Differential Pressure Gauge Sensor
The Digilent Pmod DPG1 (Revision A) is a differential pressure gauge. With NXP's MP3V5010DP piezoresistive transducer and Texas Instrument's ADCS7476 12-bit Analog-to-Digital Converter, you can detect when a change in pressure between the two ports occurs and send digital information to your system board.
Functional Description
The Pmod DPG1 is designed to detect a differential pressure ranging from 0 kPa to 10 kPa. It uses an embedded 12-bit ADC to provide the user with a serial stream of data representative of the measured pressure difference between the two ports on the sensor.
Interfacing with the Pmod
The PmodDPG1 communicates with the host board via the SPI protocol with SPI Mode 0 (CPOL = 0, CHPA = 0). The 12 bits of digital data are sent to the system board in 16 clock cycles with the most significant bit first. For the embedded ADC7476, each bit is shifted out on each falling edge of the serial clock line after the chip select line is brought low with the first four bits as leading zeroes and the remaining bits representing the 12 bits of data. The datasheet for the ADC7476 recommends that for faster microcontrollers or DSPs that the serial clock line is first brought to a high state before being brought low after the fall of the chip select line to ensure that the first bit is valid.
As a differential pressure module, it should be noted that the Pmod can only accept a certain range of pressure differences without damaging the internal piezoresistive silicon. When the Pmod is laid on a flat surface such that the transducer is above the PCB, the top most nozzle is P1 (the receiving nozzle to detect fluctuating pressure) and the bottom most nozzle is P2 (the pressure reference nozzle for P1). The pressure at P1 is recommended to be between 0 and 10 kPa above the pressure present at P2. Pressures outside of this range may cause permanent damage to the device.
The Pmod DPG1 is capable of converting up to 1 MSa per second of 12-bit data, but the transducer response time to a step change of 1 kPa is 1 ms. Smaller changes in pressure will take less time for the transducer to change its output voltage.
Any external power applied to the Pmod DPG1 must be within 2.7 V and 3.3 V to ensure that the on-board chips operate correctly; however, it is recommended that Pmod is operated at 3.3 V since an embedded regulator reduces the 3.3 V down to 3 V for the various embedded components.
Physical Dimensions
The pins on the pin header are spaced 100 mil apart. The PCB is 1.0 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header. The transducer nozzles extend an additional 0.25 inches and the height of the transducer extends 0.375 inches above the PCB.