RX23E-B Digital Load Cell Tiny Board Reference Design

The RX23E-B Digital Load Cell Tiny Board Reference Design is a compact and efficient solution for digital load cell design that utilizes the RX23E-B 32-bit microcontroller. This microcontroller integrates a high-speed, high-precision analog front-end (AFE), which negates the necessity for a dedicated AFE, thereby minimizing the board size.

Since the load cell is integrated with the board on which the AFE or MCU is mounted, the board must be compact. The RX23E-B combines an AFE and MCU on a single chip, eliminating the need for a dedicated AFE and making it suitable for board miniaturization. For this reference design, we designed a tiny 22mm × 16mm board. In addition to the RX23E-B, this compact board includes the RAA788155 RS-485/RS-422 transceiver. The RX23E-B performs A/D conversion, digital filtering, calibration, and voltage-to-weight conversion. The RAA788155 sends the weight value to the host device via digital communication, such as Modbus.

When developing this reference design, we incorporated this tiny board into the load cell and evaluated the weight measurement error. The gravimetric error is ±0.01%FS. In addition, we evaluated the resolution using a calibration strain generator under conditions of 10 SPS output data rate and 128x PGA gain. We confirmed that the input-referred voltage noise was 23.8nVrms and the peak-to-peak voltage noise was 140nV.