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1  Using Arduino / Displays / Re: I’m Building a 1602 LCD Shield with the PCF8574 - Which Library to Use? on: April 25, 2013, 08:35:23 pm
Thanks again. My shield is done and is working great. Now that I started working more closely with the fm library I see how awesome and flexible it is. If only I had looked closer at it before.

All those hours I wasted searching for a good library to work with my China-made mkjdz board. Why do they scrape off the IC chip part numbers? It makes things so difficult.
2  Using Arduino / Displays / Re: I’m Building a 1602 LCD Shield with the PCF8574 - Which Library to Use? on: April 18, 2013, 05:51:07 pm
Thanks for the advice. I'll look into some of the finer points of that library. I didn't realize that fm's library was not tied to a specific hardware configuration. It certainly seems like the best option.
3  Using Arduino / Displays / I’m Building a 1602 LCD Shield with the PCF8574 - Which Library to Use? on: April 17, 2013, 08:34:25 pm
I'm building a simple 1602 Shield for the Arduino Uno with the PCF8574 (or PCF8574A). I’m trying to decide which library/configuration I should use? There seems to be two different standards for connecting the PCF8574 to the 1602. One uses the lower nibble on the PCF8574 (P0-P3) to control the 1602 D5-D7 pins (with the upper nibble managing the control wires). This standard is associated with the original Arduino I2C LCD library. This library has been supplanted by the "New" library by fmalpartida.

The other standard uses the upper nibble of the PCF8574 (P4-P7) to control the 1602 D5-D7 pins. This standard has been established by DFRobot and their 1602 I2C controller card. This standard is also the standard employed by many other low-cost boards currently being manufactured in China. All these use the DFRobot I2C library.

This difference is well explained in the post at

The difference between these two wiring standards and associated libraries seems to have created quite a bit of confusion for folks trying to get their 1602 working with their Arduino I2C pins.

I'd like to design an I2C 1602 LCD shield but I don't want to create a new standard and I would like my shield to be able to use one of the two libraries already out there. I would like to make things as simple as possible and reduce the confusion that has been caused by these two different wiring standards.

The fmalpartida library is very good, but the DFRobot configuration seems to be quickly becoming the standard due to the flood of clone boards coming out of China.

I am seeking recommendations on which wiring/library standard I should use. I can't seem to determine which library is more widely used or preferred.
4  Products / Arduino Due / Re: Driving LEDs directly from the output pins without using a resistor on: December 20, 2012, 09:13:12 pm
Thanks for clarifying things for me. It make much more sense now. These are all great solutions. I'm still committed to driving my LED cube with the Due, so I'll pick one that works best for me. I'll look into those LED driver chips. They sound perfect.
5  Products / Arduino Due / Re: Driving LEDs directly from the output pins without using a resistor on: December 19, 2012, 09:24:22 pm
GM, can you or anyone else here offer me a bit more assistance. I'm still confused with the theory and application of using these LEDs with the Due.

What would be the best practices when attaching these high-brightness LEDs:
    3.4V forward drop (3.0 ~ 3.6v)
    Max continuous current 20mA
    Resister needed (at 5V): 82 ohm

Should I really be adding tiny valued series resistors? It would certainly be within the fudge-factor to add a small, 10 ohm resistor. I have a background in electrical theory, but I simply don't see the point of adding resistors with such small values.

Or, perhaps, is the answer to simply not use these LEDs with the Due? (As I mentioned earlier they seem to work fine.) Should I simply stop using the LEDs with FV near the output voltage of digital pins? I have plenty of LEDs with FV of 2.2. Should I use those instead?
6  Products / Arduino Due / Driving LEDs directly from the output pins without using a resistor on: December 19, 2012, 02:10:45 am
I've been building projects with the Arduino Due for a while now. I've been building many different multi-LED projects using the digital output pins 24 - 51. The LEDs that I've been using are the 5mm bright white LEDs with a Forward Voltage of about 3.4V.

I was concerned at first, but I've been successfully driving the LEDs without using any current-limiting resistor. I've been building a lot of flashing devices, so I'm generally not trying to light more than one or two LEDs at a time. I've found that many LEDs have a FV of about 3.2 - 3.4 volts. Is there any reason why I shouldn't drive these LEDs directly from the digital outputs without using a current-limiting resistor if they have a 3.2 or 3.4 FV?

I'm planning on building some 5x5x5 or 6x6x6 LED cubes and driving them with the Due. Construction will be greatly simplified using the Due since I will not need any multiplexing circuitry for these sized cubes. Would there be any problems to build these LED cubes without using any current-limiting resistors?
7  Products / Arduino Due / Re: Arduino due pin voltage on: December 07, 2012, 04:21:06 pm
I think it does make a big difference. You should think about what you want to do. I purchased my first Arduino because I wanted to work with the LoL LED shield. I purchased a Leonardo and when it was all put together it did not work because the LoL is not compatible with the Leonardo. I then had to purchase an Uno to get my LoL working.

Now that I have the Due I've been working with devices that I know will work well with it. Most of my latest projects involve using many individual LEDs. The plethora of digital outputs on the Due make complex LED circuits much easier to build and control because you don't need all those shift registers.

My advice is to decide what type of work you want to do. If you want to use a lot of currently available shields and libraries, then get the Uno. If you plan on building all your own circuits and libraries then get the Due.
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