Brings to Raspberry Pi all IO's needed for Building Automation Systems. Eight universal inputs can be software selected to process 0-10V signals, read 1K or 10K temperature sensors or dry contact counters. Four TRIAC outputs can drive loads up to 1A at 24VAC. Four 0-10V outputs can control light dimmers. Status LEDs display the state of all outputs. Keep time indefinitely even during power failure using the Real Time Clock with battery backup. Connect up to 16 DS18B20 temperature measurement devices on the 1-Wire interface. Activate the hardware watchdog to monitor and power cycle the Raspberry Pi in case of software lockup. TVS diodes on all inputs protect the card for external ESD, and the on-board resettable fuse protects is from accidental shorts.
DRIVING ADDITIONAL LOADS
Heavy loads of up to 8A and 250VAC can be driven adding one or more 4-RELAYS cards. High DC loads of up to 10A and 250V, with fast response time and unlimited endurance can he driven by adding one or more 8-MOSFET cards.
1-WIRE INTERFACE
Latest version of the HAT has also a standard 1-Wire interface. Up to 16 DS18B20 temperature measurement devices can be connected in parallel. Devices can be accessed from the command line of from the MODBUS interface.
COMPATIBILITY
The card share the I2C bus using only two of the Raspberry Pi’s GPIO pins to manage all eight cards. This feature leaves the remaining 24 GPIOs available for the user. The card is compatible with all Raspberry Pi versions from Zero to 5 and has all the necessary I/Os for your Building Automation projects.
POWER REQUIREMENTS
The card requires a 24VAC/1A external transformer to operate and has to be powered from it's own pluggable connector. The card supplies 5V and up to 3A to the Raspberry Pi on the GPIO bus. A local 3.3V regulator powers the rest of the circuitry. The card needs 50mA to operate.
PLUGGABLE CONNECTORS
All the IO's are connected to heavy duty (8A), 3.5mm pitch pluggable connectors which make field wiring very convenient for installation and debugging.
DIP SWITCH CONFIGURATION
A six position DIP switch is used to select the source of the RS485 port and the position of the card in the stack, if multiple cards are used.

STACKING MULTIPLE CARDS
Up to eight cards can be stacked on your Raspberry Pi. Three positions of the configuration DIP Switch labeled ID0, ID1, ID2 are used to select the stack level. Cards can be stacked in any order.
RS485/MODBUS Port
The card has an RS485 port which can be driven from the Raspberry Pi, or from the local processor. Leave the TX and RX switches in the OFF position to connect the port to the local processor. Set both to ON to connect to USART1 on the Raspberry Pi GPIO connector.
When DIP Switches are ON, Raspberry Pi can communicate with any device with an RS485 interface. In this configuration the card is a passive bridge which implements only the hardware levels required by the RS485 protocol. To use this configuration, you need to tell the local processor to release control of the RS485 bus:
~$ megabas [0] rs485wr 0 0 0 0 0
When DIP Switches are OFF, the card operates as MODBUS slave and implements the MODBUS RTU protocol. Any MODBUS master can access all the card's inputs, and set all the outputs using standard MODBUS commands. A detailed list of commands implemented and parameters addresses can be found on GitHub:
In both configurations the local processor needs to be programmed to release (jumpers installed) or control (jumpers removed) the RS485 signals. See the command line online help for further information.
RS485 TERMINATOR
The last position on the DIP switch is the RS485 line terminator. Set it to ON if the card is last on the RS485 chain.
CARD LAYOUT
ELECTRICAL SPECIFICATIONS
- Power supply: 3.5mm Pluggable Connector, 24V/1A
- Power consumption: 50mA @ 24V
- On board resettable fuse: 1A
-
0-10V Inputs:
- Maximum Input Voltage: 12V
- Input Impedance: 20KΩ
- Resolution: 12 bits
- Sample rate: 500 sps
- Full scale linearity: 0.15%
- Contact closure inputs max. frequency: 100Hz
- 0-10V Outputs:
- Minimum Output Load: 1KΩ
- Resolution: 0.1%
- Full scale linearity: 0.1%
- Triac Outputs;
- Maximum Output Current: 1A
- Output Voltage: 24VAC
MECHANICAL SPECIFICATIONS