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1  Community / Products and Services / Re: ArduinoCommander - android application to manage arduino board on: December 03, 2013, 05:22:52 pm
I'd like to share a tip that may help people having problems making the app work with their tablets. The short story is that having a USB OTG port is not enough by itself, certain configuration files should be in place as explained here:
http://tabletrepublic.com/forum/novo-7-paladin/usb-host-ip-not-supported-1136-2.html

You can create them manually, but the easier solution is to use this great app https://play.google.com/store/apps/details?id=eu.chainfire.usbhostdiagnostics&hl=en&rdid=eu.chainfire.usbhostdiagnostics. After doing this step the ArduinoCommander app now works fine with me smiley
2  Using Arduino / Displays / Re: New LiquidCrystal library - LCD library on: July 20, 2013, 07:20:27 am
thanks a lot for the replies and the awesome library!
3  Using Arduino / Displays / Re: New LiquidCrystal library - LCD library on: July 19, 2013, 01:05:50 pm
it it possible to use this library with slightly a different connection between the LCD and the PCF8574? I'm referring to this schematic https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/i2c_lcd_schematic.jpg

can this be done by hacking a certain .h or .cpp file? I'm asking this was I'm working on a pbc layout of the above circuit, and that change would simplify things a bit  smiley

edit: it's trivial after all, the documentation was clear smiley
you just use the appropriate constructor which also defines the EN, RW, RS pins
LiquidCrystal_I2C (uint8_t lcd_Addr, uint8_t En, uint8_t Rw, uint8_t Rs)
4  Using Arduino / Displays / Re: kingbright double 7-segment with dp missing (?) on: February 08, 2013, 01:57:50 pm
Production is much easier... You only build one version.. Cheaper too, the base price covers the cost of the parts for any configuration so the device is always paid for fully.

Bob

it makes sense, but isn't this unethical? I vaguely remember an article I once read which gave me the impression that such tactics are against the law, since they result in "artificially" inflated prices. I know off course, that speaking about ethics is a little odd, in times where jobs are outsourced to poorer countries so that we can enjoy lower prices for our home theaters at the expense of people having to work like slaves. Anyway, my point is that I was under the impression that such a thing is prohibited by the law.
5  Using Arduino / Displays / Re: kingbright double 7-segment with dp missing (?) on: February 05, 2013, 04:19:40 pm
thanks for the confirmation
lesson learnt, kingbright you shall not deceive me again!

by the way, I find the whole issue rather bizarre: it reminds me of the ingenious way of making business by having just one line of products, half of which have some functions disabled at the factory, so that you have to pay extra for the "advanced" model which has extra features  smiley-kitty

6  Using Arduino / Displays / kingbright double 7-segment with dp missing (?) on: February 05, 2013, 03:09:37 pm
hello, I just got a couple of kingbright dc03-11ewa
datasheet: http://www.kingbrightusa.com/images/catalog/SPEC/dc03-11ewa.pdf

but from what I see in the datasheet it's not possible to turn on the decimal point (dp) leds ?! smiley-red
well, ok, it does say 7-segment, if we count the dp that will be 8 segments, but the dp led are physically there, and I thought that the term "7-segment" includes the dp by default. I don't know if I'm missing something and making a fool out of myself, but based on the fact that pin 2 is physically absent (wtf is going on...), it seems to me that it's indeed impossible to use the dp led for this lcd. Which leaves me confused and stupid. Lesson: next time read the datasheet BEFORE ordering.
7  Community / Products and Services / Re: ArduinoCommander - android application to manage arduino board on: November 17, 2012, 06:22:14 am
I've installed Google Play and installed the app through it. However, still no luck. Are there any log files that I could see to find out what's going wrong on my device?
8  Community / Products and Services / Re: ArduinoCommander - android application to manage arduino board on: October 29, 2012, 01:56:57 pm
wow this seems like a dream app!
I'm trying to use it with a Yarvik 224 tablet smiley-cool, running Android 4.0.3
it's not rooted, but I'm pretty sure that the usb host feature works fine (I can read usb flash drives, connect to mouse/keyboard etc)
I'm uploaded the modified Firmata which I got from your website (StandardFirmata9600.zip) to my Arduino Uno through IDE version 1.0.1, selected 9600 for baud rate from the menu of the application, however my Uno doesn't appear in the Usb devices tab. I'm using the apk I found here https://groups.google.com/forum/?fromgroups=#!topic/tokyohackerspace/Bs4kwrXSJOg, by the way.

Maybe it's an old version? I can't make Google Play work on my tablet, so I can't install the ArduinoCommander app from the official site. Is there a direct link for the last version of the apk? And is there something I could do further to see why my connection fails (eg look as some log files etc).

anyway, it's a great app I hope its development continues
cheers
9  Using Arduino / LEDs and Multiplexing / Re: LED matrix : common anode vs common cathode is there a difference? on: August 06, 2012, 11:08:54 pm

the cheapest ICM7218 I can find on ebay is at 9$ with shipping costs. It's cheaper from distributors as you say but I usually buy almost exclusively from ebay because I don't want to wait to make a big order and save on the shipping costs from a distributor. MAX7219 is as cheap as 1.5$ on ebay. It's just so seducing lol

But anyway, I decided to refrain from buying another led matrix now just to use a MAX, I think I'll use what I have: 595's and 2803; that is the good old way.

Quote from: Riva
Another cheap chip to consider is the WS2801 with a shift register.

yeah I saw this chip recently and it seemed pretty cheap, especially considering it provides I2C. But is it suitable for the application? It has only 3 channels, so to deal with a row or column (8 leds) at a time, I will need 3 of them (?)






10  Using Arduino / LEDs and Multiplexing / Re: LED matrix : common anode vs common cathode is there a difference? on: August 03, 2012, 02:46:50 pm
Maxim has other parts.
http://datasheets.maxim-ic.com/en/ds/MAX6960-MAX6963.pdf
This could be good for another thread that was discussing 2 color & RGB matrices.

thanks, I'll keep those in mind
I see that ICM7218 is much more expensive than MAX7219 in ebay. Actually MAX used to be rather pricey last time I checked, but today I found two pieces for about 3$ from many sellers.
11  Using Arduino / LEDs and Multiplexing / Re: LED matrix : common anode vs common cathode is there a difference? on: August 03, 2012, 02:22:13 pm
nah, I don't think there's something available right now.
I went here http://arduino.cc/playground/Main/MAX72XXHardware and checked each entry, they all mention common-cathode. It was too good to be true lol
12  Using Arduino / LEDs and Multiplexing / Re: LED matrix : common anode vs common cathode is there a difference? on: August 03, 2012, 02:15:40 pm
I did not say that, no.

However, if the MAX7219 multiplexes by driving current into one Digit line and sinking current into 1 Segment line at a time, then electrically you would be okay.
If you ran in no-decode mode and defined your fonts you'd be okay, otherwise things could rotated 90 degrees, or maybe flipped somehow, from what you are expecting.
It would be easy to write a sketch to turn on 1 segment at a time, one register at a time, to see where things ended up.

bingo
that's a good question, HOW does MAX7219 does the multiplexing?
in my simple example, everything seemed to be fine. And what works for one LED works for any other, so the two matrices are identical...nope! That would work if only one LED is lit at a  time, which I'm sure is not the case, without even having to refer to the datasheet, because
-it's hard to imagine the professionals would design it in such an inefficient way
-it's hard to imagine that only I discovered that MAX7219 works with common-anode while everywhere is written specifically "common-cathode"

To be more specific, if we want to switch the two leftmost leds in the upper row, then for the common-cathode it's
ROW1,2,3,4 = L, H, H, H
COL1,2,3,4 = H, H, L, L

if we do the swapping the way I suggested, for the common-anode it will be:
ROW1,2,3,4 = H, H, L, L (the COLS from above)
COL1,2,3,4 = L, H, H, H (the ROWS from above)
and this will result in lighting leds {row, col} = {1,1} and {2,1}
(rows run from top to bottom and cols run from left to right)

even if we rotate by 90 degrees the resulting image will be the mirror of the desired one...yep it's gonna take some software fiddling which I'm not willing to do (I love programming but I'm currently working on other projects), I prefer to buy another led matrix.

I'm just gonna check if there's any library that supports common-anode
13  Using Arduino / LEDs and Multiplexing / Re: LED matrix : common anode vs common cathode is there a difference? on: August 03, 2012, 11:24:52 am
I think if you have 2 MAX7219 trying to drive a 16x8 matrix (2 color) or 3 driving a 24x8 matrix (RGB) there would be a lot of interference between chips as they each try and drive the anodes or the common cathodes for their own 800 Hz multiplexing.

yep you got a point there, because each color matrix will share either the column or the rows with the other...which in turn are driven by separate MAX7219, so this will need a scheme to multiplex the 7219s. I haven't looked in the datasheets if they have such capability, my first though is to switch them on/off alternatively fast enough to get the colors multiplex...but that sounds like a punishment to the chip lol

A better solution would be to use one MAX7219 and connect the anodes (for common-cathode) or cathodes (for common-anode) of each color maxtrix alternatively to it, by using an arrangement of transistor and logic gates that acts as a SPDT switch. That will be interesting to try. (EDIT some 4066 bilateral switches could take care of that, although not in the most efficient way perhaps)

back to the main point though, it seems you agree that a MAX7219 will work with common-anode led matrix just as well?  smiley
14  Using Arduino / LEDs and Multiplexing / Re: LED matrix : common anode vs common cathode is there a difference? on: August 03, 2012, 08:55:22 am
hmmm....but I think that the correct polarity still applies
this is the "interchange" I have in mind:


so for example if on the left of the above picture we have a MAX7219 that is connected to a common-cathode matrix led, its top leftmost led is lit. Now if we connect them to a common-anode matrix of the same physical orientation but swapping the row pins for the column pins, its top leftmost led will also light. The same happens for the other leds, so they are equivalent (I think)

about the colors: since a separate chip will be needed for each color anyway, that means that a multi-color common-anode led matrix can also be used with a couple of MAX7219

I don't know if I'm confused because I hope I'm right and so that I don't have to order another led matrix lol
15  Using Arduino / LEDs and Multiplexing / Re: LED matrix : common anode vs common cathode is there a difference? on: August 03, 2012, 07:58:31 am
I just found a this comment from an older thread http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1234734485:

Quote
For a single color matrix, there is no "common" anything.  A row of anodes and a column of cathodes, one-for-one.  You just have to put the cathode pins LOW and the anode pins HIGH and be able to source and sink enough current through the LED without frying it.

The only meaning the "common" has is when you're talking about multiple colors.  You show an RG matrix with common anodes (each cell has two LEDs wired to the same anode).

so the answer is yes, for single-color matrix only
if the matrix has more than one colors, then the number of the row pins is NOT the same as the number of the columns pins and no interchange can happen...
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