Conductor and Digit 1 PCB Assembly¶

Digit 1 and the colons are on a single PCB. Digit 1, powered by a Raspberry Pi Pico 2040, is identical to digits 0, 2, and 3 except it is contained on a single PCB with the conductor. The Raspberry Pi Pico W 2040 (conductor) operates the colons and serves as the central command and control for the display, performing the following functions:

• Sends commands to digits as to what to display (e.g., 0-9, A-F).
• Sends commands for the brightness of the digits.
• When in Admin mode, transmits its own Wi-Fi service to wirelessly change the display settings from a cell phone or computer.
• Manages the scheduler, which is the mechanism for displaying time, date, external temperature and humidity, and interior temperature and humidity.
• When connected to a Wi-Fi network, obtains its public-facing IP address, looks up the time zone it is located in, and sets the display to the local time.
• When connected to a Wi-Fi network, obtains the closest weather station and, depending on the scheduler, may display the external temperature and humidity.
• Manages the low power consumption mode by turning off the power to digits 0-3. When awakened, it turns on the power to digits 0-3.

Front face of the Conductor and Digit 1 PCB fully assembled:

Back side of the Conductor and Digit 1 PCB fully assembled:

Prerequisites¶

• Fabrication of the conductor and digit one PCB.
• 3D print of the upper and lower colons.

Table of components

Quantity	Component	Image
5	16 pin IC socket
5	L293D stepper motor driver
4	20 pin female header connector
1	20 pin single row breakaway male connector
1	Vertical Slide Switch Micro High Knob 3 Pin 2 Position 1P2T SPDT Panel Mount
6	2 Pin PCB Mount Screw Terminal Block Connector Straight Pin
2	0.1μ farad ceramic capacitor
2	1μ farad electrolytic capacitor
1	5mm 0.5 Ω ohm Photoresistor Resistor 5516 GL5516
1	S8550 TO-92 TH PNP Transistor
1	2N2222 TO-92 TH NPN Transistor
2	10K ohm 0805 Resistor 1/4w Metal Film Fixed Resistor
28	5mm Flat top LED, anode long lead (your choice of color)
2	3mm Flat top LED, anode long lead (your choice of color)
1	Raspberry Pi Pico 2040 with Headers
1	Raspberry Pi Pico W 2040 with Headers
1	Conductor and Digit 1 PCB	See next section

Table of tools

Required	Tool	Image
Yes	Soldering station
Yes	0.8mm 1.76oz RoHS flux core solder
Yes	Mini flush cutters
Yes	Isopropyl Alcohol
Yes	Cotton Facial Pads

Assemble Digit One¶

This section will guide you through following the relevant instructions from the Digit 0, 2, & 3 PCB assembly to assemble Digit 1 on the Conductor and Digit 1 PCB.

1. On the front face of the Conductor and Digit 1 PCB, add the 16 pin headers as previously completed for the digit PCBs. Note the highlighted sections in the picture below where you'll add an additional 16 pin header to the Conductor and Digit 1 PCB. Don't forget to snip all the pins flush on the back side of the Conductor and Digit 1 PCB, resolder each snipped pin to a smooth bead, then remove the flux with cotton dabbed with isopropyl alcohol.
   
2. On the front face of the Conductor and Digit 1 PCB, add the 28 5mm LEDs as previously completed for the digit PCBs. Be sure to insert the LED anode (long pin) into the through hole marked with a +. Do not solder the 5mm LED into the Top-LED1 or LWR-LED1 location on the Conductor and Digit 1 PCB. Instructions later in this tutorial will detail how to install the 3mm LEDs into the Top-LED1 and LWR-LED1 locations. Finish soldering the 28 5mm LEDs by snipping all the pins flush on the back side of the Conductor and Digit 1 PCB, resolder each snipped pin into a smooth bead, then remove the flux with cotton dabbed with isopropyl alcohol.
   
3. On the back of the Conductor and Digit 1 PCB, add the motor pins. Note the highlighted sections in the picture below where there are two additional motor pins (pairs) you'll need to add for the colons, and an additional 3-pin connector for the Digital Humidity and Temperature (DHT) sensor. Don't forget to snip all the pins flush on the back side of the Conductor and Digit 1 PCB, resolder each snipped pin to a smooth bead, then remove the flux with cotton dabbed with isopropyl alcohol.
   

Colon Segments LEDs¶

In addition to the soldering equipment you needed when previously mounting the 5mm flat top LEDs, you'll need the two 3D printed colon segments, labeled (A) in the picture below, as fabricated in the 3D print the display parts document.

1. Following label (B) in the picture above, insert the 3mm flat top LEDs into Top-LED1 and LWR-LED1 on the front face of the Conductor and Digit 1 PCB. Follow the same 5mm LED install process and be sure to insert the long lead anode of the LED into the + through hole.
2. Following the picture below, slide the colon segments over the 3mm LED. Note the lower base of the LED lense may need to be lightly sanded with 300 grid sandpaper if it does not easily slide into the colon segment.
3. On the back side of the Conductor and Digit 1 PCB, align the colon segment so its square base is positioned into the square hole of the PCB.
4. Solder the 3mm LEDs into place.
5. Optionally you can use a metric ruler to verify the LEDs protrude perpendicular from the PCB and are 14mm from the PCB to the top of the lens of the LED. This optional step insures the proper length of the 3mm LEDs.

PNP and NPN transistors¶

1. Following the picture below, solder the s8550D PNP transistor into the through hole (mis-) labelled Q3 2N8550 on the front face of the Conductor and Digit 1 PCB. When inserting the transistor's pins into the through holes, be sure to orient the transistors so the flat face matches the silk screen on the PCB as held by the tweezers in the picture.
2. Following the picture below, solder the 2N2222A PNP transistor into the though hole labelled Q2 2N2222 on the front face of the Conductor and Digit 1 PCB.

Headers for the Pico and PicoW¶

On the back side of the PCB, place the four 20 pin headers into the through holes for RASP1 and RASP2. Carefully turn over the PCB while keeping the 20 pin headers in the through holes. Level the PCB and adjust the two 20 pin headers so they are perpendicular to the PCB. To keep the headers perpendicular to the PCB, you can provide a temporary solder onto a pin or use a jig. Solder the pins once in place. Snip all the pins flush, resolder each to a smooth bead, then remove the flux with cotton dabbed with isopropyl alcohol.

Surface mount resistors¶

On the back side of the PCB, solder the two 10kΩ resistors onto the pads marked R2 10k and R3 10k located between the top and bottom rows of the 20-pin headers. Soldering surface mount components require a slightly different skill than through hole soldering as you'll need to use tweezers to center the resistor over the pads and apply a minimal amount of solder.

Install Six, two pin (2P) Terminal Block Connectors¶

There are five 2P terminal block connectors on the front face of the PCB, and one on the back side. The picture below shows a completed install of the terminal block connectors on the front face of the Conductor and Digit 1 PCB. Note the arrows pointing in the direction of the terminal block connector where the wires are inserted into the ports. To follow the steps below, you'll position the front face of the Conductor and Digit 1 PCB up, then work your way from the bottom left corner (1), to the bottom right corner (5).

1. Follow the picture below and insert the 2P terminal block connector into the 5v-D1 through holes with the connector facing LEFT, then solder it into place.
2. Follow the picture below and insert the 2P terminal block connector into the U7, Tx-1 Rx-1 through holes with the connector facing LEFT, then solder it into place.
3. Follow the picture below and insert the 2P terminal block connector into the U7, GPIO19 Tx-0through holes with the connector facing LEFT, then solder it into place.
4. Follow the picture below and insert the 2P terminal block connector into the UART1, Tx-0 Rx-0 through holes with the connector facing RIGHT, then solder it into place.
5. Follow the picture below, insert the 2P terminal block connector into the 5v-D0 through holes with the connector facing LEFT, then solder it into place.
6. Position the back of the PCB up and insert the 2P terminal block connector into the 5v-OUT through holes with the connector facing RIGHT, then solder it into place.

Electrolytic and Ceramic Capacitors¶

1. On the front of the Conductor and Digit 1 PCB, align the electrolytic capacitor - sign opposite the + printed on the PCB for capacitor c01 and c1, see the picture below. Insert the pins into the through holes, then turn the Conductor and Digit 1 PCB over to the back side and solder the capacitors.
2. On the front of the Conductor and Digit 1 PCB, insert the ceramic capacitor pins into the through holes titled c02 and c2. Ceramic capacitors are non-polarized and can be inserted in either direction. Turn the Conductor and Digit 1 PCB over to the back and solder the capacitors.

Mount the Motor Drivers¶

On the front face of the Conductor and Digit 1 PCB, mount the L293D 16-pin IC Stepper Motor Drivers as previously completed for the digit PCBs.

Vertical Slide SPDT Switch¶

On the back of the Conductor and Digit 1 PCB, insert the SPDT vertical slide switch pins into the ON/OFF through holes found on the top right hand corner, then solder into place.

Light Dependent Resistor (LDR)¶

Following the picture below and from the back of the Conductor and Digit 1 PCB, place the two LDR pins into the R1 through holes. Bend the pins of the LDR upward so the head of the LDR fits tightly on the top of Conductor and Digit 1 PCB. Solder the LDR in place once properly positioned.

Congratulations, you've completed assembling the controller and digit 1 PCB!

Conductor and Digit 1 Schematic¶

The schematic in this section (below) represents the Colons & Display Microcontroller portion of the circuit for the Conductor and Digit 1 PCB. This circuit is designed to control the colons of the display, acting as the central hub for communication, power management, and environmental data (interior and outdoor) integration. The Raspberry Pi Pico W 2040 orchestrates all operations, while the supporting components ensure stable and efficient functionality. Below is an explanation of the various components, their purpose, and how the circuitry functions:

Key Components and Their Purpose¶

1. Raspberry Pi Pico W 2040 (Microcontroller):
   Purpose: Acts as the central processing unit for the display. It controls the colons and communicates with the digits.
   Functions:
   • Sends commands to the digits (e.g., what to display, brightness levels).
   • Manages `Wi-Fi connectivity for remote control and time synchronization.
   • Handles scheduling for displaying time, date, and environmental data.
   • Controls power-saving modes by turning off unused digits.
2. 4-Pin UART and Low Power mode pin connector (U7):
   Purpose: Provides communication between the microcontroller and the digits via UART (Universal Asynchronous Receiver-Transmitter).
   Pins:
   • Tx-0, Rx-0, Tx-1, Rx-1: Used for transmitting and receiving data to/from the digits.
   • GPIO19: is used to turn on and off the power to the digits.
3. L293D Motor Driver IC (U5):
   Purpose: Drives the colon motors (top and lower colons) to control their movement.
   Functionality: Allows the microcontroller to control the colon motors for precise positioning.
   Pins:
   • ENABLE1 and ENABLE2: Controls the motor speed.
   • INPUT1, INPUT2, INPUT3, INPUT4: Control the CW and CCW direction of the motors.
   • OUTPUT1, OUTPUT2, OUTPUT3, OUTPUT4: Provide the output signals to the motors.
4. 2-Pin Terminal Block Connectors:
   Purpose: Provide connections for external components like power, UART communication, and sensors.
   Examples:
   • 5V-D1, 5V-D0: Power connections for the digits.
   • UART1, Tx-0, Rx-0: UART communication lines.
   • 5V-OUT: Power output for external components.
5. PNP and NPN Transistors (S8550 and 2N2222):
   Purpose: Act as a switch for powering the DHT22 sensor.
   S8550 (PNP): Used for switching power on or off to the DHT22 sensor
   2N2222 (NPN): Used to drive the base of the S8550 to manage power to the DHT22 sensor.
6. Light Dependent Resistor (LDR):
   Purpose: Measures ambient light levels to adjust the brightness of the display dynamically.
   Placement: Connected to R1 and works with the microcontroller to sense light intensity.
7. Electrolytic and Ceramic Capacitors (C01, C1, C02, C2):
   Purpose: Provide power filtering and decoupling to ensure stable operation of the microcontroller.
   Electrolytic Capacitors:
   
   • Polarized, used for smoothing power supply fluctuations. Ceramic Capacitors:
     
   • Non-polarized, used for high-frequency noise filtering.
8. Vertical Slide SPDT Switch (SW1):
   Purpose: Acts as an on/off switch for the entire circuit where off may be Low Power or Admin mode. When the switch is on and the 12v power supply is plugged in, the display will run using its saved settings which includes the SSID and password to the wifi network. When the switch is turned off, the disconnected 12v power supply is then connected and plugged into wall power, the Pico W provides its own wifi and web service allowing you to direcctly connect to its web page and remotely change the display settings. When the switch is changed to the off position while the display is actively running, then the display will retract all the segments and enter low power mode.
   Placement: Controls its internal wifi service and the flow of power to the display.
9. Resistors (R2, R3):
   Purpose: Limit current and set voltage levels in the circuit.
   R2 and R3 (10kΩ): Pull-up or pull-down resistors for stabilizing signals.
10. LEDs (TOP-LED1, LWR-LED1):
    Purpose: Indicate the status of the colons.
    Placement: Positioned on the PCB to align with the colon segments.
11. DHT22 Sensor Connector:
    Purpose: Provides a connection for the Digital Humidity and Temperature (DHT) sensor.
    Functionality: Allows the microcontroller to read environmental data for display.

How the Circuitry Works¶

1. Power Supply:
   
   • Power is supplied by buck converters through the 5V-OUT and 5V-D1/D0 terminal blocks.
   • Capacitors (C01, C1, C02, C2) stabilize the power supply and filter noise for the microcontrollers.
2. Microcontroller Control:
   • The Raspberry Pi Pico W 2040 serves as the brain of the circuit, controlling all components.
   • It communicates with the digits via UART (U7) and controls the colon motors through the L293D motor driver (U5).
3. Colon Motor Control:
   • The L293D motor driver receives control signals from the microcontroller to drive the colon motors.
   • The ENABLE and INPUT pins determine the speed and direction of the motors.
4. Display Brightness Adjustment:
   • The LDR (R1) measures ambient light levels and sends the data to the microcontroller.
   • The microcontroller adjusts the brightness of the LEDs accordingly.
5. Wi-Fi and Scheduler:
   • The Raspberry Pi Pico W 2040 connects to a Wi-Fi network to synchronize time and fetch weather data.
   • The scheduler manages the display of time, date, and environmental data.
6. Low Power Mode:
   • The microcontroller uses the S8550 and 2N2222 transistors to switch off power to the DHT22 when not in use.
7. User Interaction:
   • The SPDT switch (SW1) allows the user to turn the circuit on or off (low power or Admin mode).
   • The LEDs provide visual feedback for the status of the colons.