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I'd like to use the a Grove RGB LCD on a raspberry Pi. I would like to plug it directly with minimal circuitry.

It's a cheap RGB LCD that use I2C. There's raspberry pi librairies (Python and C)... but it's supposed to be plugged to a Grove Pi wich is more expensive but you don't have to.

Has anyone done that already ?

From my understanding It should work directly, am I right ?

  • Update since I received the LCD. I found some python librairies on GIT : github.com/youngage/grove-lcd. – qkzk Nov 27 '16 at 18:18
  • I connected it directly (using 3.3V pin). The device is showed with sudo i2cdetect -y 1 and the backlight works.... but no way to display any character. I guess i have to use a voltage shifter. I'll keep you informed. – qkzk Nov 27 '16 at 18:27
  • Well ! I finally did it. I used a voltage level converter. RPI 5v directly to grove rgb vcc (it was the key, a collegue advised me to do it, I wouldn't have guessed), sda, scl and gnd through the voltage level converter. It works but it's not stable (yet ?). Many errors but it works... Thanks a lot for your inspiring answers. – qkzk Jan 4 '17 at 18:33
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It should work directly

Probably not directly. Since it is plugged directly into an Arduino on the product page, it presumably uses 5V logic, but this is not a difficult or expensive problem to solve:

How to use Arduino devices with Raspberry Pi?

As for the software libraries, they may or may not work without the Grove Pi, which does appear to have an Atmega chip (the heart of the Arduino) on it. However, this diagram:

enter image description here

Makes it look like I2C communication with Grove device can bypass the Grove Pi (at least in the abstract, since you will probably still need that level shifting). Which strongly implies their software can be used in that context.

If not, since the source is available, it would not be impossible to create a version of it which does work. Presuming that's a fairly standard I2C adapted 1602A compatible LCD, there are I think already a number of libraries in various languages that should work with everything except the RGB aspect.

Beware "not impossible" != "possible for everyone", of course.

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  • I'll read that, thank you. What about the RGB aspect, is there something that can be done except buying a GrovePi ? – qkzk Nov 19 '16 at 18:09
  • Again I'm sure it's not impossible -- just keep in mind my caveat about what that means. I didn't look into their stuff (I presume it's open source because anything else with Arduinos is not viable) but you probably have two different sources you can pick through, the Arduino stuff (C++) and whatever the pi version is in (probably python, but note it may have critical bits in C). I don't even use python, but I found deciphering this kind of thing easy enough w/ Adafruit libraries for their I2C gizmos. Mind you, those gizmos also had datasheets available. – goldilocks Nov 19 '16 at 18:20
  • I think it would be odd if the software did require the Grove Pi because that implies doing pointless and inefficient things with the Atmega chip on it. A sane and more likely approach is it passes transparently through to the device. But I could be wrong. – goldilocks Nov 19 '16 at 18:20
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I2C is pretty standard using SDA and SCL lines (data and clock respectively). You should be able to connect the matching pins from the PI (including power and ground - Do not connect power to the 5 Volt pin of your Pi use the 3.3 Volt pin to avoid damaging your Pi.) to the LCD and use the existing libraries. Grove in this case is the type of connector on your LCD and you can either get a matching grove connector and solder the wires to your Pi or just use some female to male jumper wires. Alternatively, you can get add on boards for the Pi that allow easy connection of grove devices to the Pi's GPIO pins.

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    Worth noting that the "grove connector" is 4 pins all of which correspond directly to something on the Pi, except, as you say, 2 of them expect a different voltage than what the Pi uses. – goldilocks Nov 19 '16 at 16:18
  • Thanks for the info about 3.3v, I wouldn't have guessed... – qkzk Nov 19 '16 at 18:00
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A less expensive and less invasive way to connect Grove Connectors to the Raspberry Pi, is to add a grove shield to the Raspberry Pi, like the Pi2Grover connector.

Then it becomes plug and play with all your Python drivers available.

Here is a tutorial on how to use the devices:

http://www.switchdoc.com/2016/02/tutorial-intro-to-grove-connectors-for-arduinoraspberry-pi-projects/

Faraday

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