Controller & field wiring

This page is for the field technician doing the install, and the developer who needs to know what the copper actually is. It covers the ModBerry controller, every terminal, the parts list, how RISER ties into three ages of boiler, and the safety chain you must never touch. Read it alongside the System blueprint — the tags here (S1, R1, SF2…) are the boxes on that drawing.

Working drawing, not for construction without field verification. Confirm polarity, part numbers, and terminal assignments on the actual unit before you energize anything.

The controller: ModBerry 500 CM4

The edge controller (C1) is a ModBerry 500 CM4 (TECHBASE) — a Raspberry Pi Compute Module 4 in an industrial, DIN-rail enclosure. One box carries everything RISER needs:

• Analog inputs for the 4–20 mA temperature and pressure transmitters,
• a thermocouple input for the flue,
• RS-485 for the onboard sensor module and the boiler’s own controller,
• a digital output that drives the interposing relay,
• and LTE for the backhaul.

It runs Debian + systemd, and the RISER edge agent is the program on it. The agent’s control loop and safety interlocks run on this box, not in the cloud.

Fallback controller. Where the ModBerry doesn’t fit, the design drops in a Revolution Pi Connect 5 plus AIO + DIO modules, an external 4G router, and a UPS. The RevPi reads RTDs natively but costs more per unit. Both are built against the same IODriver interface, so the agent code does not change — see From code to copper.

Terminal map

Wire the controller to these terminals. Physical IDs (AI1, DO1, TC1) are what the installer lands wire on; the config IDs (ai0, do0, tc0) are what the code uses — the mapping is in From code to copper.

Terminal	Direction	Signal	Lands
AI1	in	4–20 mA	Supply water temp (S1)
AI2	in	4–20 mA	Return water temp (S2)
AI3	in	4–20 mA	Steam pressure (S3, steam only)
AI4	in	4–20 mA	Outdoor air temp (S4)
TC1	in	Type-K	Flue gas temp (S5)
RS-485 A/B/G	in/out	Modbus RTU	Onboard sensor module + boiler controller (B2)
DO1	out	24 V	Interposing relay coil (R1)
PWR	in	24 VDC	From the DIN PSU / UPS
ANT	in	RF	LTE antenna (N1)

Bill of materials

Keyed to the tags on the blueprint. This is the shopping list per building.

Field sensors

Tag	Component	Part / detail	Signal	Connects to
S1	Supply water temp	M12TXSS RTD probe + 4–20 mA transmitter	4–20 mA	Controller AI1
S2	Return water temp	M12TXSS RTD probe + 4–20 mA	4–20 mA	Controller AI2
S3	Steam pressure	Dwyer 616KD + diaphragm siphon (steam only)	4–20 mA	Controller AI3
S4	Outdoor air temp	Outdoor RTD transmitter (weather-reset)	4–20 mA	Controller AI4
S5	Flue gas temp	Tempco TPW00036 thermocouple	Type-K	Controller TC1

Edge controller & power

Tag	Component	Part / detail	Signal	Connects to
C1	Edge controller	ModBerry 500 CM4, runs the RISER agent	all I/O + LTE	Hub for everything
P1	AC service feed	120 VAC building supply	120 VAC	PSU P2 + switched line to R1
P2	DC power supply	24 VDC DIN-rail PSU	24 VDC	UPS P3, controller PWR
P3	UPS	Battery ride-through	24 VDC	Controller PWR

Actuation, boiler & native safety

Tag	Component	Part / detail	Signal	Connects to
R1	Interposing relay	Briidea 24 V coil → 120 V SPDT contact	24 V coil / 120 V	Driven by DO1, switches B1 call-for-heat
B1	Boiler / burner	Existing plant under control	—	Call-for-heat from R1, gated by SF chain
B2	Boiler Modbus controller	Modern boilers only	RS-485	Controller RS-485 (read + write)
SF1	Aquastat (high limit)	Native safety, never bypassed	line	Series burner-enable string
SF2	Low-water cutoff (LWCO)	Native safety, never bypassed	line	Series burner-enable string
SF3	Pressure relief valve (PRV)	Native mechanical safety	—	Boiler vessel / burner

Connectivity & cloud

Tag	Component	Part / detail	Signal	Connects to
N1	Cellular antenna	External LTE antenna	RF	Controller ANT
N2	Carrier SIM	T-Mobile data SIM	—	Controller modem
N3	LTE network	Carrier cellular	RF / IP	Internet
N4	Internet	Public network	HTTPS	Backend K1
K1	RISER backend	FastAPI application	HTTPS	Receives telemetry, serves commands
K2	Database	PostgreSQL	SQL	Backend K1
K3	Operator web app	Browser dashboard	HTTPS	Backend K1

Boiler integration: three ages of boiler

RISER meets the boiler where it is. How you connect depends on how modern the boiler’s own controls are.

Boiler age	How RISER connects	Control you get
Modern	RS-485 Modbus straight to the boiler controller (B2). Reads status, writes setpoints.	Full read + setpoint write
Older	Interposing relay (R1) to the aquastat terminals, plus RISER’s own sensors for visibility.	On/off + rich monitoring
Really old	Interposing relay (R1) switches the 120 VAC call-for-heat.	On/off only

In every case RISER adds its own sensors (S1–S5) for visibility — even a really-old boiler gets full telemetry, it just gets simpler control.

The interposing relay (why it exists)

The controller output (DO1) is a low-voltage 24 V signal. The boiler’s call-for-heat is line voltage. The interposing relay R1 bridges the two: the controller energizes the 24 V coil, and the relay’s contact switches the 120 V.

Safety-critical wiring. RISER never switches line voltage from the controller. It only energizes a relay coil. Confirm relay polarity so that energized coil = boiler enabled — the de-energized (power-loss) state must fall back to the boiler’s native controls, heat available.

The native safety chain — never bypassed

The aquastat (SF1), low-water cutoff (SF2), and pressure relief valve (SF3) are the boiler’s own, independent, code-required safeties. They are wired in series as the burner-enable string. RISER’s call-for-heat passes through this string; any one device can shut the burner down on its own.

RISER is wired in addition to, never in place of, the native safety chain. If you find yourself jumpering out an aquastat or a low-water cutoff to make RISER work, stop — that is wrong. The whole design depends on those devices remaining live and independent.

Power & ride-through

120 VAC (P1) → 24 VDC DIN PSU (P2) → UPS (P3) → controller. The UPS gives the controller ride-through so a brief power sag doesn’t reboot it mid-cycle. On a full outage the boiler’s native controls keep heat available regardless of the controller’s state.