A friend requested if it was possible to scroll text across three 8×8 LED matrices, specifically this type from Adafruit, which are very bright.
So, I got to work.
In this post I’ll show how to connect and use a 16 x 2 LCD on a Raspberry Pi.
The LCD I am using is a Blue Character OLED(LCD) 16×2 from adafruit.
This display has ultra-high contrast and any-angle readability. It has the best display I have seen on any LCD.
This LCD uses the HD44780 controller which is present in almost all LCDs.
LCDs that use this controller usually have 14 or 16 pins. This LCD has 16, numbered from 0 to 16 as shown below.
Sometimes these pins are present, but not used. Eg, pins 15 & 16 are for back-light and they are not used on this LCD. It depends on the manufacture.
|HD44780 pins in Detail|
|Pin 2||Supply Voltage for OLED and logic|
|Pin 3||Is usually connected to a potentiometer to control the contrast of the display.|
|Pin 4||The register select signal (RS) determines whether the Data Bit values are interpreted as a command (E.g. clear screen) or data (aka: a character to display).|
|Pin 5||Is the Read/Write pin. In read mode, this pin is used to get feedback from the LCD to work out if the LCD can accept commands or to indicate it is too busy.
We don’t need this function as we can wait the maximum time for a command to be written (200us) before sending the next command.
If read is enabled and Pin4 on the LCD is connected to a pin on your Raspberry Pi, there is a chance that you can destroy your Pi. We only ever want to write to the LCD, we never want to read from it. So this should always be connected to ground.
|Pin 6||The enable pin (E)functions as the command/data latching signal for the LCD. The LCD will latch in whatever is on the Data Bits and process it on the falling edge of the E signal
Meaning, when this pin goes low, the LCD will take the input from the data pins at this time.
|Pins 7 to 14||Are the data pins. In 4 pin mode, only pins 11 to 14 are used.|
|Pins 15 & 16||Are used for the backlight if present.|
Below shows how to wire up the LCD to the Raspberry Pi. We will be using 4 pin mode, so there is no need to connect pins 7 to 10. This LCD doesn’t use the backlight pins, pins 15 and 16. It also doesn’t use the contrast pin, pin 3.
If you want to control the brightness of a LED, the speed of a DC motor or the direction of a servo, you will need PWM.
The video shows PWM being used to control the brightness of some LEDs.
Pulse-width modulation (PWM) is used to control the amount of power supplied to electrical devices, especially to DC motors, servos and LEDs.
PWM is able to achieve this by quickly turning off and on the power to the device. The measurement for this is duty cycle.
Duty cycles describes the proportion of ‘on’; a low duty cycle corresponds to low power, because the power is off for most of the time. A high duty cycle corresponds to high power, because the power is on most of the time.
Duty cycle is expressed in percent, 50% is when the power is on half the time and 100% being fully on.
I was fortunate enough to get access to a prototype of Pi-Pan from www.mindsensors.com during their kickstarter.
The kickstarter has finished and they reached their goal. However they will be selling Pi-Pan from www.mindsensors.com at a future date.
Pi-Pan provides Pan and tilt movements for your Raspberry Pi Camera.
Pi-Pan can pan 180 degrees (from left to right) and tilt 110 degrees (top to bottom).
Pi-Pan comes with two servos, a controller board, screws, a mount and instructions. It also comes with some python code that shows how the device can be operated.
(The controller board in the image below is a prototype and the production board will be a lot smaller.)
In this post I show how to control the GPIO on a Raspberry Pi using a touchscreen.
This is a follow up on my previous post Programming for a Touchscreen on the Raspberry Pi
The TFT doesn’t come up too well in the above video. The picture below gives a better idea of how it looks. Click to enlarge
Link to the code;
In the above code touchbuttons.c creates three buttons on the TFT which will be used to turn on/off three LEDs.
To accept input from a touchscreen we have to use the event interface of the Linux input system. We use the ioctl capabilities of the event interface, in addition to the normal read and write calls to get information from the touchscreen. This blog post explains how to use the touchscreen within your own programs using C as well as writing directly to the framebuffer.
Link to the code;
I have spend the last month creating a new version of PiBBOT (Pi Balancing roBOT) , PiBBOT V2.
This version has a sturdier frame and a LCD display. I replaced the 1.8″ TFT with a LCD as the TFT was causing delays in the main loop timing. I also added a very slim battery for the Raspberry Pi.
The code for this project can be found here;
Take a look at two of my previous blog entries for more detail;
Success with a Balancing Robot using a Raspberry Pi
Guide to interfacing a Gyro and Accelerometer with a Raspberry Pi