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1276  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.
1277  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.
1278  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?
1279  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.
1280  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.
1281  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.
1282  Using Arduino / General Electronics / Re: Compatible replacement for arduino nano crystal? on: February 21, 2013, 08:35:16 am
The board pictured is not an official Nano (it's made by "funduino").

As to whether or not the eBay resonator has the same footprint is hard to say. You'd have to look up the datasheet for the eBay resonator and compare it to the footprint on your board.
1283  Using Arduino / Project Guidance / Re: Fast boat rudder system optimization on: February 21, 2013, 08:03:20 am
Seeedstudio's wiki for their flow sensor provides examples very similar to what you're trying to do with your speed sensor.
1284  Using Arduino / Motors, Mechanics, and Power / Re: 30RPM Worm Drive on: February 21, 2013, 02:27:57 am
A windshield wiper motor from the local junkyard?

Motors larger than wiper size start to ramp up in price pretty quickly. has a few lower-priced options.
1285  Using Arduino / Project Guidance / Re: Senior Project (Kickstart) on: February 21, 2013, 01:50:26 am
Does a quadracopter or UAV qualify as aerospace? Difficult to make though.

Something simpler along those lines, you could use an accelerometer to control just the ailerons on a plane to automatically bank it during turns. Ensure the center of gravity is always perpendicular to the wings.
1286  Using Arduino / Microcontrollers / Re: ATtiny85/84/2313 Reset pin clarification on: February 21, 2013, 12:31:24 am

The reset line has an internal pull-up resistor, but if the environment is noisy it can be insufficient and reset can therefore occur sporadically. Refer to datasheet for value of pull-up resistor on specific devices. Connecting the RESET so that it is possible to enter both high-voltage programming and ordinary low level reset can be achieved by applying a pull-up resistor to the RESET line. This pull-up resistor makes sure that reset does not go low unintended. The pull-up resistor can in theory be of any size, but if the Atmel AVR should be programmed from e.g. STK500/AVRISP the pull-up should not be so strong that the programmer cannot activate RESET by draw the RESET line low. The recommended pull-up resistor is 4.7k Ω or larger when using STK500 for programming. For debugWIRE to function properly, the pull-up must not be smaller than 10k Ω

Personally I've never used a pull up on my programmer boards used with ArduinoISP. If your USB ports are that noisy you've got worse problems than reset pullups.
1287  Using Arduino / Project Guidance / Re: Building gigantic Thermometer need guidance on: February 20, 2013, 09:48:06 pm
How do you define "gigantic"? What dimensions are you considering?
1288  Using Arduino / Sensors / Re: Weight Sensor for small objects on: February 20, 2013, 08:16:32 pm
If the load cell must be read by the Arduino then see for an example. It's not too hard to get right; the most problematic part is getting the gain set correctly. You'll want to use some sort of low value trimmer to get it right. Also, you'll be limited by the precision of the Arduino's A/D converter (10 bits) unless you use an external, higher precision A/D converter.

You still need the load cell of course, and extracting it from a scale like John linked is still a good idea.
1289  Using Arduino / Sensors / Re: Need ideas on tachometer using ignition on: February 20, 2013, 08:10:50 pm
Darlington's are for high-gain. Why use one to take 12V down to 5V?

You still have the noise issue. Any transistor will just amplify the noise as well.

I think Grumpy Mike's idea sounds like the best.
1290  Using Arduino / Microcontrollers / Re: Proper Handling of Reset Pin (When you have no intention of resetting) on: February 20, 2013, 06:29:26 pm
I wonder if the example you're referring to there has a cap connected not to GND for decoupling, but to the RTS pin on an FTDI connection for programming?

Just a few random examples:

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