This is I2C bus relay board. The board for remote 8-relay expander for I2C bus based on PCF8574A. Making it ideal as relay expander for I2C bus.
The PCF8574A is the I2C bus controller which talks to microcontroller and then takes commands to the relays. The PCF8574A supports 100kHz bus frequency.
The board is addressed by 3 jumpers to make 8 different addresses. So that 8 boards can be connected together on one bus. Moreover 16 boards can be connected together on one bus when they have 16 different addresses. By this way, 8 boards of the PCF8574A and 8 boards of the PCF8574 can be connected together on one bus. Because the PCF8574A doesn't have same address as the PCF8574.
The board has inverse polarity protection circuit to prevent damage from a mistake of connection. And There is an LED to show status of the input voltage.
The relays also draw power from I2C bus input power supply. So that, the relays don't want another input voltage for them. They have contact rating 0.5A/120Vac, 0.15A/48Vdc and 1A/30Vdc.
Because the I2C bus controller and relays use the same one input voltage VCC. Even though the I2C bus controller can operate at voltage between 2.5V and 5.5V and the relays can operate at voltage between 3.5V and 5.5V. But the board operates at voltage between 4.5V and 5.5V. Because relay drivers drop a part of voltage. However the board works well at standard 5V.
Board is designed for small size, the PCB size is 81.45x34.79mm.
- 8 Relays
- PCF8574A I2C bus I/O expander
- 100kHz I2C bus frequency
- Address by 3 jumpers for use of up to 8 addresses
- Up to 16 boards on one bus
- Operating voltage 4.5V-5.5V
- Inverse polarity protection circuit
- Compatible with almost microcontrollers
- No need another input voltage for relay coils
- Contact rating 0.5A/120Vac,1A/30Vdc,0.15A/48Vdc
- Small board, PCB size 81.45x34.79mm