This project is a low-voltage controller board for a dental suction/vacuum pump system. The pump motor is a RINGBO 3-phase 220 V motor, about 1.6 kW / 7.5 A, driven by a Yaskawa GA500 VFD. The currently installed drive is GA50C2010EBA, and the planned replacement drive is GA50UB010EBA. The PCB being designed is not a direct motor power board; it is a 24 V control board that supervises sensors, safety inputs, display, solenoid flushing, alarms, and VFD commands.
Intended Use
Dental cabinet suction/vacuum control for saliva evacuation. Prototype/control electronics design; final product will need safety/EMC review before use around patients or in a clinical environment.
What the Device Should Do
Measure vacuum level continuously.
Increase pump speed when vacuum falls below the setpoint.
Reduce pump speed or idle when vacuum is sufficient.
Stop the pump on high liquid level or over-temperature.
Run a flush sequence: stop motor, wait about 40 s, open 24 V solenoid for about 20 s, then restart motor.
Show vacuum, pressure, temperature, motor status, alarms, and setpoints on a local display.
Allow manual reset after over-temperature or critical fault.
Main Features
24 VDC control power input.
STM32 microcontroller as the main controller.
Isolated RS485/Modbus interface to Yaskawa GA500 VFD.
Hardware RUN/STOP or enable output to VFD.
Analog 4-20 mA sensor inputs for vacuum and air/pressure sensing.
PT100 temperature inputs via RTD converter.
Float switch digital inputs for tank level.
24 V low-side MOSFET outputs for solenoid valve and alarm lamp/buzzer.
I2C OLED display.
Debug/programming connector.
System Architecture
Diagram
Hardware Subsystems
Power: 24 V input, fuse/reverse/surge protection, 5 V buck, 3.3 V logic rail.
Controller: STM32G4 MCU with watchdog enabled in firmware.
VFD interface: isolated RS485 preferred for speed command and status; hardware run/stop output retained for fail-safe behavior. Target drive is Yaskawa GA500 GA50UB010EBA, using RS485 D+/D-/AC for MEMOBUS/Modbus and a configurable digital input such as S1/SC for RUN permissive after parameter confirmation.
Sensor inputs: 4-20 mA loops converted to MCU ADC voltage through precision shunts and RC filtering.
Temperature: PT100 3-wire sensors handled by MAX31865 RTD-to-digital converters over SPI.
Digital inputs: float switches with pull-ups/pull-downs, filtering, ESD/transient protection.
Outputs: protected 24 V low-side MOSFET drivers with flyback protection for inductive loads.
User interface: SSD1306-class I2C OLED display and buttons/encoder to be added in the next revision if required.
Interfaces and Connections
J24VIN: 24 VDC input.
JVFD/J2: GA500 interface. J2 Pin 1 = RS485_A to GA500 D+, J2 Pin 2 = RS485_B to GA500 D-, J2 Pins 3-4 = isolated dry contact for GA500 RUN/ENABLE input, expected S1/SC or equivalent after confirming drive parameters. AC/shield reference may need a fifth terminal or shield landing if required by the final wiring harness.
JAIN: 4-20 mA vacuum/pressure sensor loop inputs.
JRTD: PT100 3-wire sensor connectors.
JDIN: float switch inputs.
JOUT: 24 V solenoid and alarm outputs.
Display: I2C OLED module.
Debug: SWD connector.
Power and Runtime Expectations
The board is externally powered from 24 VDC. It does not power the 1.6 kW motor directly. Estimated control-board load is below 500 mA at 5 V, excluding external 24 V solenoid/alarm loads.
Power Tree and Power Budget
Table
Rail
Load
Estimated Current
24 V
Solenoid output, external
TBD by valve rating
24 V
Alarm lamp/buzzer, external
TBD by lamp rating
5 V
OLED/display and support
~50-150 mA
3.3 V
STM32 MCU
~50-100 mA peak
3.3 V
RS485, MAX31865, analog front end
~50-150 mA peak
Initial regulator target: 24 V to 5 V buck rated >=1 A, 5 V to 3.3 V regulator rated >=300 mA. Recalculate when final display, sensor count, and output loads are known.
Manufacturing and Assembly Expectations
Prototype PCB with industrial-style screw terminal blocks and clear separation between field wiring, sensor inputs, communication, and logic. The board shall not route mains or motor phase power.
Firmware-Relevant Hardware Requirements
Closed-loop vacuum control using setpoint and hysteresis/PID-like speed command.
RS485 Modbus communication to VFD.
Sensor fault detection: 4-20 mA under-range/open-loop, over-range/short, PT100 fault.
Watchdog and safe outputs on boot/fault.
Manual alarm reset.
Flush sequence timing.
Physical Design Expectations
Board size TBD. Use terminal blocks on board edges, keep VFD/field wiring away from MCU/analog input area, and provide mounting holes.
Important Design Decisions
Use the Yaskawa GA500 as the motor power stage; do not drive the 1.6 kW motor directly from this PCB.
Current drive GA50C2010EBA is a 200/240 V class three-phase-input GA500 unit; planned replacement GA50UB010EBA is a 240 V single-phase-input GA500 unit rated 3 HP / 9.6 A Normal Duty or 2 HP / 8 A Heavy Duty. The control PCB remains low-voltage and does not route VFD input or motor phase power.
Replace PLC/HMI with a microcontroller-based controller plus simple display.
Prefer isolated RS485/Modbus over analog 0-10 V for VFD command and diagnostics.
Keep hardware interlock/run-stop independent from software speed command.
Assumptions
Control supply is 24 VDC.
Sensors are 4-20 mA loop style.
PT100 sensors are 3-wire.
VFD will be configured to accept RS485/Modbus commands.
GA500 terminal and parameter assignments must be confirmed on the actual GA50UB010EBA before energizing the motor: D+/D- polarity, serial format, node address, speed command source, RUN command source, and digital input polarity.
Solenoid valve and alarm are 24 VDC loads.
Change Notes
Initial requirements extracted from user photos and discussion.
Architecture changed from PLC/HMI concept to custom MCU board with display.
User clarified existing VFD is GA50C2010EBA and intended replacement is GA50UB010EBA; project updated to target GA50UB010EBA while preserving GA500-compatible low-voltage interface.
Controller board for a dental suction vacuum pump system using a 24 V low-voltage control board, VFD motor drive interface, 4–20 mA vacuum sensing, float/temperature safety inputs, solenoid flush output, alarm output, and local display.
Properties
Properties describe core aspects of the project.
Pricing & Availability
Distributor
Qty 1
Arrow
$12.42–$16.56
Digi-Key
$6.17–$6.28
HQonline
$8.66–$8.89
LCSC
$13.14–$14.74
Mouser
$24.89–$25.05
TME
$5.26
Verical
$13.34–$19.50
Controls
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