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AN0254 High Resolution Digital Weigh-Scale Desdign Using Z8 Encore (English, 510 KB)
DWS Schematics (English, 41.3 KB)
Digital Weigh Scale Reference Design - Featuring Zilog's Z8F0812 8bit MCU and Cirrus Logic CS5550 2ch 24bit ADC
- click image to enlarge
This reference design is based on a Z8 Encore! MCU that communicates through one of the serial ports (SPI) with a 24bit Cirrus Logic ADC (CS5550).
The load cell output voltage is passed through a Low Pass Filter to suppress any high frequency noise, and then fed into the ADC. The programmable Gain Amplifier integrated into the ADC scales the measured voltage, further reducing the BOM cost while maintaining a high level of precision.
Essential in this design is that the load cell excitation voltage and ADC reference voltage are derived from the same supply voltage, providing a ratiometric voltage lock that avoids loss of accuracy due to supply voltage variations.
The output of the ADC is displayed on a 8x1 LCD. Software features of the design are TARE, COUNT and CALIBRATION.
Z8 Encore! MCU Features
- 20MHz Core, Register-to-Register architecture
- Up to 64KB FLASH and 4KB SRAM
- 4x 16-bit Timers incl. PWM
- Two 9-Bit UARTs with IrDA
- SPI and I2C Ports
- 3x DMA channel
- On-Chip Debug
- In-Circuit & In-Application Flash Programming
- Voltage BrownOut & WatchDog Timer
- 20 to 80-pin Packages
CS5550 ADC Features
- Output word rate: 2.44 - 4 kSps
- 24-bit A/D registers on both channels
- Channel 1: 13 ENOBs
- Channel 2: 10 ENOBs
- Power consumption: <12 mW
- Adjustable input range on channel 1
- Ground-referenced signals with single supply
- On-chip voltage V reference: 2.5 V (typ 25 ppm / °C)
- On-chip temperature sensor
- Power supply configurations
- VA+ = +5 V
- AGND = 0 V
- VD+ = +3.3 V to +5 V
- Offset and gain calibrations on both channels