The Challenge
The client manufactured a fluid control manifold system in which a central controller needed to independently actuate up to 16 solenoid valves. In the existing wired design, a thick multi-conductor harness ran from the controller cabinet to the manifold — expensive to manufacture, prone to connector failures, and difficult to route in tight installations.
The goal was to replace the wiring harness with a wireless module mounted directly on the manifold, controlled over BLE from the main controller. The module also needed to read system pressure from a sensor via SPI, run on a Li-Ion battery pack for at least 24 hours of continuous operation, and fit within the existing manifold footprint (80 × 50mm).
The Process
The design needed to balance three competing demands: the high current draw of 16 solenoid channels, BLE radio sensitivity requirements, and long battery life.
- MCU & BLE: The nRF5340 dual-core SoC was chosen — the network core handles BLE 5.2 while the application core manages solenoid scheduling and sensor acquisition. A custom BLE GATT service exposes valve control and pressure reading to the central controller.
- Solenoid Drive: Two cascaded 74HC595 8-bit shift registers expand a single SPI bus into 16 independent output channels. Each output drives a TBD62083 Darlington transistor array capable of 500mA per channel at 24V — sufficient for the client's latching solenoids. Freewheeling diodes on all outputs handle back-EMF.
- Pressure Sensing: An MS5803-14BA SPI pressure sensor provides 14-bar range with 0.6mbar resolution. The sensor shares the SPI bus with the shift registers via chip select.
- Power: A 2-cell 7.4V Li-Ion pack feeds a TPS54332 buck converter down to 5V (solenoid drive), with a secondary LDO (LM1117) generating 3.3V for the nRF5340 and sensor. The nRF5340's 2.4GHz antenna keep-out area was respected by routing all high-current traces along the board periphery.
Firmware was developed with nRF Connect SDK on Zephyr RTOS. A valve scheduler dispatches SPI shift register updates at 1ms resolution, allowing sequenced or simultaneous valve actuation patterns defined by the BLE central in real time.
The Result
The wireless module successfully replaced the wired harness in field trials. BLE link reliability was excellent — zero dropped commands in 48 hours of continuous testing at 5m range with one concrete wall between controller and manifold. The pressure sensor readings were accurate to within 1.2mbar against a reference gauge.
Battery life measured 31 hours with all 16 valves cycling at a 50% duty cycle — significantly exceeding the 24-hour specification. The module's compact 78 × 48mm PCB fit the manifold mounting footprint with 2mm to spare on each side.
- 16 independent solenoid channels, 500mA each at 24V
- BLE 5.2 with 2Mbps PHY, zero dropped commands in 48h test
- Pressure measurement: 0–14 bar, ±1.2mbar accuracy
- Battery life: 31 hours at 50% valve duty cycle
- PCB: 78 × 48mm, 4-layer
- Wiring harness cost eliminated: ~€120/unit saved