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Board/platform: Arduino Uno R3 (ATmega328P, genuine) Module/component: 16x2 LCD with PCF8574 I2C backpack (I2C address 0x27) Power supply: Arduino powered via USB from PC (5V) LCD module powered from Arduino 5V pin Common ground: yes, LCD GND connected to Arduino GND Wiring: LCD SDA → Arduino A4 LCD SCL → Arduino A5 LCD VCC → Arduino 5V LCD GND → Arduino GND No external pull-up resistors added (relying on onboard ones from backpack) Code snippet: cpp #include <Wire.h> #include <LiquidCrystal_I2C.h> LiquidCrystal_I2C lcd(0x27, 16, 2); void setup() { lcd.init(); lcd.backlight(); lcd.setCursor(0, 0); lcd.print("Hello World"); } void loop() { }Libraries/IDE: LiquidCrystal_I2C v1.1.2 (Frank de Brabander fork), Arduino IDE 2.3.2 Error/log output: No compile errors. Sketch uploads successfully. Backlight turns on, but no characters appear on screen.Expected vs actual: Expected "Hello World" to appear on the first line. Instead, backlight lights up but display remains blank — no visible characters, not even garbled ones. Tests already performed: Ran I2C scanner sketch — confirmed device found at address 0x27 Adjusted the contrast potentiometer on the back of the I2C backpack fully in both directions — no visible change Tried address 0x3F as a fallback — I2C scanner still reports 0x27, so ruled that out Measured 5V present at LCD VCC pin with multimeter Swapped SDA/SCL to confirm not reversed — no change

Board/platform: Raspberry Pi 4 Model B, 4GB RAM, Raspberry Pi OS (64-bit, Bookworm) Module/component: 4-channel relay module (5V, opto-isolated, JQC-3FF-S-Z) Power supply: Raspberry Pi powered via official 27W USB-C adapter (5V/5A) Relay module VCC powered from a separate external 5V/2A supply, not from the Pi's 5V rail Common ground: yes, relay module GND tied to Pi GND Wiring: Relay IN1 → Pi GPIO17 (physical pin 11) Relay VCC → external 5V supply Relay GND → external supply GND, also tied to Pi GND (physical pin 6) Relay JD-VCC jumper removed (opto-isolation active) Code snippet: python import RPi.GPIO as GPIO import time RELAY_PIN = 17 GPIO.setmode(GPIO.BCM) GPIO.setup(RELAY_PIN, GPIO.OUT) GPIO.output(RELAY_PIN, GPIO.LOW) # activate relay (active-low module) time.sleep(2) GPIO.output(RELAY_PIN, GPIO.HIGH) # deactivate GPIO.cleanup()Libraries/IDE: RPi.GPIO 0.7.1, Python 3.11, run via Thonny and terminal (python3 script.py) Error/log output: No errors or exceptions raised. Script runs to completion. Relay LED indicator does not light up. No audible click.Expected vs actual: Expected the relay to click and switch (LED on module lights up) when GPIO17 goes LOW. Instead, nothing happens — no click, no LED, output stays de-energized. Tests already performed: Measured voltage at GPIO17 with multimeter: reads 0V when script sets LOW, 3.3V when HIGH (pin toggling correctly) Measured voltage at relay VCC: 5.05V present, confirmed external supply working Swapped to GPIO27, same result Tested relay module directly by bridging IN1 to GND with a jumper wire — relay clicked and LED lit, confirming module itself is functional Suspect logic level or ground loop issue between Pi's 3.3V GPIO and 5V relay module optocoupler threshold

Board/platform: ESP32 DevKit V1 (38-pin, CH340 USB driver) Module/component: DHT22 temperature and humidity sensor Power supply: ESP32 powered via USB from PC (5V, ~500mA available) DHT22 powered from ESP32's 3.3V pin Common ground: yes, DHT22 GND connected to ESP32 GND Wiring: DHT22 VCC → ESP32 3.3V DHT22 GND → ESP32 GND DHT22 DATA → ESP32 GPIO4 Code snippet: cpp #include <DHT.h> #define DHTPIN 4 #define DHTTYPE DHT22 DHT dht(DHTPIN, DHTTYPE); void setup() { Serial.begin(115200); dht.begin(); } void loop() { float temp = dht.readTemperature(); float hum = dht.readHumidity(); Serial.print("Temp: "); Serial.print(temp); Serial.print(" Hum: "); Serial.println(hum); delay(2000); }Libraries/IDE: Adafruit DHT sensor library v1.4.4, Adafruit Unified Sensor v1.1.9, Arduino IDE 2.3.2, ESP32 board package v3.0.0 Serial monitor output: Temp: nan Hum: nan Temp: nan Hum: nanExpected vs actual: Expected valid temperature/humidity readings (e.g., 24.5°C, 45%). Instead getting nan on every read. Tests already performed: Verified 3.3V present at DHT22 VCC pin with multimeter Swapped DHT22 module — same result Tried GPIO16 and GPIO17 instead of GPIO4 — same result Increased delay to 2000ms per datasheet minimum sampling rate

Title: Karim Boudiaf / Algeria Description: Hey everyone, glad to be here! Technical level: Technician — I've been doing repair work professionally for about 4 years, though I still consider myself learning in a lot of areas. Skills: Comfortable with motherboard-level laptop repair (reballing, component-level diagnostics), basic soldering/microsoldering, and Windows/Linux troubleshooting. I'd like to get better at reading schematics and diagnosing power-stage issues on smartphones. Main focus: Mostly notebooks and cell phones — that's what comes through my shop most often. I also mess around with small automation/Arduino projects in my free time. Main goal: Mainly to learn from people with more experience, ask technical questions when I hit a wall on a tricky repair, and share schematics or solutions I find useful once I've built up some credibility here. Long term I'd also like to help out newer members with basic diagnostic questions. A bit about me: I run a small repair shop in Sétif, started out self-taught by watching repair videos and taking apart broken devices, then picked up more formal knowledge over the years. Repair work is both my job and honestly my hobby at this point — I like the puzzle-solving aspect of tracking down a fault. Looking forward to being part of the community. Want me to adjust the technical level, country/city, or focus area (e.g., make it about audio gear, boards/automation, or networking instead)?