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sensor:pcf857x [2026/05/14 19:59] – [Wiring with relay modules] vamsansensor:pcf857x [2026/05/15 01:03] (current) – [PCF857x Vcc and Vdd] vamsan
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 The [[arduino:display_lcd#i_c_lcd_adapter|I²C LCD adapter]] utilizes the PCF8574.   The [[arduino:display_lcd#i_c_lcd_adapter|I²C LCD adapter]] utilizes the PCF8574.  
  
-**Main Control & Power Header** +==== PCF857x Pinout ====
   * **VCC:** Power input. Connects to **3.3V or 5V** to match your microcontroller's logic levels.   * **VCC:** Power input. Connects to **3.3V or 5V** to match your microcontroller's logic levels.
 +  * **VDD:** Power input. Connect the external hardware power to **3.3V or 5V**.
   * **GND:** Common ground reference.   * **GND:** Common ground reference.
   * **SDA:** Serial Data line for I²C communication.   * **SDA:** Serial Data line for I²C communication.
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   * **Port 1** (PCF8575 only, P10 to P17): The second group of 8 quasi-bidirectional GPIO pins.   * **Port 1** (PCF8575 only, P10 to P17): The second group of 8 quasi-bidirectional GPIO pins.
  
 +==== PCF857x Reverse side of the module ====
 +{{ :sensor:pcf8575_2.png |PCF857x I/O Expander chip/modul reverse side}}
 +
 +==== PCF857x Vcc and Vdd ====
 +^Pin^Function^Typical Target^Voltage Role|
 +^VCC|Microcontroller (Logic) Side|Connect to your MCU's power pin (e.g., 3.3V or 5V).|Sets the operating reference voltage for the I²C communications line (SDA/SCL).|
 +^VDD|Peripheral (Device) Side|Connect to the external hardware power (e.g., 5V).|Directly sets the high voltage logic level of the 16 target output/input pins (P00–P17).|
 +
 +**The Crucial Condition: Check the Solder Jumper**
 +
 +For this dual-voltage (3.3V/5V) configuration to work safely, the onboard VCC-VDD solder jumper must be open (disconnected).
 +  * If **the jumper is open**, the module’s built-in level shifters are enabled. The I²C lines (SDA/SCL) will communicate securely at 3.3V with your microcontroller, while the 16 I/O pins (P00–P17) will operate at 5V, since the expander logic runs at the VDD level.
 +  * If **the jumper is bridged**, VCC and VDD are connected together. Applying 3.3V to VCC and 5V to VDD can create a short circuit, leading to overheating and <color red>possible damage to your microcontroller</color>.
 +
 +==== PCF857x module's addressing ====
 +To assign a specific 7-bit hex address, use a soldering iron to connect the center pad of each group to either GND or VCC.
 +
 +|<100%>|
 +^A2 Status^A1 Status^A0 Status^Resulting Binary Offset^Hex I²C Address|
 +^GND (Open)|GND (Open)|GND (Open)|000|0x20 (Default)|
 +^GND (Open)|GND (Open)|VCC (Bridged)|001|0x21|
 +^GND (Open)|VCC (Bridged)|GND (Open)|010|0x22|
 +^GND (Open)|VCC (Bridged)|VCC (Bridged)|011|0x23|
 +^VCC (Bridged)|GND (Open)|GND (Open)|100|0x24|
 +^VCC (Bridged)|GND (Open)|VCC (Bridged)|101|0x25|
 +^VCC (Bridged)|VCC (Bridged)|GND (Open)|110|0x26|
 +^VCC (Bridged)|VCC (Bridged)|VCC (Bridged)|111|0x27|
 +
 +==== PCF857x using I/O pin ====
 **Sinking Current (Output LOW / Connecting to Ground)** **Sinking Current (Output LOW / Connecting to Ground)**
  
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 {{ :sensor:pcf857x_wiring_1.png |PCF8575 I/O How to Correctly Wire Components}} {{ :sensor:pcf857x_wiring_1.png |PCF8575 I/O How to Correctly Wire Components}}
  
-==== Wiring with relay modules ====+{{page>:tarhal}} 
 + 
 +==== PCF857x wiring with relay modules ====
 Connecting optocoupled relay modules to the PCF8575 is a common practice, but it requires strict electrical care. Because of the chip's asymmetrical quasi-bidirectional ports, a mistake in how you trigger the relay will prevent it from working entirely. Connecting optocoupled relay modules to the PCF8575 is a common practice, but it requires strict electrical care. Because of the chip's asymmetrical quasi-bidirectional ports, a mistake in how you trigger the relay will prevent it from working entirely.