The scenario
An AT89S52-based 16-relay control board using PCF8574 I2C I/O expanders and ULN2803 Darlington arrays to drive relays while minimizing MCU pin count.
What is in this drawing
Read the decisions behind it.
01
Used PCF8574 to convert I2C to 8-bit parallel output, reducing microcontroller I/O usage.
02
Integrated ULN2803 with common freewheeling diode connection to simplify relay coil protection.
Ideal for home automation, industrial control, and prototyping requiring high relay count with limited MCU pins.
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