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1261  Using Arduino / Motors, Mechanics, and Power / Re: Easy driver vs StepStick A4988 on: March 01, 2013, 02:22:54 am
The A4988 is preferred; 2000ma max vs. the A3967 at 750ma. Not much difference otherwise.
1262  Development / Other Hardware Development / Re: My first pcb on: February 28, 2013, 10:20:09 pm
AVcc, Aref, and the GND pin near them are applicable to the analog inputs (that GND pin is sometimes referred to as "AGND"). The Vcc and GND on the other side of the chip are applicable to the digital inputs. In an ideal design those analog and digital GND connections would only intermingle right at the power jack. All of your analog pins would only use their AGND and be kept separate from the GND used by the digital pins. There would be three separate capacitors between AVcc and AGND, Aref and the same AGND, and Vcc and its associated GND.

As an example for why all this is, when you're blinking your LED on pin 7 and it's jumping between 5V and 0V you're causing small voltage surges/drops that can be noticeable by the analog pins. Normally the analog pins will only see slow changes in voltage around them -- which is great for stable readings -- so you don't want to introduce additional noise from your blinking LED.

You really only do most of this stuff if you're really concerned about getting the most stable analog readings possible and for most projects it doesn't matter. The official Uno doesn't even follow these rules. But, you asked, so I did my best at explaining smiley
1263  Development / Other Hardware Development / Re: My first pcb on: February 28, 2013, 12:50:12 pm
You need to post the schematic.

I'm not familiar with the program you're using here, but if possible you want to fill the board with a ground plane to take heat away from the regulator. At worst you can do it manually by just adding a lot of extra, thick traces. Also, that regulator needs capacitors (typically electrolytic) on its power in and power out lines; if you don't include them your power will be fruity. You can always leave the spaces unpopulated if you find that you don't require them -- but can't add a capacitor if you find out you need them and don't have a space available!
1264  Using Arduino / Project Guidance / Re: Controller for rc flight models like helicopters, quadcopters and tilt-rotors on: February 26, 2013, 08:47:39 pm
That KK2 board is getting pretty dated. The gyros are old school piezo and it uses an ATMega168 which is too small for the newer firmware. That's why Seeed has it on closeout.

This board uses a MPU-6050 (acc + gyro) and is compatible with MultiWii which supports pretty much any configuration you can think of.
1265  Using Arduino / General Electronics / Re: manual and smaple code for DFRobotics relay shield 2.1 on: February 26, 2013, 05:18:08 pm

Might not list your particular board but it explains the relay board genre very well.

You should anticipate that the relays will require ~100ma per relay when energized and that's why they need external power. If you look up the specs for the particular model relay (google the part number) you'll get a more definitive answer.
1266  Using Arduino / LEDs and Multiplexing / Re: Led RGB with just two wires on: February 26, 2013, 05:15:41 pm
Example at
1267  Using Arduino / Project Guidance / Re: Most accurate way to measure speed of a car on: February 26, 2013, 12:33:03 pm
Calculating speed using an accelerometer would only be accurate for a few moments off the line. The only practical way is to use GPS.

In a previous discussion someone mentioned that car manufacturers are required to configure their speedometers to never report slower-than-actual speed and that they have to be accurate to within ~10mph? I know on my car that it will report its speed ~30mph when actual speed is 20mph. YMMV (literally) if you try to use the car's speedometer.
1268  Using Arduino / General Electronics / Re: Control very high power LED on: February 26, 2013, 12:25:02 pm
50-100W IR led at 38Khz? Is this like a city-sized TV-B-Gone?.  smiley-mr-green

Linear LED current regulators (e.g. CAT4101, NUD4001) can be used in parallel for 3.5A control. Your efficiency would depend on keeping your voltage supply near your LED's Vf.
1269  Using Arduino / General Electronics / Re: can you take a look at my eagle pcb design? on: February 26, 2013, 03:17:40 am
Whoops I was totally oblivious to the fact that this is a shield.

Here's an example of a Seeed user that created a shield using their service and squeezed their pin holes right on the edge like you're doing. Worked for him so you should be OK.
1270  Using Arduino / Project Guidance / Re: Powering 1/2hp dc motor on: February 25, 2013, 07:56:14 pm
My point was that you already have variable speed in one direction. If you use a DPDT switch on the motor leads to reverse them then you can use the same variable speed to go in the other direction.
1271  Using Arduino / General Electronics / Re: can you take a look at my eagle pcb design? on: February 25, 2013, 05:41:36 pm
Seeed will allow the pads that close to the edge. The extreme would be castellated pads and that is possible with their service.

Not really a good practice though. You've got lots of board space and you should use it rather than creating physically weak areas on the edge of your board.
1272  Using Arduino / Project Guidance / Re: Powering 1/2hp dc motor on: February 25, 2013, 05:22:07 pm
Wouldn't it be a lot simpler just to throw in a DPDT switch so you can reverse the leads on the motor?
1273  Using Arduino / Motors, Mechanics, and Power / Re: Magneto interference with arduino on: February 25, 2013, 12:05:02 am
Make sure your engine has a "resistor spark plug". They should be standard on any modern engines but it's worth a doublecheck.
1274  Using Arduino / Project Guidance / Re: Measuring current from solar panel on: February 24, 2013, 11:46:40 pm
Atmel has an application note on battery charging. Starting in section 3.3 they start explaining the voltage and current measuring.

With respect to solar panels Tim Nolan's MPPT design is a must read.
1275  Using Arduino / Microcontrollers / Re: Arduino 1.0.3 - Arduino Uno and ATTiny85 problems (video included) on: February 23, 2013, 09:32:58 pm
First step should always to be sticking LEDs on pins 7/8/9. From the ArduinoISP code:

// this provides a heartbeat on pin 9, so you can tell the software is running.
uint8_t hbval=128;
int8_t hbdelta=8;
void heartbeat() {
  if (hbval > 192) hbdelta = -hbdelta;
  if (hbval < 32) hbdelta = -hbdelta;
  hbval += hbdelta;
  analogWrite(LED_HB, hbval);

Now you'll know if you've actually got the ISP sketch running. Anything else is guesswork.
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