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841  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Dimming with max7219 on: April 25, 2008, 03:07:09 pm
Hi,
Dim some Leds or all 256 leds?
You should probably forget about the MAX7219 anyway, because it was never intended to be used with RGB-Leds.
There are some people on this forum who made it work with RGB Led's but not without problems (flickers) on updates.

What sort of display are you building? There are several ways to drive Led's, but none of them is cheap if we talk about controlling the brightness of each individual Led...

Eberhard

842  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Dimming with max7219 on: April 25, 2008, 01:45:59 am
Hi melka,

No, won't work with the max7219/7221.
The resistor sets the maximum brightness of the leds (or rather the maximum current through the Leds). The brightness of the whole matrix can be controlled by software, but not an individual Led.

Your pseudocode uses software-multiplexing, but the MAX7221 already multiplexes in hardware. The Led will surly flicker wildly...

Eberhard
843  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Can I control multiple arduinos together? on: April 26, 2008, 10:57:09 am
Yes, for : you can add several Arduinos to your computer using one or more hubs!

I have never used Processing so I can't tell how it handles the devices.
Eberhard


844  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Issue with my Multimeter on: April 15, 2008, 04:05:00 am
Hi,
you might want to try Google for "measuring current" to get the basic idea.

Answer to 4)
You short-circuit the battery with the meter. (See above)
Answer to 5)
when measuring AC-current the DC-part of the current of the signal is blocked. So you probably measure some ripple on the power-supply here. Switching to AC-current in DC-circuits is wrong, but doesn't break anything.

Fuse is OK, there is no need to replace it.

Eberhard



845  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Larger Arduino projects on: April 10, 2008, 02:13:49 pm
Quote
Some costs (in 100s) for an LIS302DL ushield that plugs into a bigger shield:
LIS302DL: $7.59
1sq in PCB: $0.64
Misc passives: $0.30 (two or three caps )
4 pin header: $0.07
----
$8.60

Even assuming Ladyada's 'double part cost' pricing system, we're looking $17.20US (10.90 Euro).
This is not a non profit thing, or is it?

So add : phone calls, postage, package, taxes, customs
the list  is long and did not include a tiny bit of profit yet!

BTW : Things that sell in the states for 100$ usully sell for 100Euro over here :-(

And as I said I'll buy one maybe even more as soon as they are released...

Eberhard
846  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Larger Arduino projects on: April 10, 2008, 01:52:45 pm
Hi,
Quote
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Hi,
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The wiichuck is nice to do testing and prototyping, but it doesn't have a format that can be installed in a robot or in some project.  How do you attach it?  I know it is fairly priced and it is easy to play with, but the format is what makes it impractical for use in projects.
Look at these pictures  http://www.wiire.org/Wii/nunchuk
thats what's when all the palstic is gone...

Eberhard
In that case, if someone makes the investment to manufacture plain LIS302DL boards and can sell them at similar prices as the nunchuk, don't you think it is a better solution?  Wasting all those resources (extra plastic enclosing, packaging, etc) makes no sense in a green world that we all envision.
I would buy one! Absolutely! But I just don't think anybody around here can produce this board for a competitve price.

Here in germany the Nunchuck is ~ 20 Euro. I would throw in another 10 Euros because I appreciate the whole idea of open-source hardware. So I would be willing to spend 30 Euros for the 3-axis accelerator shield.

But just this morning I stumbled across the Ethernet-Shield-Kit from adafruit and it sold for 15 Euros (without  the Xport). If the LIS302DL boards go to similar prices (15 Euro + the chip) I think you are already past the maximum limit.

Not mentioned yet : postage+package ; Board is not assembled? I can't solder SMDs, I'm too old for that  :-X

I find everything in this thread very promising, but its really hard to beat the nunchuck ...
Eberhard
847  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Larger Arduino projects on: April 10, 2008, 12:47:06 pm
Hi,
Quote
The wiichuck is nice to do testing and prototyping, but it doesn't have a format that can be installed in a robot or in some project.  How do you attach it?  I know it is fairly priced and it is easy to play with, but the format is what makes it impractical for use in projects.
Look at these pictures  http://www.wiire.org/Wii/nunchuk
thats what's when all the palstic is gone...

Eberhard
848  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Getting a 5V supply from the board? on: April 08, 2008, 02:51:43 am
Hi,
Quote
Well, I did say I've only just started this stuff....sorry about the unnecessary question!  
things like that happend to me a lot of times. Doing correct measurings is one of the hardest things in electronics. Whenever I get a strange reading on my meter I examine my measuring setup first. Usually that solves about 80% of the problems already ;-)

Eberhard

849  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Getting a 5V supply from the board? on: April 08, 2008, 01:28:37 am
Hi,
there should 5V exactly where you expect them between the sockets labeled 5V and GND on the "Power" section.  
That's the theory at least. So you either doing something wrong while measuring (wires to your meter don't have good contact inside the socket on the arduino maybe) or there is a hardware problem.

If you got steady hands maybe you could try to measure the voltage between the pins from the backside. But be careful not to short-circuit the power supply when trying.

Eberhard
850  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Controlling sounds volume on: April 02, 2008, 03:34:30 am
Hi,
Quote
why 500hz? I haven't used the IDE, but the chip itself can do 62.5KHz with 8 bits of precision.
Its just that way with the arduino. If you use the Arduino analogWrite() function the PWM is at 500Hz. This is not a question of using the IDE or an external Editor, its in the libraries.
(Could be changed, but thats off topic)

Quote
Oh, and that circuit limits by cutting volume down when peaks are detected. It works in a completely different way to a couple of diodes. If you supply a constant current to the led, you get constant attenuation to all parts of a signal.
Diode-Limiters are usually sold under the name FuzzBox, MegaDistortion at shops for guitar gear.

Its true that using a combination of Led/LDR for volume-control is common practice (for instance the old-school "Tremolo" guitar-effect works that way), but just not adviseable with the PWM-noise coming  from the Arduino. I can't recommend that for a good quality audio solution.
Eberhard
851  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Controlling sounds volume on: April 02, 2008, 02:28:42 am
Hi,

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Umm can't control volume with a circuit that controls volume?
http://en.wikipedia.org/wiki/Limiter

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what planet are you from? just hook the led to pwm with an rc filter instead of the peak detector...
PWM frequency on the arduino is at 500Hz. You will have a really hard time filtering this nice square-wave noise from you audio signal.

Eberhard



852  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Controlling sounds volume on: April 02, 2008, 02:06:41 am
Hi,
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I have a different question about controlling volume.  I'm working on a video/sound installation and I'm using a sonic rangefinder to input the distance a person is from the sensor.  What I'm attempting to do is have the volume for the video that is playing to get louder as they get closer.
...
You might be interested in this: http://www.arduino.cc/en/Tutorial/SPIDigitalPot
That basic idea is to put a small audio-preamp that is controlled by on of these digital pots, between the MAC and the power Amp.

I could not find a complete circuit but you might want to try these keywords on Google
"spi controlled potentiometer preamp"
That should give you a few hints.

Eberhard
853  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Controlling sounds volume on: April 02, 2008, 01:51:09 am
Hi,
Quote
See http://sound.westhost.com/project53.htm which has a great way to control volume from one of the arduino's PWM outputs smiley-wink
The circuit on this page is a volume-limiter. It is used to protect to your speakers from overloading (or in other circumstances) for changing the dynamic of an electric guitar. You can't control the volume with this circuit.

Eberhard
854  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduino contest!? on: March 27, 2008, 04:09:27 am
Hi,
Quote
Good idea!

I'd like to see an Arduino controlled LED 7 Segment Display clock.
Not really a clock but ...



(code is here http://www.arduino.cc/playground/Main/LedControl)

Eberhard
855  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: eaaasy question.. on: March 28, 2008, 04:07:03 am
Hi w,
here is a link for a page full of midi schematics http://home.concepts-ict.nl/~nctnico/midi.htm
On one of these pages it says that a midi-interface  works by switching a current of ~5mA on and of.
(Switching currents as opposed to switching a Voltage-level is used in areas where there is a lot of (electronic) noise from the outside, like when a band is playing on stage.)

So the 220Ohms is there to limit the current to (roughly) 5 mA. As there is usually an Led on the other end of the Midi-Controler-circuit, I think a current from 3-20mA would be acceptable.

And here is the "official" midi-schematic
http://www.midi.org/about-midi/electrical.shtml
I guess it's the midi-out section you are interested in. This has actually two resitors (plus another one on the midi-in receiver side).

But using only one resistor should be fine.

Eberhard
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