rails.  Tell me what I have misinterpreted.

You probably should also  have the ICSP pins and the IC further to the left.


Don
3103  Using Arduino / Project Guidance / Re: Designed an Attiny "BBB" type board, need input on: May 18, 2011, 10:38:39 am
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The separate power pins should line up with the breadboard power rails on standard modern breadboards, something I really like about the BBB.
Shouldn't the three pins be offset 0.3" to the left in order to line up with the breadboard power rails?  Maybe I'm missing something....

Don
3104  Using Arduino / Microcontrollers / Re: Arduino chip on a breadboard - can't get it to work on: May 18, 2011, 09:37:14 am
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...first two figures are the value and the third is a multiplier...
That works for color coded resistors.  When there are digits then the third value is the number of zeroes.

Don
3105  Using Arduino / Displays / Re: Scroll LCD bottom line on: May 17, 2011, 08:33:02 pm
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From my reading, it sure seems true what you said.
Would I lie to you?

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I thought by now a library might have developed.
That's not as easy as it may seem due to the wide variety of displays that are run from the same (ancient) controller.  For some insight into the problem check out the LCD Addressing link at http://web.alfredstate.edu/weimandn.

Don
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