Time Square — A Raspberry Pi Clock
I had three LCD screens (16x2), one 3.5” RPI display, and two Raspberry Pis lying around and gathering dust. It had been three years since I had worked on an Arduino/Raspberry Pi project. It was time to see how much I still remembered about making circuits work.
As usual, I decided to challenge myself. I put forth two challenges,
- Use Art and Craft materials to make something different
- Use Vim to write/edit the code
I was able to use some of my creative juice to beautify my usual digital clock, but I gave up on my second challenge.
A few years back, I read a tweet,
I couldn’t exit Vim, so I learned it.
Well, I did learn to split the screen vertically and horizontally, copy from one file to another, and use commands such as p, P, d, dd, set nu or set compatible, etc., but it was high time I learned to exit Vim and speed up the development process.
The idea was to develop a digital clock to show the date, time, and temperature.
But it had to be different. I decided to align the LCD screen vertically to show the dates.
Check the image below to get the idea.
The concepts I learned were -
- Not all 16x2 LCD screens are the same
- Creating custom characters
kivyfor desktop app creation- Connecting the RPI screen not using the GPIO provided at the back but using a minimum number of jumper wires
- Connecting multiple LCDs to Raspberry Pi
- and finally, a few things about Raspberry Pi
Let’s take one at a time.
RASPBERRY PI
RTFM has been the mantra for becoming a good programmer, but in the days of 30-second YouTube shorts, it has been reduced to TL; DR. However, sometimes, it is good to refer to documentation.
For example, I used to Google for the pin header diagram, but Raspberry Pi has an out-of-the-box command.
pinout
J8:
3V3 (1) (2) 5V
GPIO2 (3) (4) 5V
GPIO3 (5) (6) GND
GPIO4 (7) (8) GPIO14
GND (9) (10) GPIO15
GPIO17 (11) (12) GPIO18
GPIO27 (13) (14) GND
GPIO22 (15) (16) GPIO23
3V3 (17) (18) GPIO24
GPIO10 (19) (20) GND
GPIO9 (21) (22) GPIO25
GPIO11 (23) (24) GPIO8
GND (25) (26) GPIO7
GPIO0 (27) (28) GPIO1
GPIO5 (29) (30) GND
GPIO6 (31) (32) GPIO12
GPIO13 (33) (34) GND
GPIO19 (35) (36) GPIO16
GPIO26 (37) (38) GPIO20
GND (39) (40) GPIO21
J2:
GLOBAL ENABLE (1)
GND (2)
RUN (3)
J14:
TR01 TAP (1) (2) TR00 TAP
TR03 TAP (3) (4) TR02 TAP
Secondly, the RPI is loaded with three LCDs and one RPI screen. The board would become hot, and to avoid overheating, I had to put in heat sinks and a fan (5v). This meant I needed a way to check the current voltage, amperage, and temperature.
Here comes vcgencmd.
tushar@raspberrypi:~ $ vcgencmd measure_temp
temp=50.6'C
tushar@raspberrypi:~ $ vcgencmd measure_volts core
volt=0.8563V
tushar@raspberrypi:~ $ vcgencmd get_throttled
throttled=0x0
There was no way to check the exact amperage without buying additional hardware, so I had to chuck it. I could have used a multimeter, but I didn’t see RPI complaining about overheating, so I abandoned it.
LCD Screens
Not all LCD screens are the same
Initially, I was using Adafruit’s CircuitPython_CharLCD. This works if we connect the LCD’s individual pin to RPI, but it fails when I use an LCD with an i2c interface. I was on the verge of giving up when I came across RPLCD. The document mentioned that -
Supported I²C Port Expanders
PCF8574 (used by a lot of I²C LCD adapters on Ali Express)
MCP23008 (used in Adafruit I²C LCD backpack)
MCP23017
That’s it. My LCDs were PCF8574. I found this by using a magnifying glass to check the i2c adapter.
Check the image below.
Custom Character
The LCD has 16 columns and 2 rows. The library has a wrapper to write each character(predefined and baked into the library) in one of the cells. I used custom characters for all 16 columns and 2 rows to display one character. For that, I had to know that each cell has 5 tiny lights in a row and 8 such rows. Each row could be on or off using 0 or 1. Using b00111 will light up the three
lights on the right, and two will be turned off. There is an excellent website to generate such binary codes for 1 cell.
Connecting Multiple LCD
Since the LCDs use i2c, it should be enabled (by default, it is disabled on Raspberry Pi) by navigating to raspi-config and then to display and turning on the i2c option.
By default, the LCD port was x27; one can check by using the command -
tushar@raspberrypi:~ $ i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- 23 -- -- 26 27 -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
tushar@raspberrypi:~ $
I have 3 LCDs connected, it shows ports
x23,26 & 27.
i2c uses SDA and SCL to transmit data, and there is only 1 such pin in the Raspberry Pi (GPIO 2 & GPIO 3). To individually manage each LCD, it should listen to three different ports. This can be done by soldering A0, A1 & A2 pins. Check out the image.
This refers to a 3-bit offset; if two boxes in column A2 are soldered, it represents binary 100 (the index number represents the position; the two in A2 mean the second position from the right, starting with zero). Since 100 is 4 in decimal, the new port is 27-4=23.
3.5” RPI Screen
The RPI screen is a plug-and-play screen; the display will latch comfortably onto the RPI GPIO pins. Since I had other wires from LCDs, I had to use jumper wires to connect them. Now I can take 26 wires and connect each pin, but then what’s the fun in that. Refer to the excellent wiki -
The section on the interface refers to the mapping and function of each pin. I used only one power connection, one ground, and multiple pins except those categorized as NC or Not Connected. I didn’t need the touch ability, so I removed the touch-related pins, but the display didn’t work, so I added them back.
kivy
I find tkinter not so fancy. qt is fancy but too complicated. Here comes kivy!! I am surprised that I didn’t know about kivy, an excellent library for creating desktop apps.
The project has been a roller coaster ride for almost a month, but it felt worth it when I completed it today.
Now, I’m moving on to another project: converting my LED strips to a grow light specification. Until then, have fun!!
Code can be found at - https://github.com/tusharacc/time-square