The Smart Relays HAT is ideal solution for mission critical projects where you have to be 100% sure that your system works as expected. HALL effect sensors on relay outputs monitor the load current in real time. Not only you can be sure that your loads operate within specified parameters, but you can also measure the load power and you can limit the load current to any value from 1 to 10A.
Four universal inputs can read temperatures from 10K thermistors, dry contact or opto-isolated 0-24V signals.
Stackable to 8 layers, the Smart Relays card can add up to 32 relays and 32 analog/digital inputs to each Raspberry Pi in a very compact form factor.
Pluggable connectors make the card easy to use when multiple cards are stacked up. All relays have Normal Open and Normal Close contacts and can switch up to 10A/240VAC.
COMPATIBILITY
The Smart Relays card is compatible with all Raspberry Pi versions from Zero to 5. All stacked cards 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.
POWER REQUIREMENTS
The card operates from 5V or 10-24V power supply. In both cases it provides 5V and up to 5A to Raspberry Pi. The relay coils are also powered from the 5V. The card draws less than 50mA with all relays off. Each relay needs about 80 mA to turn on.
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.
RESET PUSHBUTTON
Shutting down the Raspberry Pi by turning off the power can result in SD Card failure. To prevent this, a shutdown command needs to be used before power cut-off. But this requires a monitor, keyboard and mouse connected to the Pi.
A momentary on push button installed at the edge of the board provides a convenient way to shut down the Raspberry Pi. The button is read by the local processor, which can be programmed to signal the Raspberry Pi by setting low pin 37 of the Raspberry Pi GPIO connector (GPIO26). You can also read the status of the pushbutton from the I2C interface. You need to write a script which monitors this pin, and if pressed for more than a desired time, issues the shut-down command.
CARD LAYOUT
ELECTRICAL SPECIFICATIONS
- Power Supply: 5V/8A pluggable connector with reverse polarity protection
- On board resettable fuse: 3A
- Opto-isolated Digital Inputs:
- Input Forward Current: Typical 5 mA, maximum 50 mA
- Low Voltage Input Series Resistor: 2.2K
- High Voltage Input Series Resistor: 120K
- Isolation Resistance: Minimum 1012 Ω
- Relays: NO/NC contacts, 8A/240 VAC-24 VDC
MECHANICAL SPECIFICATIONS
RELAY SELF TEST
The card can be tested before installation by running a simple command from the command line. The card will cycle each relay on and off at 0.5 seconds interval. The clacking noise of the relays and the lighting of the LEDs will assure that all relays are functioning.
RS485/MODBUS port
A standard RS485 transceiver permits the Raspberry Pi to communicate using any protocol including MODBUS, PROFIBUS, camera PTZ control, etc. The transceiver can be driven either from the Raspberry Pi serial port, or directly from the local processor. Install the jumpers 485-TX and 485-RX on connector J3 to drive the port from Raspberry Pi. Install the terminator jumper 485-TERM if the card is last on the RS485 chain.
EXTENDED FUNCTIONS OF THE INPUT PORTS
- Transition counters to 4kHz on all inputs
- Input counters with cumulative or PPS (pulse per second) reading up to 4kHz
- 2 x Quadrature encoder inputs reading up to 4000 PPS
- PWM inputs on each channel, reading both the fill factor and the frequency
- 1% resolution on PWM inputs up to 100Hz, 5% resolution up to 500Hz.
