RGB LCD's, Raspberry Pi, and i2c control
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RGB LCD's, Raspberry Pi, and i2c control

by Byrd on Thu Jan 03, 2013 7:00 pm

First Post!

I mainly needed some asurance that I was reading everything correctly before I pulled the trigger on the product that best controls the Red's/Greens/Blues through the i2c bus. There are currently three different options that we (as 18pin RGB LCD & Raspberry Pi owners) potentially have (with a little work):

1. http://adafruit.com/products/715 / Adafruit I2C Controlled + Keypad Shield Kit for 16x2 LCD
The Quote: "The shield is designed for 'classic' Arduinos such as the Uno, Duemilanove, Diecimilla, etc. It will also work perfectly with Arduino Mega R3's." is making me think it'll only work with Arduinos and not a RPi even though it's configured for a 18pin LCD, has the chipset/resistors, and uses i2c. Instead of using the LiquidCrystal library of an Arduino we could just use Python. I did notice that there's more resistors, potentiometers, etc. so it might not work.

** When I went to the Adafruit RGB LCD for Raspberry Pi tutorial the first "Featured in this Article" product is for the same shield but with an LCD in the Arduino section. This product is "In-Stock" **

Tutorial: http://learn.adafruit.com/adafruit-16x2 ... i/overview
Featured in this article link: http://adafruit.com/products/714

2. http://adafruit.com/products/714/ RGB LCD Shield Kit w/ 16x2 Character Display - Only 2 pins used!
This is the same product in the "Featured in this article" link. Problem is, at the very bottom the tutorial link goes to the RGB LCD Shield tut found here (http://learn.adafruit.com/rgb-lcd-shield) which looks to be for an Arduino. This product is also in the Arduino Shield section.

** This package is NOT in stock however the shield (#1) IS in stock -- Seems like the 16x2 RGB LCD is out of stock BUT the 20x4 RGB LCD's are in stock (https://www.adafruit.com/products/499) and could be used just the same.

3. https://www.adafruit.com/products/1109 / Adafruit RGB Positive 16x2 LCD+Keypad Kit for Raspberry Pi
This is the only one listed for the Raspberry Pi for RGB. This product is out of stock even though the shield (#1) is in stock and we can use the 20x4 LCD.

The backpack listed in the LCD section (https://www.adafruit.com/products/292) for i2c does NOT allow for the RGB pins. It's only for 16pin boards and not 18pin. From the link "You can try to connect our RGB 16x2 or 20x4 LCDs up but this backpack will not control the RGB backlight so you'll have to use the backpack only for the 14 digital IO pins (pins #1-14) and connect the backlight pins (#15-#18) directly to your microcontroller with 4 extra wires for color/PWM control as if they were just an RGB LED." -- Raspberry Pi's only have one PWM GPIO (#18 i think) and thus could not control the RGB like an Arduino could in this situation = Can't use an RPi :( :(

Can I just purchase the shield (#1) and use it for the Pi even though it's listed for the Arduino? All the listings and guides run me in circles and I've spent wayyy too much time trying to sort it out. Any help is much appreciated! Getting frustrated :evil:
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Re: RGB LCD's, Raspberry Pi, and i2c control

by adafruit_support_bill on Thu Jan 03, 2013 7:52 pm

A lot of options on the table there. I'll try to summarize as best I can.

The best option for the Paspberry Pi is #3 because it is designed to plug directly into the GPIO header of the Pi, and work with 3.3v logic.

The Shields designed for the Arduino can be made to work with the Pi because they communicate via I2C. However, they are designed for the 5v Arduino, so you would need a level shifter to use it with the 3.3v Pi. http://www.adafruit.com/products/757

You can use the 20x4 displays on either the shield or the Pi-Plate - but be aware that it will obscure the buttons and the contrast control.
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Re: RGB LCD's, Raspberry Pi, and i2c control

by Byrd on Thu Jan 03, 2013 8:45 pm

Thank you for the quick reply!

There seems to be a few ways to skin a cat. I liked Option #3 also however it's out of stock and by your post the shield by itself is not an option as the shield for option #1 is different. The website and tutorials are a little misleading :wink: .

Would the shield by itself be an option for the Raspberry Pi? Maybe it's only listed out of stock bc of the 16x2 LCD just like the Arduino shield? I already have a RGB LCD (I have this one: http://www.adafruit.com/products/499).

Thanks again for your help
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Re: RGB LCD's, Raspberry Pi, and i2c control

by adafruit_support_bill on Thu Jan 03, 2013 9:04 pm

by your post the shield by itself is not an option as the shield for option #1 is different.

I think you are confusing Pi-Plates with Shields. Shields are designed for Arduinos. Pi-Plates are designed for the Raspberry Pi. Before the release of the Pi-Plate, several of our more experienced customers successfully interfaced the Shields to the Pi - with special care to match the logic levels.

The website and tutorials are a little misleading

If you can tell us what specifically you feel to be misleading we will look into it.

Do to the high demand, we currently do not have any of the Pi-Plates in stock (with or without displays). You can sign up to be notified when they are back in stock here: http://adafruit.com/products/1109
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Re: RGB LCD's, Raspberry Pi, and i2c control

by Byrd on Thu Jan 03, 2013 10:54 pm

If you can tell us what specifically you feel to be misleading we will look into it.


I don't mean to sound negative, but please reread the first post. The tutorials for interfacing the RGB LCD's with Raspberry Pi's feature shields and LCD's specifically for Arduinos and make no mention of a necessary level shifter in any situation. This leads the consumer to believe that the Arduino kit could in-fact be used with the Raspberry Pi's without any further purchases. The level shifter was not mentioned in the suggestions sections at the bottom either.

At the very least, I'd suggest to feature only the Pi-Plate/LCD in the tutorial OR specifically mention that in order to use an Arduino shield you'll need a level shifter with instructions on how to install it. Differentiating between a Pi-Plate and Arduino Shield may need to be more pronounced given the intermingling of tutorials/packages and similarity.

From a business standpoint: For packages of shield's and LCD's or Pi-Plates w/ extras etc. - let the customer choose which size LCD they'd want with the shield and if the 16x2 LCD is not in stock, they could decide whether to spend an extra $10 more to go with the 20x4" LCD or wait the 5-10 business days for that size. I know it's more back end programming and pain to go change it now but long story short you're losing out on revenue and giving the customer an opportunity to go elsewhere.

I've only purchased products from you guys and will continue to do so. It's just free insight from a new guy which could save time and effort answering questions on your end, frustrated customers, and potentially lost revenue in the long run.

Do to the high demand, we currently do not have any of the Pi-Plates in stock (with or without displays). You can sign up to be notified when they are back in stock here: http://adafruit.com/products/1109


Currently on the list! :D Thanks again.
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Re: RGB LCD's, Raspberry Pi, and i2c control

by adafruit_support_bill on Fri Jan 04, 2013 6:13 am

please reread the first post. The tutorials for interfacing the RGB LCD's with Raspberry Pi's feature shields and LCD's specifically for Arduinos and make no mention of a necessary level shifter in any situation.

You are still confusing Pi-Plates with Shields. The tutorial that you linked is for a Pi-Plate, specifically designed for the Pi at 3.3v. If you look at the tag-line it says:
Code: Select all | TOGGLE FULL SIZE
This new Adafruit Pi Plate makes it easy to use an 16x2 Character LCD with a Keypad

I'll see if we can do a better job of highlighting the differences. They do look visually quite similar.

We do offer the Shield both with and without the display. The Pi-Plate is still very new and they are going out the door faster than we can make them. We may offer them without displays in the future.
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Re: RGB LCD's, Raspberry Pi, and i2c control

by jonwatts on Mon Apr 01, 2013 9:33 pm

Hi,

I'm feeling lost in this as well. Is the LCD Backpack http://www.adafruit.com/products/292 a shield, a plate, or universal? I bought one for my Raspberry Pi to use with an RGB LCD http://www.adafruit.com/products/398 (not realizing the pi plate with buttons would probably be less of a headache).

I started with the a servo controller http://www.adafruit.com/products/815 and haven't been able to have it show up using i2cdetect, so I tried with this LCD backpack and still no joy. I'm using the Adafruit 5v 2amp power pack for the LCD and servo power but don't seem to be getting anywhere. Can someone point me in a direction to look or can I attach some pictures or maybe send the whole thing to Adafruit for a sanity check?

Thanks,

Jon
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Re: RGB LCD's, Raspberry Pi, and i2c control

by tldr on Tue Apr 02, 2013 9:36 am

i would not use that backpack with a pi. it needs 5v to run the lcd and has pullups on the i2c lines, so you'll be exposing the i2c pins on your pi to 5v.

the servo shield ought to be ok, though, since it will run at 3.3v.
"If I had known it was harmless, I would have killed it myself." - Phillip K. Dick, A Scanner Darkly
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Re: RGB LCD's, Raspberry Pi, and i2c control

by jonwatts on Tue Apr 02, 2013 2:07 pm

Thanks for that, tldr.

To Adafruit, I have been thoroughly impressed with your product offerings, Occidentalis and the Raspberry Pi webide; but I can echo what byrd said previously about the product descriptions and tutorials not being clear in some critical areas. I'd also been over the product page and tutorial a number of times before buying this backpack. Shouldn't there be a note somewhere stating that connecting a 5V device to a 3.3V controller may damage the controller? I would think the importance of your logic level converter http://www.adafruit.com/products/757 would be made obvious on the Pi's product page and tutorials, as well as those of the accessories. I feel like I'm learning this the hard way by throwing more time and money at the problem.

I was just trying to troubleshoot the problem I'm having connecting my Pi to the Adafruit servo controller over i2c. Now I find out I may have damaged my Pi in the process? This isn't making my job any easier.

I'd suggest adding a list of "Works with" controllers in the "Technical Details" section of the product page and at the top of all tutorials for products that span a range of controllers.

Jon
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