Wetbulb Rack Wiring

Do one step at a time and tick it off when it's done. Your progress is saved.

+ rail (red) − rail (blue) Arduino pin nothing

⚠️

Unplug everything before you start. No USB cables plugged in while you wire.

🎉 All done! Your rack is wired and tested.

Power (HW-131)

The HW-131 powers the breadboard from a USB port. The Arduino gets power from the laptop.

Which rail is "top" and which is "bottom"?

1Lay the breadboard flat in front of you, long side going left to right.
2The 2 rails along the far edge (away from you) are the TOP rails.
3The 2 rails along the edge closest to you are the BOTTOM rails.
4Each edge has one + red line and one − blue line. Use the lines printed on your board.
5The HW-131 sits on one end and plugs into all 4 rails at once.

Easy trick: stick a bit of tape on the far edge that says LOGIC and on the near edge that says MOTOR. Don't turn the board around after that.

Look for a gap: on some long breadboards the red/blue lines have a break halfway along. That means the rail is cut in two. If yours has a break, add a short jumper wire across the gap on each of the 4 rails.

Push the HW-131 onto one end of the breadboard. Its pins go into both the top and bottom rails.
Check: HW-131 + is in the + red rail, and − is in the − blue rail. Some boards line up backwards!
Set both HW-131 jumpers to 5V (not 3.3V, not OFF).
Plug a USB cable into the HW-131's USB port. Don't plug the other end in yet.
Arduino GND→top − rail
top − rail→bottom − rail (one jumper wire, so all grounds are joined)
Arduino 5V→nothing Leave it empty.

Remember: Top rails are for the screen, sensor and joystick. Bottom rails are only for the fan motor. This stops the motor messing up the screen.

Temp Sensor (DHT11)

Plug it straight into the breadboard, then run 3 short wires.

How it looks (close-up of the top half)

Push the DHT11 straight into the top half of the middle (row e, next to the middle gap). Each pin goes in a different column. Grid facing you.
Read the labels on the sensor. Remember which column has +, S and −. (Yours may be in a different order than the picture.)
+ column→top + rail (short wire)
− column→top − rail (short wire)
S column→D7

Why this works: the 5 holes in each column (a–e) are joined inside the board. Put a wire in any free hole in the same column as a pin and it's connected to that pin. Never put two sensor pins in the same column.

Bare blue sensor with 4 legs (no little board)? Push all 4 legs into 4 columns. Left to right (grid facing you): VCC, DATA, unused, GND. Then push a 10 kΩ resistor across, with one leg in the VCC column and one leg in the DATA column. Nothing goes in the "unused" column.

Screen (LCD with 4-pin I2C board)

Your screen has a small board on the back with 4 pins. Only 4 wires!

LCD GND→top − rail
LCD VCC→top + rail
LCD SDA→A4
LCD SCL→A5

Easiest way: use female-to-male jumper wires. The female end slides onto the LCD pin, and the male end goes into the rail or Arduino.

Can't see A4 / A5? They're on the Arduino's analog row, next to A0–A3. (The SDA and SCL pins next to AREF, at the end of the digital row, are the same pins, so either spot works.)

The code must use the I2C screen. The old code was written for the 16-pin screen. It needs the LiquidCrystal I2C library (see Step 7). Contrast is now set with the small blue knob on the back of the LCD, not the joystick.

Fan Motor + ULN2003

Use the bottom rails only. Ground is already done — just connect the ULN2003 and fan.

✓

Ground is already connected! Your bottom − rail already has ground from Step 1 (and Board − is on it). You only need to plug in these remaining wires for the ULN2003 and fan:

How to connect the ULN2003 (bottom rails)

Board has 4 little LEDs and a white 5-hole socket. Only 4 connections needed:

Board IN1→Arduino D9 (control signal)
Board +→bottom + rail (power for board)
Motor wire 1→bottom + rail (fan power)
Motor wire 2→one hole of the white socket (see tip below)

Finding the right socket hole: after you upload the code, press the Arduino's RESET button. The motor will spin for ~1 second and LED A lights up. If it doesn't spin, move wire 2 into the next hole and press RESET again.

16 legs. Notch at the top. Pin 1 is top-left.

Chip pin 1 (IN1)→Arduino D9
Chip pin 9 (COM / +)→bottom + rail
Motor wire 1→bottom + rail
Motor wire 2→Chip pin 16 (OUT1)

ULN2003 gets hot or the motor is weak? Also connect IN2 to D9, and OUT2 (chip pin 15, or the next socket hole) to motor wire 2. Now two channels share the load.
The HW-095 isn't used.

Joystick (5 pins)

5 wires.

Turn On (order matters!)

The HW-131 always goes first.

First: plug the HW-131's USB cable into a USB port (laptop or phone charger).
Press the HW-131's power button. Its LED lights up.
Then: plug the Arduino into the laptop. (If it was already on, press RESET.)

Why? If the Arduino starts first, the screen has no power yet and shows garbage. Fix: press RESET.

Upload the Code

In the Arduino IDE.

Install DHT Library: In Arduino IDE go to Tools → Manage Libraries, search for DHT sensor library by Adafruit, click Install, then click Install All.
Install I2C LCD Library: Still in Manage Libraries, search for LiquidCrystal I2C by Frank de Brabander and click Install.
Open Sketch: Go to File → Open and select wetbulb_rack/wetbulb_rack.ino (or copy the updated code into the editor).
Select Board: Go to Tools → Board → Arduino AVR Boards → Arduino Uno.
Select Port: Go to Tools → Port and choose the one that says Arduino Uno (e.g. COM3, COM4, etc.).
Upload: Click the Upload button (→) at the top left. Wait until it says "Done uploading" at the bottom.

Testing & Results Checklist

Run these 7 quick tests. Each step tells you what to do and what you should see happen.

Test 1: Boot & Fan Self-Test
Turn on the HW-131 first, then plug in the Arduino (or hit the Arduino RESET button). 👀 Expected Result: The screen lights up showing ~WETBULB with a loading progress bar. At the exact same time, the fan spins for ~1 second and LED A on the ULN2003 lights up.
(If the fan didn't spin, move Motor wire 2 into the next white socket hole and press RESET again).
Test 2: Display & Text Sharpness
Wait 2 seconds after boot finishes for the main status screen to appear. 👀 Expected Result: The screen shows *COOLING and H2O 0.XL (or ~FREEAIR if ambient air is cool/dry).
(If screen is blank, dark blue boxes, or dim: gently turn the small blue trimmer knob on the back of the LCD with a small screwdriver until text is razor sharp).
Test 3: Joystick Left / Right (Screen Switching)
Nudge the joystick to the left or right. 👀 Expected Result: The screen title briefly flashes (e.g. <STATUS>, < AIR >, <WETBLB>, <WATER >, < CO2 >, <FOCUS >), then reveals live telemetry and bar graphs for that metric.
Test 4: Joystick Up / Down (Priority Tuning)
Navigate to the <FOCUS > screen, then push the joystick UP or DOWN. 👀 Expected Result: The knob icon slides horizontally along the slider between CO2 and H2O, adjusting the data center's carbon vs. water optimization balance.
Test 5: Live Climate Sensor & Fan Response (Breath Test)
Cup your hands around the blue DHT11 sensor and breathe warm humid air onto it for 5–10 seconds. 👀 Expected Result: Within 10 seconds, humidity and wet-bulb numbers climb. The fan automatically kicks in (or speeds up) in proportion to the rising cooling-water demand!
Test 6: Serial Telemetry
In Arduino IDE click Tools → Serial Monitor. Set the bottom baud dropdown to 115200 and line ending to Newline. 👀 Expected Result: The Arduino outputs a live data string every 2 seconds like S,23.4,61 (Temperature °C and Humidity %). When you flick the joystick, it prints J,PAGE,x or J,W,x.
Test 7: Remote Command Simulation & Ready for App
In the Serial Monitor's top input box, paste: L,*RUN NOW,~-24%H2O,200,380,50 and hit Enter. Next paste: L,WAIT 3h,~-24%H2O,0,410,50. 👀 Expected Result: On the first command, the screen displays RUN NOW with a spinning fan icon and the fan runs at PWM 200. On the second command, the screen displays WAIT 3h and the fan stops.
⚠️ IMPORTANT: Close the Serial Monitor window now so your Python dashboard can connect to the port!

Something Wrong?

Tap a problem to see the fix.

Screen is blank or shows solid boxes

Press RESET on the Arduino.
Turn the small blue knob on the back of the LCD slowly all the way one way, then the other. The text usually appears somewhere in the middle.
Check SDA is on A4 and SCL is on A5 (not swapped).
Still nothing? Your screen's address may be 0x3F instead of 0x27. Change it in the code and upload again.

Screen goes crazy when the motor starts

Make sure the motor is only on the bottom rails.
If you have a small 0.1 µF capacitor, put it across the motor's 2 wires.

Backlight is off

There's a small jumper on the end of the LCD's back board. Make sure it's pushed on.
Check GND and VCC go to the top rails and the HW-131 is on.

Screen says SENSOR? or CHECK D7

The sensor DATA wire isn't on D7. Move it.
Bare 4-pin sensor? It needs the 10 kΩ resistor.

Motor hums or twitches but won't spin

At the top of the code, change MIN_RUN_PWM from 90 to 140.
Upload again.

Motor never spins

Is the HW-131 on? (LED lit)
Are both jumpers on 5V?
Is the top − rail joined to the bottom − rail, and is Arduino GND on the − rail?
Driver board: try motor wire 2 in a different socket hole.

Nothing works and the HW-131 LED is off

Press the HW-131's power button.
The USB port may be too weak. Try a different USB port or a phone charger.

Joystick directions are backwards

At the top of the code, set FLIP_X, FLIP_Y or SWAP_XY to true.
Upload again.