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16  Using Arduino / Project Guidance / Re: PWM signal over long(ish) distances? on: September 18, 2014, 12:40:45 pm
It isn't so much about the wire size, as it is shielding. Send it over twisted pair with one of the pair ground, and you might be able to do that. It depends on the environment and how noisy it is, and how close the wire runs to other wires that may be carrying a lot of RFI.

Keep it away from cables running to stage lights. Cross other wires at right angles and don't run parallel to them, or at least keep it away from the other wires.

Best way to find out is to try.
17  Using Arduino / Project Guidance / Re: avoiding delay on: September 18, 2014, 12:06:20 pm
This thread should probably be a sticky post:

http://forum.arduino.cc/index.php?topic=223286.0
18  Using Arduino / General Electronics / Re: Not all breadboards created equal on: September 18, 2014, 11:43:01 am
That sounds fraught with problems.
19  Using Arduino / Project Guidance / Re: Putting a display on MAX038 on: September 18, 2014, 11:42:24 am
So you have an Op Amp connected to pin 10, IIN? You might be especially vigilant about checking out that part of the circuit.

Are you doing something like this?


http://www.armory.com/~rstevew/Public/Ccts/MAX038FunctionGenerator.htm

You might also try building a very simple circuit on a protoboard and plugging the MAX038 into it for testing. Something like this:

20  Using Arduino / Project Guidance / Re: Circuit to make Arduino detect static charge from carpet on: September 18, 2014, 11:05:41 am
Hall effect sensors read magnetic fields, not electric fields.

Noncontact electrometer - the Fieldmill
This was in Scientific American, in a column called "The Amateur Scientist".

It can measure electric fields at great distances, measured in V/m (volts per meter). Measure how far the charged object is away, and you can calculate the voltage. So you can measure the charge on objects like clouds, or closer objects.

http://www.precisionstrobe.com/jc/fieldmill/fieldmill.html

More information on non-contact surface voltmeters:

http://www.trekinc.com/pdf/3002-field-voltmeter.PDF

Loads more information:

http://scholar.google.com/scholar?q=electrostatic+surface+voltmeter+noncontact&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ei=QMaGU7qUOsi7oQSniIKQBQ&ved=0CDgQgQMwAA
21  Using Arduino / Project Guidance / Re: Putting a display on MAX038 on: September 18, 2014, 11:01:40 am
Check and doublecheck your wiring. Remove the MAX038 from the socket and measure voltage on that pin. What is it?

Can you post a schematic of what you have built?

If the wiring checks out and voltages are as expected with the chip removed, then I'd say you have a bad chip.
22  Using Arduino / General Electronics / Re: Not all breadboards created equal on: September 18, 2014, 10:24:24 am
I've measured between 2pF and 15pF between adjacent rows on a variety of protoboards. I'm sure it depends on the geometry and the dielectric constant of the plastic.
23  Using Arduino / Motors, Mechanics, and Power / Re: Reading DC rms/average voltage from a pwm signal on: September 18, 2014, 10:15:50 am
Frack! Brain fart.

For a square wave, Vavg and Vrms are _NOT_ the same thing. Calculating average voltage is as simple as duty cycle times peak voltage. So 5V pulses at 50% dutycycle is 0.50*5 = 2.5Vavg. Vavg = Vpk*dutycycle/255

However, power is equal to V^2/R, and Vrms specifically is the equivalent DC voltage that would cause the same power to be consumed. So for 5V pulses at 50% dutycycle:

5V^2/1 = 25W
2.5V^2/1 = 6.25W
0.50*5V^2/1 = 12.5W  Obviously not the same as 2.5V

(dutycycle/255)*(Vpk^2)/R = P = Vrms^2/R
(dutycycle/255)*(Vpk^2)/R = Vrms^2/R
(dutycycle/255)*(Vpk^2) = Vrms^2  cancel R from both sides
sqrt(%*Vpk^2) = Vrms  square root of both sides
Assuming Vpk is 5V:
Vrms = ((dutycycle/255)*(5^2))^0.5 
Vrms = 5*(dutycycle/255)^0.5   separate out the square root of 5 squared

Someone correct me if I'm wrong.

I cross checked my answer with this website:
http://masteringelectronicsdesign.com/how-to-derive-the-rms-value-of-pulse-and-square-waveforms/

24  Using Arduino / Sensors / Re: Non-contact liquid sensors on: September 18, 2014, 09:55:21 am
My guess would be capacitive. That is a bit of foam rubber metal coated EMI gasket.
25  Using Arduino / Sensors / Re: Detect 0.1mm object on: September 18, 2014, 09:51:31 am
I wonder if you could use an optical mouse as a close-up camera, suspended so the objects pass just below the mouse. But how is the positional repeatability of the object on the belt?

An optical or laser mouse is really just a tiny, low resolution camera. I don't know if it would have enough resolution for this. Side lighting could help pick out the tabs.

http://www.wildcircuits.com/2013/03/optical-mouse-hacking.html

http://hackaday.com/2014/01/14/your-mouse-is-a-terrible-webcam/

http://frenki.net/2013/12/convert-optical-mouse-into-arduino-web-camera/
26  Using Arduino / Sensors / Re: Detect 0.1mm object on: September 18, 2014, 09:43:18 am
If this is stable enough, I think I'd set a laser to just hit the 0.6mm tabs sticking up, along with another sensor to detect that the object is in the beam so it knows when one without tabs is there.

If the laser beam is too wide, just shot it through a pinhole in a sheet of heavy duty aluminum foil.
27  Using Arduino / Motors, Mechanics, and Power / Re: Reading DC rms/average voltage from a pwm signal on: September 17, 2014, 06:53:10 pm
Actually, if driven by a very low resistance like a saturated MOSFET, that measure of RMS voltage -will- be accurate.

However, the power will not be. And using an RC lowpass filter will only give you the average/RMS voltage for a square wave, not the power.

For the power, you need to know the current. If it is a resistive load, it is a doddle as you now the voltage and so the power is simply V^2 / R.

If it is a capacitive or inductive load, you are going to need a series current sense resistor and a fast ADC to capture a lot of samples during a cycle.
28  Using Arduino / Sensors / Re: Need hardware suggestions for outdoor proximity sensor project on: September 17, 2014, 06:49:40 pm
If you use an IR LED and phototransistor, you'll have a beam that someone has to break to set it off that can work from a fairly long range.

http://www.circuitstoday.com/infrared-motion-detector-circuit

Both the LED and phototransistor are parallel to each other, pointed at a retroreflector (like a reflector from a bicycle).



http://www.amazon.com/Seco-Larm-Enforcer-Reflective-Sensor-Reflector/dp/B008G6NLGK
29  Using Arduino / Project Guidance / Re: What sensor do I need? on: September 17, 2014, 06:44:39 pm
One way is to shine a light across the space into a retroreflector (ie, a bicycle reflector) and back to a phototransistor. Lens on both the light source and phototransistor to make it a tight beam and tight pickup.

The reflector reflects the light almost entirely back at the source, so put the source (LED) and detector right next to each other.



Use IR with shield tubes with small holes in them. Pulse the source and filter what is received to make it nearly insensitive to interference.



http://www.circuitstoday.com/infrared-motion-detector-circuit
30  Using Arduino / Project Guidance / Re: LEDs say yes, but Input pins say nothing, or too many things?! on: September 17, 2014, 06:37:07 pm
Measure. Measure. Measure.
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