1300 Henley Court
Pullman, WA 99163
509.334.6306
www.digilentinc.com
PmodDPG1 Reference Manual
Revised August 10, 2016
This manual applies to the PmodDPG1 Rev. A
DOC#: 510-333
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 1 of 4
Overview
The Digilent PmodDPG1 (Revision A) is a differential gauge pressure module. 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.
1 Functional Description
The PmodDPG1 is designed to detect a gauge pressure ranging from 0 kPa to 10 kPa with a piezoresistive
transducer and use an embedded 12-bit ADC to provide the user with a serial stream of data representative of the
measured pressure.
The PmodDPG1.
Features include:
PmodDPG1™ Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 2 of 4
2 Specifications
Parameter
Min
Typical1
Max
Units
Recommended Operating Voltage
3.125
3.3
3.5
V
Maximum Supply Voltage
-
-
5.5
V
Maximum Pressure2
-
-
75
kPa
Minimum Pressure Offset3
0.1
0.24
0.38
V
Sensor Accuracy
-0.54
0
0.54
kPa
Parameter
Value
Units
Communication Protocol
SPI Mode 04
Power Supply Current draw5
10
mA
Sensor Response Time
1
mS
Sensor Bandwidth
500
Hz
Note1 - Data in the Typical Column uses VCC at 3.3V unless otherwise noted
Note2 - Where the pressure at P1 (top nozzle) is greater than the pressure at P2 (bottom nozzle)
Note3 - Output voltage corresponding to a pressure differential of 0 kPa
Note4 - CPOL = 0, CHPA = 0
Note5 - Normal operation with VCC at 3.3V
3 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
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.
To convert the serial data stream back into a corresponding pressure, users may use the following equation:
PmodDPG1™ Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 3 of 4
3.1 What can I Safely Measure with the PmodDPG1?
The recommended pressure differential range for the embedded MP3V5010 on the PmodDPG1 is between 0 kPa
and 10 kPa, so it is ideally suited for applications such as measuring small pressure changes inside a venturi meter,
as a pressure plate to detect when something touches it, or to determine the air pressure exerted by the normal
human lung (presuming you are not a trumpet player or in another field where you need above average lung
pressure). Notably, the PmodDPG1 is not able to measure the air pressure inside of a car or bike tire.
The reference article for the human lung pressure, for those of you that are interested, can be found from the
National Center for Biotechnology Information website here.
Additionally, the PmodDPG1 is only able to measure dry fluids, such as air, as opposed to being able to measure
water pressure.
But what is the lowest pressure that the PmodDPG1 can detect? With an embedded 12-bit ADC that is powered at
3 V, the LSB will have a corresponding voltage of 0.732 mV, but the MP3V5010 has a listed sensitivity of 270 mV
per kPa, or equivalently, 0.270 mV per Pascal. This means an LSB change will not occur until an approximate
change of 3 Pascals of pressure occurs. Based on Wikipedia's list of orders of magnitude of pressure, a U.S. dollar
bill exerts approximately 1 Pascal. Additionally, the lung air pressure difference of a normal breath from a person is
approximately 300 Pascals, so the module is very capable of measuring very small changes in pressure.
3.2 Pinout Table Diagram
Pin
Signal
Description
1
SS
Chip Select
2
NC
Not Connected
3
MISO
Master-In-Slave-Out
4
SCK
Serial Clock
5
GND
Power Supply Ground
6
VCC
Power Supply (3.3V/5V)
The PmodDPG1 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 PmodDPG1 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.
PmodDPG1™ Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 4 of 4
4 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.