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1291  Using Arduino / Project Guidance / Re: ARDUINO as a RPM limiter on: February 12, 2013, 11:59:09 am
I would be interested in this for an automotive application any way to get over the overheating issue?

You reduce the amount of time that current is flowing through the coil (the "dwell" time). It should only be energized for a very short period before you switch off the current / create the spark. Just take a close look at your distributor and you'll see the the breaker points are only closed momentarily.

There are special purpose IGBTs/mosfets designed for this type of high voltage current switching; a dig around Fairchild Semi's site will list a number of them. Or use the google, etc.
1292  Using Arduino / Sensors / Re: Calculating Vehicle Position with an IMU on: February 12, 2013, 01:26:49 am
"Optical Flow Sensor" like a mouse. 3drobotics.com used to sell a nice breakout with a sensor and a lens but it looks like they discontinued it. I understand the most difficult part (aside from the code) is finding an appropriate lens so you can get the floor in focus for the sensor.
1293  Using Arduino / Sensors / Re: Peizo Sensor to detect hits from a bat on: February 12, 2013, 01:15:25 am
Good link for filtering piezo signals:

http://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/f2012/asj42_gs368_ln226_awh49/asj42_gs368_ln226_awh49/index.html
1294  Using Arduino / Motors, Mechanics, and Power / Re: VFD - anyone any experiences or hints? on: February 11, 2013, 06:55:16 pm
Why not to use TRIAC, MOC and Arduino to PID control the AC motor??/
Three phase motors don't allow that type of control. The speed of their rotation is locked to the AC frequency.
1295  Using Arduino / Project Guidance / Re: ARDUINO as a RPM limiter on: February 11, 2013, 06:47:30 pm
PeterH is thinking you're using an automotive type coil that receives power from the battery. You're apparently using the type of coil that generates its charge from a magnet on the flywheel. No, there's no risk to the coil for what you're doing.

1296  Using Arduino / Motors, Mechanics, and Power / Re: Wall Wart amperage question. on: February 09, 2013, 05:38:27 pm
Depends. If you pull more amps from a wall wart than it's rated for then you should wear Depends.

Could be anything from switching off until replugged-in, blowing a fuse, or creating a fire.
1297  Using Arduino / General Electronics / Re: hooking up power supply to Arduino extendershield on: February 07, 2013, 08:17:01 pm
I see what you're saying now.

You can bring those 5V/GND wires to the 5V/GND holes on the extendershield. The extendershield then already has the traces to bring that power to the Uno.
1298  Using Arduino / Sensors / Re: Arduino Lilypad load scale. on: February 07, 2013, 03:03:45 am
You'll need a separate instrumentation amplifier for each of the load cell sensors. I don't think there's any practical method of adding the signals together to get a cumulative value. You can also multiplex the sensors but the required multiplexer chips are pretty pricy.

If you can provide more detail as to what you're using for load cells and what kind of precision you're try to achieve then you'll get better guidance on how to move forward.
1299  Using Arduino / Motors, Mechanics, and Power / Re: Controlling a ducted fan on: February 07, 2013, 02:57:27 am
Your delay of 100ms is not much of a delay to really see the motor even change speed, much less stop.

Do you have your button wired correctly between the digital pin and GND and an additional 10K resistor between the digital pin and 5V?
1300  Using Arduino / Motors, Mechanics, and Power / Re: Controlling DC voltage to a linear actuator on: February 07, 2013, 02:41:24 am
An RC servo (or this actuator with an RC interface) doesn't have a feedback for actual position. You tell it what position you want it to move to and assume that it does actually move to that point. Your speed is then determined by how quickly you move it between positions.

If you don't like assumptions at all then you can buy their version which provides the RC control AND an analog output for position feedback. It is more expensive though, and IMHO overkill in this situation. Not having feedback is the same situation you'll see with millions of CNC machines with stepper motors; you can command them to "step" but (typically) can never verify that they actually do step.

Btw, to the OP, you might be going overkill using this linear actuator to move a syringe. A medium size RC servo that you'd find in a hobby store should have plenty of power to push a syringe. A quick google search reveals examples using that method.
1301  Using Arduino / General Electronics / Re: hooking up power supply to Arduino extendershield on: February 07, 2013, 02:27:20 am
The backpack blocks the 5V/3.3V/GND holes because it's providing the 5V power; you don't need to add anything additional (while the battery is charged). If you DO want to provide external power than you can plug in a USB cable or supply 5V via the horizontal, female header pins on the backpack.

If you're asking how to provide power from one side of the extendershield to the other side -- you don't have to do anything. Those wires (traces) are already present. The row of 5V/GND/3.3V holes are just extra holes for your convenience.

Apologies if I'm misunderstanding your question.
1302  Using Arduino / General Electronics / Re: Vishay TEPT5700 - Ambient Light Sensor problem on: February 07, 2013, 02:18:09 am
The typical scheme is 5V -> 10K resistor -> analog pin -> phototransistor -> GND (a "common emitter" scheme).  This sets the pin high when it's dark and low when it's bright. I can't say I fully understand the math but it just seems to work better at typical light levels.

With your current wiring a larger resistor should give you more of a sensor swing.
1303  Using Arduino / Microcontrollers / Re: Attiny85 Invalid device signature... on: February 07, 2013, 01:42:38 am
The question is whether or not you're resetting your Uno and unloading ArduinoISP when you're trying to program the ATTiny. The capacitor you placed between reset and GND (you did that part, right?) should prevent that reset, but y'know ... it's a good idea to be certain.
1304  Using Arduino / Motors, Mechanics, and Power / Re: Controlling DC voltage to a linear actuator on: February 06, 2013, 06:07:28 pm
To adjust the voltage supplied to the actuator I assume I could use some sort of digital PWM, but I'm confused about the differences between analog and digital PWM.  Is digital PWM just a matter of switching between 0 and 5V more quickly than you would if you wanted an analog signal?  Also, given that the max DC voltage of the actuator is 12V, I was considering implanting a simple non-inverting amplifier between the Arduino and the actuator.  I'm worried about overdrawing current from the Arduino as well, so I thought that implanting the non-inverting amplifier might help with that respect, drawing current from Vcc+ (please correct me if I am mistaken).

An analog signal suggests a voltage somewhere between 0 and V+. A digital signal is 0 OR V+. With PWM you're switching between 0 and V+ at a fast rate so that the average voltage is somewhere between 0 and V+; it would be similar to flicking on and off a light switch really quickly in an attempt to make the light less bright.

To drive a DC motor bidirectionally you need an H Bridge ("Full bridge"). You can drive the motor in one direction using a transistor (or mosfet), but to drive it in both directions you would need an arrangement of four transistors to form a full H bridge.

Specifically to your Firgelli L12-S you should buy the identically priced L12-R instead. It has an RC interface and would be driven just like an RC servo -- no additional motor driver / bridge needed. Example: http://playground.arduino.cc/Learning/SingleServoExample -- but you can find many more examples with a little searching.
1305  Using Arduino / Motors, Mechanics, and Power / Re: Do I need a motor shield? on: February 06, 2013, 05:49:26 pm
So then what is the main advantage(s) of buying and using a motor shield which seems to cost a lot more than 2 H-bridges? Thanks!

The motor shield plugs right in on top of the Arduino -- it's just a convenience.

Strictly speaking the L298 on the motor shield is capable of a bit more amperage and has current sense outputs (tells you how much power your motors are using).
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