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1306  Community / Exhibition / Gallery / Re: Awesome LED glasses project on: November 21, 2012, 11:57:53 pm
So did you accidentally stumble on this as you've claimed or is it the fact that you're personal friends with the project owner that lead you to this project?

Just curious. Because the latter would be pretty amazing.
1307  Using Arduino / Project Guidance / Re: Need an air flow generating unit for automatic wind instrument on: November 21, 2012, 02:00:18 am
Wouldn't a decent sized centrifugal fan work for this? I thought recorders don't have all that much air resistance. In fact wikipedia mentions pipe organs use pressures in the order of 0.1 psi which equates to roughly 2.75 inch-aqua. I'm pretty sure even small centrifugal fans that were used in computers years ago can create static pressures higher than that.

The fan needs to be an impeller type and not squirrel cage. Even a ~250W furnace blower (which are squirrel cage) don't do anything for static pressure (DAMHIKT). You could use something like a vacuum cleaner motor or pool toy / mattress inflator but the problem is that they're too damn noisy.

To your question on CFM for a refrigerator compressor it looks like they're in the 1 CFM  (28 liter/minute) range and capable of ~100 PSI. Surprising number of examples of "homemade air compressors" on Youtube using these pumps. They are oil piston compressors just like typical large compressors so I suppose it does make sense.
1308  Using Arduino / Project Guidance / Re: Adruino monitored wind turbine on: November 20, 2012, 11:29:53 pm
Any analog pin is fine for the voltage divider -- make sure the pin will never see more than 5V.

It's not at all clear what you mean by a "dump resistor". If you're referring to burning off power from the wind turbine when your batteries are full, then that resistance should be between the two wires of your generator (assuming a DC or single phase generator) and switched on and off with a mosfet or relay. A 1.7Mohm resistor is much too high for this, but unless you can provide more details as to the peak voltage and amperage of your wind turbine it's impossible to make a suggestion.
1309  Using Arduino / Project Guidance / Re: LED Gurus? on: November 20, 2012, 11:19:03 pm
Read the battery; it should state a "mah" (milli amp hour) rating.

For alkaline batteries, a 9V battery has around 550mah meaning it can supply 500 milliamps (.5 amps) of current for an hour (or 250 milliamps for 2 hours, etc.). An AA battery is around 2000mah.
1310  Using Arduino / Project Guidance / Re: Need an air flow generating unit for automatic wind instrument on: November 20, 2012, 02:48:37 am
Here is a thread that suggests 0-10 psi is the normal human production playing the flute.

2.3 PSI (120 mm Hg) is normal blood pressure and about the best that a fit person can blow in short bursts. 3.5 PSI (180 mm Hg) is dying. The 6 PSI stated by your thread sounds remarkably high.

To the OP's question, the best suggestion I can think of for an inexpensive, quiet pump would be the compressor from a refrigerator. Google will turn up a few results on how woodworkers convert them for use as vacuum presses.
1311  General Category / General Discussion / Re: Xbee communication on: November 18, 2012, 03:13:40 pm
1312  General Category / General Discussion / Re: 3D printer question on: November 18, 2012, 03:12:05 pm
Kinda to add onto what cr0sh is saying, when I built my scrap CNC mill a few years back and I know I certainly underestimated the effort required. You spend so much time with CAD and setting the machine up that it's hard to get things done. First time never comes out right. Unless you're making a lot of parts "production" style it's always easier to make the part manually.

$3500 would buy a pretty nice metal lathe and mill. Maybe you can't sculpt a Yoda head but I can accept that.
1313  Using Arduino / Motors, Mechanics, and Power / Re: Interfacing Arduino with Pololu JRK21v3 help please! on: November 16, 2012, 09:26:19 pm
mySerial.println("11, 700");

That's eight bytes. 1/1/,/ /7/0/0 and a carriage return, or 0x31, 0x31, 0x2C, 0x20, 0x37, 0x30, 0x30, 0x0A which are the hexadecimal values for those ascii characters.
You probably want:


That would be three bytes, 0x0B, 0x02, 0xBC (although I'm not suggesting that that is a valid command for the JRK -- I have no idea). Don't forget that "println" adds a carriage return character at the end of the string as opposed to "print" which does not.
1314  Topics / Product Design / Re: PCB Nets on: November 15, 2012, 11:16:56 pm
No problem. Polygon named GND is the secret.
...and clicking the Ratsnest icon to get it to show the flooded areas.
1315  Using Arduino / Motors, Mechanics, and Power / Re: Stepper overheating on: November 15, 2012, 11:07:50 pm
The only reason you would drive the motor over its 6V rating (which will result in its 1.2A limit) is if you want more speed from the motor.

If you do drive it over its 6V rating them you must prevent it from passing its 1.2A limit. You can do this with a "chopper" driver or by adding high wattage resistors on the wires to the coils of the motor.

Take note that the chips on your Adafruit board are limited to 1.2A. If you have not blown the chips already then it will happen soon. is a very popular driver and has current limiting capability. Your stepper has 6 wires so it can be driven in a bipolar mode as this driver requires.
1316  Using Arduino / Project Guidance / Re: Vibrating motor musical instruent help on: November 15, 2012, 10:49:12 pm
If you had some kind of cushion between the motor and your vibrating surface you could press the motor against the surface for more volume?

Second idea, attach the vibrating motor to a servo arm and the servo to the vibrating surface. When the servo arm is parallel to the surface the amplitude of the vibration should be less than when the servo arm is perpendicular to the surface.
1317  Using Arduino / Project Guidance / Re: Read battery voltage remotely? on: November 15, 2012, 10:42:10 pm
Any Arduino will do (Uno compatible / ATMega328 chip) and then you also need an ethernet shield, preferably one with a Wiznet W5100 chip. Combined the two should be less than $40. You can find lots of examples of how to serve a web page if you do a little searching.

To read your voltage you just need a couple resistors. If you have any interest in electronics you should buy an assortment pack of resistors, but if you just want to do this one project then a 10K potentiometer or seven 2200 ohm resistors would work (when combined to form a 8800 and 6600 ohm resistance). for an example.
1318  Using Arduino / Project Guidance / Re: Everybody hates Newbies...BUT on: November 14, 2012, 06:46:51 pm shows how to use a button. shows how to use an LED.

1319  Using Arduino / Project Guidance / Re: 38khz Led Reciever Autonomous Robot on: November 14, 2012, 06:44:24 pm
void IR38Write() {
  for(int i = 0; i <= 5; i++) {
    digitalWrite(IRledPin, HIGH);
    digitalWrite(IRledPin, LOW);

It's only a series of 5 blinks; the IR receiver requires 6 minimum. The "letsmakerobots" example code -- which you should probably follow -- uses 384.
1320  Using Arduino / Project Guidance / Re: Want to emulate a rotary encoder, have a couple of questions. on: November 14, 2012, 06:19:25 pm
You should look into finding out if your car sends its steering wheel controls (volume up, etc.) through the car's OBD-II system.
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