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1306  Using Arduino / Motors, Mechanics, and Power / Re: Help with stepper motors? on: March 02, 2013, 02:01:57 am
Pinouts for the SN754410 are the same as the L293. Given a choice between the two the SN754410 is preferred as it has slightly higher power ratings.

In my experience the biggest problem with these chips is having sufficient/clean power. If your supply is noisy or cheap you'll have problems.
1307  Using Arduino / Sensors / Re: IR receiver based distance sensor on: March 01, 2013, 11:53:54 am
It seems the IR receiver circuitry kind of adapts or something... I guess that's caused by the circuitry inside the IR receiver.

Yes, IR receivers automatically adjust their sensitivity. If you look at your datasheet it will refer to this as "automatic gain control" or "AGC" in the block diagram. You can compare this to Vishay part TSSP4038 which does not adjust its sensitivity (it's "fixed gain").

TSSP4P38 is what you're looking for if you want to do distance detection. This is $.95 at Digikey.

See also for a nice matrix list of different IR receiver types.
1308  Using Arduino / Motors, Mechanics, and Power / Re: Easy driver vs StepStick A4988 on: March 01, 2013, 05:10:59 am
I believe you always want to use one driver per stepper. I've never seen it done or tried it otherwise; I'd expect that you'd get unbalanced power if you connected multiple steppers to one driver.

The A4988 has one extra level of microstepping available (if you wanted it). Otherwise, with respect to connecting it up and coding for it, everything is the same.
1309  Development / Other Hardware Development / Re: My first pcb on: March 01, 2013, 05:03:40 am
Another thing I need to learn from you is in how you hook up your capacitors - am I reading your schematic correctly, in that C8 is only connected on one leg? Is this what you mean by saying ' You can always leave the spaces unpopulated', which I didn't really grasp?

He has a ground plane which isn't visible. The side that appears to be unconnected is actually connected to GND in a flood fill.

With respect to "leaving spaces unpopulated" I'm referring to not adding the part in the final circuit. For example, if you just wanted to run your 328 at 8MHz using the internal oscillator then you'd leave the spaces for the crystal and capacitors "unpopulated".
1310  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.
1311  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
1312  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!
1313  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.
1314  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.
1315  Using Arduino / LEDs and Multiplexing / Re: Led RGB with just two wires on: February 26, 2013, 05:15:41 pm
Example at
1316  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.
1317  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.
1318  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.
1319  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.
1320  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.
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