It is burglar alarm expansion unit with 8 balanced and 1 unbalanced (tamper) ports. Each port is able to connect to any commercial PIR, microwave sensor or reed switch. It's primarily made as expansion unit to OHS gateway, for which the example sketches are on GitHub. But it can work as standalone alarm unit, or it can be made to report the sensors states to any other base station via wired RS485 or radio RFM69/95. It's basically an Arduino compatible board with ATmega 328P running at 16MHz@3.3V.

• Size 10 x 5 cm.
• Green LED as power on indication.
• DC 11 - 14V with fuse and over voltage protection.
• Battery OK and Power Off signals via 4 pin power connector. Suited for Meanwell PSC-35A-C power supply. With this power supply and battery, it can act as UPS.
• Power cable included, JST-XH-4 2.54mm 4pin connector with 40cm cable.
• 8 analog(balanced) ports, switchable to unbalanced by software. 2 x 8 2k2 balancing resistors included. 12V balanced terminal output supply is fused with separate 400mA resetable fuse.
• 1 digital(unbalanced) opto-issolated port for box enclosure (tamper).
• Optional relay with terminals (Input, Normally Open, Normally Closed, and GND), NC, NO outputs of the relay can be either 12V, or provided by input terminal. Relay can act as Siren/Horn relay or general purpose output. 12V relay output is fused with separate 200mA resetable fuse.
• 2 unpopulated MCU pins, together with ground, available via I/O header.

Communication options are:

• RS485 for serial over twisted wire pair, with terminator pins and termination resistor. Library is provided on GitHub.
• RFM69CW-868/915 for wireless, long reach. Footprint ready also for RFM95 LoRa. Also with optional spring or rubber antenna. Using LowPowerLab, or any other RFM69 library.
• Both RS485 and RFM69CW-868/915
• None :)

Programmable via standard FTDI programmer. RS485 version is programmable only via ISP(6-pin, using USBasp, another Arduino, or other programmer) as hardware serial is connected to RS485 chip, use upload via programmer in Arduino IDE.

Example sketches on GitHub are prefixed with OHS_2-extesion, then board revision 1_0, and board option like RS485_Siren. For example: OHS_2-extesion_1_0_RFM69_Siren

Balanced sensors can be attached using following scheme. As can be seen from below PIR sensor example, at least 3 wires are needed for operation. The board provides 12V and GND for the sensor operation, and after the resistor cascade, input is brought back to the expansion board. Standard wired 2k2 1/4w resistors for the balanced cascades are included. Unbalanced sensors, like reed switches or any passive sensor, can be connected directly without resistor cascade using just 2 wires. That is connected to GND, and any of the board input terminal. However balanced connection are more secure, and provide tamper detection to the wiring and sensor itself.