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1066  Using Arduino / General Electronics / Re: LED response time on: January 16, 2014, 04:39:45 am
How fast is the shutter?
1067  Using Arduino / Installation & Troubleshooting / Re: Freeduino Programming Problems on: January 15, 2014, 08:30:14 pm
Let us know if that solved your problem.
1068  Using Arduino / Installation & Troubleshooting / Re: avrdude: stk500_getsync(): not in sync: resp=0x00 on: January 15, 2014, 08:27:28 pm
Developed your own board... no schematic, no information on the bootloader. Did you write your own bootloader, or use an existing one? Which one? How did you program in the bootloader?
1069  Using Arduino / Installation & Troubleshooting / Re: OLD STORY: avrdude: stk500_getsync(): not in sync: resp=0x00 on: January 15, 2014, 08:24:54 pm
I had the same problem.

Presumed cause: Counterfeit FTDI chip on compatible Arduino Nano V3.0. Driver works fine, but maker of FTDI chip creates an update that prevents the counterfeit chip from working either purposely or incidentally.

So mine worked until I downloaded an update to the Arduino software, coincidentally while installing new Teensy 3.0 drivers.

I downgraded the FTDI drivers and now both work.

http://forum.arduino.cc/index.php?topic=198681.msg1477473#msg1477473
1070  Using Arduino / General Electronics / Re: LED response time on: January 15, 2014, 04:23:51 pm
True. An LED should be able to blink on and off a lot faster than 10kHz.

I wonder how using a digital camera will affect this. I would think as long as things are bright enough that shutter speed is a far bit faster than 1/2 the time between LED changes, it would turn out OK.

So the idea is to have a row of LEDs counting up or down in binary?
1071  Using Arduino / General Electronics / Re: LED response time on: January 15, 2014, 01:18:17 pm
And how you drive it will affect the response time, limited by other factors of the LED.
1072  Using Arduino / Project Guidance / Re: Reverse engineering LCD (Excalibur plug and play poker) on: January 15, 2014, 12:10:20 pm
I agree about not spending time on this, or at least not much.

And I've got four large screen color TFT touchscreen cell phones I'd love to reverse engineer... but when I think about all the time I'll spend, $30 for a touchscreen 3.2 inch 320x240 screen doesn't seem so bad.
1073  Community / Bar Sport / Re: Big Picture Question - Arduino as a sort of "computer" ? on: January 15, 2014, 12:05:57 pm
The Commodore 64 was only a 1MHz CPU, although there was no GUI. It was a bit like a multiple CPU, however, as not only was there a 6502 in the C64, each floppy drive had its own 6502. And there was GEOS, a crude (by today's standards) GUI.

Certainly something like the Raspberry Pi makes it a lot simpler as it has things like HDMI video and an SD card reader built-in already. And people -are- building Linux computers using them.
1074  Using Arduino / General Electronics / Re: LED response time on: January 15, 2014, 12:00:51 pm
http://zone.ni.com/devzone/cda/ph/p/id/130

Quote
BW =  = 1/ (9.11)

This yields a very important principle: An LED's modulation bandwidth is limited by the recombination lifetime of the charge carriers. The physics governing this result is as follows: Suppose you excite an electron at the conduction band. It takes  ns for this electron to fall to the valence band and recombine. During this interval you cannot change its status, so that if you turn off the forward current, you must wait  ns until radiation will actually cease. This  ns interval is necessary to allow a charge carrier to reach its destination. In other words, you cannot stop an excited electron that is on its way from the conduction band to the valence band. Thus, lifetime puts a fundamental limit on the modulation bandwidth of an LED. (You can repeat this reasoning using a p-n junction model: While an electron is moving through an active region, you cannot stop it; that is, you cannot change its status until this electron recombines.)
Table 9.2 Typical characteristics of LEDs

Active Material   Type   Radiating wavelength
 (nm)   Spectral
width
 (nm)   Output power into fiber (µW)   Forward current (mA)   Rise/fall time (ns)
AIGaAs   SLED   660   20   190–1350   20(min)   13/10
ELED   850   35–65   10–80   60–100   2/2–6.5/6.5
GaAs   SLED   850   40   80–140   100   —
ELED   850   35   10–32   100   6.5/6.5
InGaAsP   SLED   1300   110   10–50   100   3/3
ELED   1300   25   10–150   30–100   1.5/2.5
ELED   1550   40–70   1000–7500   200–500   0.4/0.4–12/12

Source: Lightwave 1999 Worldwide Directory of Fiber-Optic Communications Products and Services, March 31, 1999, pp. 58-61.
This is why LEDs are restricted by bandwidth in the range of hundreds of MHz. Such restrictions determine their applications in local area and other low-bandwidth networks.

Power-bandwidth product is another important characteristic of an LED. It appears that the product of an LED's optical output power and its modulation bandwidth is constant:


BW  P = constant   (9.12)

In other words, you can increase an LED's bandwidth but only at the expense of its output power. Alternatively, you can increase output power but then bandwidth decreases.


Driving LED in a Nanosecond Regime by a Fast Operational Amplifier
http://arxiv.org/ftp/arxiv/papers/1011/1011.1954.pdf

Quote
Abstract
 
It is widely believed that the generation of high speed optical signals is
not the job for an LED. However this work is done to show that there are
techniques which can be used to produce nanosecond square pulses from
a diode. Rise and fall times of a typical 10ns long signal were 1-2 ns and
the intensity of the emission could be controlled by the supply voltage.
The wavelength of the radiation was 472 nm, which is blue in colour, but
any longer or even shorter wavelengths can similarly be used. The
consistency of the experiment and its theoretical model was analysed by
computer simulations using OrCAD and PSPICE.
1075  Community / Bar Sport / Re: whats with the attitude on: January 14, 2014, 03:26:25 pm
I've seen name-calling and been called names, but not by any moderators.
1076  Using Arduino / General Electronics / Re: divede analog signal between 2 analog inputs for getting high resolution on: January 14, 2014, 03:24:18 pm
xzarth: If you "split" 0-10V, when the signal is above 5V, the lower is always 1023. When the signal is below 5V, the upper is always 0.

All you've really done is add one more bit of information.

Oversampling, or a higher resolution ADC with a lot of care put into low noise, low distortion, etc. Look up ENOB.
1077  Using Arduino / General Electronics / Re: Reducing the time period a motion sensor is on from 5 secs to 0.5 secs on: January 14, 2014, 11:00:36 am
Obviously the 555 timer is not obsolete, there are at least a half-dozen manufacturers making different kinds of them.

Good point about requiring a low voltage. I'll have a think.
1078  Using Arduino / General Electronics / Re: Need some help with arduino wiring on: January 14, 2014, 10:58:20 am
I'm not explaining this adequately.

The relay coil draws 90mA at 5V. But the Arduino pin is rated at a maximum of 40mA source or sink out of a digital pin. This is bad. This is bad for the microcontroller on the Arduino board. You either need to find a relay that only requires 30mA at 5V, or use a buffer transistor like a 2N3904.


As for the relay contacts, one with the contacts rated at 1A @ 120Vac is fine to run a 3W pump like that one. It is NOT overkill, the contacts -must- be rated at a lot more than the pump requires. The pump will draw more current when it starts, and relay contacts wear faster if you run them at or very near their maximum rated current.
1079  Using Arduino / General Electronics / Re: divede analog signal between 2 analog inputs for getting high resolution on: January 14, 2014, 09:55:57 am
There are some tricks using oversampling to get greater resolution, but the Arduino board is handicapped by not being designed with analog capture in mind, and the Atmel chip isn't completely separated internally between the analog and digital sections.

I concur with PaulS, use an external ADC. It is even more important with greater bit depth to pay attention to layout, power supply decoupling, noise, distortion, etc. There is something called ENOB, Effective Number Of Bits. Basically, the lowest bit or two is garbage because of the problems of noise, quantization error, distortion, etc.

What kind of resolution do you need? I mean really need. 24 bits is unrealistic without a -lot- of work. And at what speed?

http://forum.arduino.cc/index.php?topic=208351.msg1532892#msg1532892

The 32 bit ARM based Teensy 3 ($20) has a 16 bit ADC. The Teensy 3.1, current version, has lots of improvements over the 3.0 and the Due, including two ADC converters and 5V tolerant inputs (the Due and Teensy 3/3.1 are 3.3V chips).

http://www.pjrc.com/teensy/teensy31.html
1080  Using Arduino / General Electronics / Re: Need some help with arduino wiring on: January 13, 2014, 03:02:38 pm
That circuit isn't going to last long on a 9V battery. Why not just build a small power supply into it? Seems ridiculous to have something that plugs into a wall outlet require a battery to run it. I doubt that you'd get more than a few days from this.
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