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1  Forum 2005-2010 (read only) / Interfacing / Re: MAX7219 and common anode on: June 08, 2010, 05:10:57 am
The post is ready. With this architecture you can achieve your goal, as long as you can plug up to 8 PCF8574 in the same I2C bus.
2  Forum 2005-2010 (read only) / Interfacing / Re: MAX7219 and common anode on: June 07, 2010, 03:39:44 am
I haven't tested it, but I think you could simply put 7 ICM's and wire all of them to the same Arduino pins. I mean, 1 arduino, 7 ICM7218 and 7 displays. The communication is unidirectional, from the Arduino to the ICM, so I can't see a reason of failure (maybe the Arduino is not able to source enough current, but I don't think the ICM sink too much).
If this don't work, you can put in the middle some PCF8574 and use the I2C bus. I'm preparing another post about this topic.
3  Forum 2005-2010 (read only) / Interfacing / Re: MAX7219 and common anode on: May 21, 2010, 03:34:11 pm
Finally I've found a good solution and it works ok. It's the use of an ICM7218a. With one of these chips I can control 8 digits (2 modules from Sparkfun).
I've written a post including sample code:
4  Forum 2005-2010 (read only) / Interfacing / Re: MAX7219 and common anode on: April 22, 2010, 09:21:59 am
Hi again,
thanks for the info. Just to clarify that with 1 7219 you control 2 modules, so it's cheaper (and I already have them...).
But you've given me the idea to look up at mouser. I think I'll find an equivalent product with commont cathode.
5  Forum 2005-2010 (read only) / Interfacing / Re: MAX7219 and common anode on: April 22, 2010, 07:41:11 am
Well, the problem is that I want 6 modules. So the difference in price is important. And with the MAX I can use the same 3 pins to control all the chips in a daisy chain configuration. With this serial interface I need a pin for every module (right?).
6  Forum 2005-2010 (read only) / Interfacing / MAX7219 and common anode on: April 21, 2010, 12:19:09 pm
I'm planning to buy some of these 4 7-segments I've found:
I want to control them with a MAX7219 (I have some). The problem is that the displays are common anode, while the MAX7219 is supposed to work with common catode devices.
I've thought about two possible solutions and I wish to know if there was any problem with them (my electronic theory is poor...).
1- Use of inverters at the digit pins. If I wire the digit pins to the digit pins of the displays throwgh inverters and I connect the segments pins in the usual way when I send a 0 the led will light and viceversa. So with the arduino I can easily invert the data send to the MAX7219. (Of course, I could use inverters for the segments too).
2- Connecting digits to segments an segments to digits. If I connect the pins of the MAX digits to the display segments and viceversa I'll maintain the right polarity. In that case when the MAX selects a digit, in my display it is actually selecting a concrete segment in every digit. So the transformation that I have to do in the Arduino is more complex, but I suppose it's possible.

I hope you can understand my poor english. So, do you think both solutions are correct? Will I have any problem? Wich one do you considere the best?
Thanks in advance.
7  Forum 2005-2010 (read only) / Development / Re: Library to controll LCD Displays with 2 pins (I2C) on: August 03, 2010, 10:29:59 am
Hi again,
I've been looking the Arduino Playground and I think this library could be published there. I've created an account but I'm not able to edit the corresponding page. Does anybody know how to edit the Playground pages?
8  Forum 2005-2010 (read only) / Development / Library to controll LCD Displays with 2 pins (I2C) on: July 29, 2010, 04:52:19 pm
I've ported the official LiquidCrystal library to control the LCD's via the I2C bus and one or two PCF7584 (generic 8 input/output I2C chip).
I've write this for my next project, in witch I'm already using an I2C bus and I need to add an LCD driver. In that way, I don't need any additional pin from arduino (just analog 4 and 5 I'm already using).
The library is very easy to use because once the object is constructed, the rest of the code is exactly the same as with the original library.
You have an explanation of the library, the source code and some samples here
I think it can be useful for many people.
Feel free to use it. Feedback is welcome.
9  Forum 2005-2010 (read only) / Interfacing / Re: ICM7218A on: May 21, 2010, 03:44:12 pm
with the ICM7218a you don't have to use any resistor. I've tried it with red, yellow, blue and green displays without any problem.
You have a sample here:  
10  Forum 2005-2010 (read only) / Interfacing / Re: Problem with L293D (runs my motor "slow") on: February 10, 2010, 12:54:54 pm
Well, if I were a Lego purist, I wouldn't use Arduino...  smiley
I think I'm going to modify my current lego battery box to fit a lithium battery as you suggested.
I don't want to buy a motor contoller board; a L293D is cheaper!! But I'll investigate this drivers based on MOSFET's to see if I can make something interesting...
11  Forum 2005-2010 (read only) / Interfacing / Re: Problem with L293D (runs my motor "slow") on: February 09, 2010, 05:28:44 am
Thanks for your replys. I'm happy because I didn't do anything bad (I'm a noob in electronics) but sad because I realize I have a problem...
The solution posted by Ran is not good for me because I want to use Lego parts that fit perfectly in my Lego structures... I would have to hack the battery box in order to fit inside some kind of rechargeable battery...

Finally I have another question.
The Lego battery box has a typical small led that lights when you turn the switch on. I've noticed that if I turn the switch off and the hbridge is receiving power from the Arduino, the led in the battery box shines. Do I have to worry about that? Is it dangerous for the batteries or any component?
If I place a diode in the ground wire of the battery box this don't happens, but I have an additional voltage drop...
12  Forum 2005-2010 (read only) / Interfacing / Problem with L293D (runs my motor "slow") on: February 08, 2010, 06:40:06 pm
I have a problem with a HBridge L293D.
I'm using a Lego motor and feeding the motor and the HBridge with diferent power supplyes. To feed the motor I'm using an original Lego battery box (to the  pin 8 on my HBridge) and to feed the HBridge +5 from Arduino (to the pin 16) . I've connected the ground of both power supplies, of course.
With this setup I'm able to control the motor in both directions as well as the speed using PWM. The problem is that I've noticed that when I plug the battery box directly to the motor (without HBridge, arduino...) it turns fastly than when I use th HBridge at maximum speed (sending an analogWrite(255) or even a digitalWrite(HIGH) to the enable pin)
Is this behaviour normal? Am I doing something wrong?
Thanks for your help.
13  Forum 2005-2010 (read only) / Interfacing / Re: RF Modules RX3400 & SAWR (434Mhz) - No Link on: February 05, 2010, 02:19:02 pm
I had exactly the same problem described in the first post by nonfiction, and using VirtualWire it works perfectly. Thanks FusiveResonance.
The explanation why this happens is in the documentation of VirtualWire:

"Why not just use the Arduino UART connected directly to the transmitter/receiver? As discussed in the RFM documentation, ASK receivers require a burst of training pulses to synchronize the transmitter and receiver, and also requires good balance between 0s
and 1s in the message stream in order to maintain the DC balance of the message.

UARTs do not provide these. They work a bit with ASK wireless, but not as well as this
14  Forum 2005-2010 (read only) / Exhibition / Re: Arduino + Lego NXT on: December 03, 2009, 06:29:20 am
great job. I'm new to Arduino and I've got to this from Lego NXT. I think Arduino is much more powerful and flexible than NXT, but I love Lego technich to build, and I already have a good assortment of parts. So I was looking for the way to use Lego elements (motors, sensors...) with Arduino. Your work looks great. I'll try it.
By the way, do you have the schematics of the Power Funcitions motors? Have you connected them to Arduino?
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