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1  Forum 2005-2010 (read only) / Development / Re: Behind the scenes of a photocell--what's going on? on: April 28, 2009, 11:38:24 pm
you're very welcome.
2  Forum 2005-2010 (read only) / Development / Re: Behind the scenes of a photocell--what's going on? on: April 28, 2009, 04:47:03 pm

Where 0V should be 0/1023 and 5V should be 1023.

ADC reported value = (Input Reading / Reference Voltage)*1023


You make a voltage divider with two 10k resistors. One end connected to 5V, one end connected to ground. If the resistors are exactly equal and the voltage supply is exactly 5V, this should be the result:

2.5V on the input pin (Input Reading) with a voltage reference of 5V (default on most boards)...

(2.5V/5V)*1023, which is around 511 to 512.

By changing the resistor in series with your photocell (while tapping your voltage reading at the junction of the two resistors), you're changing the ratio of the two resistances, thus changing the voltage at the tap/junction.

Voltage Reading = [Rphotocell / (Rphotocell + Rseries)] * 5V

Say you had a 10k Rseries and your photocell was at 5k due to lighting conditions:

Voltage Reading = ( 5k / 15k ) * 5V = 3.33...V

Your Arduino should report:

(3.33V/5V)*1023 = 682


By the way, the 1023 comes from the fact that the ADCs present on the ATMEGA's analog pins is 10-bit capable.
2^10 - 1 = 1023, which is the number of voltage levels it is capable of discerning between.

A 24 bit ADC (found in high quality digital audio I believe) would be able to discern between 2^24 - 1 or 16.7M (16,777,216) levels.

I was rather thorough, hope this helps.
3  Forum 2005-2010 (read only) / Troubleshooting / Re: How to get a stable reference voltage? on: May 20, 2009, 09:26:14 am
For temperature related stuff I use an LM336-2.5 for a 2.5V reference, they come in other "denominations" too. Pretty damn accurate.
4  Forum 2005-2010 (read only) / Troubleshooting / Re: Mr +5v meets Mr Gnd on: July 22, 2009, 10:38:14 am
oh whoops i forgot you had a nano: the diode is on the bottom side between the yellow capacitors and the power LED. see if that is intact.
5  Forum 2005-2010 (read only) / Troubleshooting / Re: Mr +5v meets Mr Gnd on: July 22, 2009, 10:27:39 am
look at the big surface mount diode on the board, high currents can cause it to crack in half literally.

i can almost guarantee its not the atmega, as no current would have passed through the chip itself.
6  Forum 2005-2010 (read only) / Troubleshooting / Re: Typical Output Voltage on Digital Pins? on: May 16, 2009, 12:55:22 pm
get a new multimeter lol, and not one from radioshack.
7  Forum 2005-2010 (read only) / Troubleshooting / Re: Can't upload to I/O on: April 29, 2009, 12:48:20 pm
Do you notice any LED activity (on pin 13 for example) when you click UPLOAD?
8  Forum 2005-2010 (read only) / Troubleshooting / Re: Did I blow up my Arduino? on: May 08, 2009, 10:07:16 am
Yeah It looks like you did. That part that is cracked in half looks to be the Diecimila's reverse protection diode. It is there to protect the main circuits from the power supply being connected backwards. My guess is you must have applied a reverse voltage for a good amount of time before that diode got to that point. I can't tell you what kind of other damage you did, but I'm fairly sure that is the reverse protection diode. I'm surprised it's working at all now, at least from external supplies. USB power should still work.

That is quite a spectacular component failure you got there.

Wait for confirmation by someone else before taking this post for anything.
9  Forum 2005-2010 (read only) / Troubleshooting / Re: using arduino diecimila with a 9v battery on: May 04, 2009, 07:16:26 am
I quoted all that stuff from the FAQ, but I took "nothing happened once I plugged in the battery." as the power not even coming on. I guess he'll have to clarify.
10  Forum 2005-2010 (read only) / Troubleshooting / Re: using arduino diecimila with a 9v battery on: May 04, 2009, 05:25:53 am
It should just work...

9V battery > DC power jack (using adapter) OR wires to GND and VIN.

The Arduino Diecimila can be powered via the USB connection or with an external power supply. The power source is selected by the PWR_SEL jumper: to power the board from the USB connection, place it on the two pins closest to the USB connector, for an external power supply, the two pins closest to the external power jack.

External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector. A low dropout regulator provides improved energy efficiency.

The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.

The power pins are as follows:

•VIN. The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.

•5V. The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply.

•3V3. A 3.3 volt supply generated by the on-board FTDI chip. Maximum current draw is 50 mA.

•GND. Ground pins.

Because the RX pin is unconnected, the bootloader on the board may be seeing garbage data coming in, meaning that it never times out and starts your sketch. Try tying the RX pin to ground with a 10K resistor (or connecting it to the TX pin).
11  Forum 2005-2010 (read only) / Troubleshooting / Re: Wires don't stay in on: April 30, 2009, 11:12:42 pm
use heavier guage wire.

If you're cheap buy 22 or so guage stranded wire and pretin the ends generously. They'll eventually wear out, though.

Another option: use the same wire and strip maybe 2/3" off and fold it backward so there is 1/3" and pretin it. This will make the ends thicker and stronger.

Those jumper wires are an option though.

These are just random ideas that might work.
12  Forum 2005-2010 (read only) / Troubleshooting / Re: 16x2 Not Displaying Right on: April 02, 2009, 12:17:42 pm
I also grabbed one of those boards from , it makes me feel so lazy, but it sure gets the job done. It's ridiculously easy to use, and its most likely compatible with your LCD. I'd consider it if you can't solve your problem.
13  Forum 2005-2010 (read only) / Development / Re: Mini Megadunio on: May 26, 2009, 03:42:27 pm
ah yes, i severly miscounted, still a lot of pins
14  Forum 2005-2010 (read only) / Development / Re: Mini Megadunio on: May 24, 2009, 11:53:19 pm
96 pins, christ.
15  Forum 2005-2010 (read only) / Development / Re: Made my protoype with Arduino. How do I make more? on: May 05, 2009, 06:46:34 pm
mdowning, I think the main function of his design is based around using the USB port as a serial port to the computer, so I think he needs a breakout board for every one of them. I may be wrong.


I took this picture of some of the crap I have to give you ideas:

Yellow = Cost Prohibitive, yet beautiful Arduino Nano solution
Red = DC Boarduino, mounts directly into breadboards and protoboards. (so does the nano, obviously)
Green = BBB, use male and female headers or solder directly to protoboard with male headers.
Blue = Custom breadboarded Arduino. Note the diode and resistor near the FTDI header don't do anything, they were going to get lost on my workspace so I put them there.
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