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BacBus

BacBus is a free BACnet/IP and Modbus/TCP field utility from Harness Automation. It turns your phone into a building-automation field tool: discover controllers on the jobsite network, browse their objects, read live values, and — with a one-time Pro unlock — write points and command overrides. No laptop, no gateway, no proprietary software.

BacBus is the free companion to GEM (Global Environment Manager), our flagship building-automation platform.

What BacBus does​

  • Discover — broadcast a BACnet Who-Is and list every device that answers, with device ID, vendor, and IP. Where some scanners come back empty, BacBus pulls the full object list.
  • Read — browse a device's objects and poll live present-values: setpoints, sensor readings, status flags, units, and object names.
  • Modbus/TCP — connect to any Modbus slave, auto-discover which registers are actually mapped, and read holding/input registers and coils/discrete inputs with selectable data types and word order.
  • Control (Pro) — write present-values, command outputs at a chosen BACnet priority, relinquish stuck commands, write Modbus registers and coils, and export readings to CSV.

How it works​

BacBus speaks the two protocols very differently — because the protocols themselves are built on different ideas. Your phone is the client in both cases; what changes is how it finds and talks to equipment.

BACnet/IP — broadcast discovery​

BACnet is self-describing and discoverable. BacBus sends a single Who-Is broadcast on the subnet; every controller that hears it answers I-Am with its device ID and vendor. You pick a device, BacBus reads its object list, then polls the present-values you care about — no addresses or register maps to know up front.

Modbus/TCP — point-to-point​

Modbus has no discovery at the protocol level — it's a direct connection to one slave at a known IP and port, with no equivalent of BACnet's Who-Is. BacBus fills that gap: once connected, it auto-probes which registers are actually mapped across every address space and surfaces them for you, so you don't need the register map up front. Read them with the data type and word order you choose. That slave is often a TCP gateway fronting serial (RS-485) RTU devices.

Who it's for​

BacBus is built for the people who work on real building systems — controls integrators, BAS technicians, and commissioning engineers. Everything is designed for one-handed use on a phone, on cellular or site Wi-Fi, standing in front of a panel.

Free vs. Pro​

Discovery, object browsing, live reads, and all Modbus scanning are free, forever — no account, no sign-in. A single one-time purchase (not a subscription) unlocks the power-user extras: writing values, relinquishing priority, and CSV export. See BacBus Pro for the full breakdown.

Requirements​

BacBus talks directly to controller hardware on your local network. It needs real BACnet/IP or Modbus/TCP equipment on the same subnet/VLAN as your phone to show data — there is no cloud or sample data. On a network with no such equipment, a scan will correctly return nothing.

  • iOS 14 or later (App Store)
  • Android — coming soon to Google Play

Next steps​