CorePressure. Issue: A (Preliminary)

Transcription

1 CorePressure Issue: A (Preliminary) 1

2 Contents Table of Figures... 2 Introduction... 3 Electrical... 4 Further Information... 5 Appendix A: Sensor Expansion Interface... 6 Table of Figures Figure 1. CorePressure module Figure 2. SExI device foot print

3 Introduction CorePressure is a half-width SExI-compliant digital pressure sensor using the Bosch Sensortec BMP085. This module can measure barometric pressure from 300 to 1100 hpa with an accuracy of 0.03hPa. The BMP085 provides access to its internal register using the two wire I2C protocol. CorePressure provides a convenient hardware platform in a standard footprint to allow rapid sensor prototyping. For ultimate ease the CorePressure module is supported for in CoreBASIC providing a simple software interface into the powerful sensing capabilities of this module. Features SExI-compliant footprint. 300 to 1100 hpa measurement range. 12 µa Current consumption in ultra-high resolution mode (1 sample / sec at 25 C). Simple I2C interface. Supported in CoreBASIC using the CORE-PRESSURE driver Figure 1. CorePressure module. 3

4 Electrical CorePressure uses the SExI interface for rapid integration into a hardware platform. The communications pins (I2C) from the BMP085 are taken to the I2C SExI pins for convenient access. CorePressure uses the 3V3 rail and not the 5V rail. The two digital pins XCLR and EOC from the BMP085 are routed (via jumpers) to the AN and DIO pins of J1. The jumpers are left open circuit by default. Left Con Description Right Con Description AN XCLR (NC default) Rx NC SDA I2C Data Line 5V0 NC SCL I2C Clock Line 3V3 3.3V power supply rail DIO EOC (NC default) 0V Power return path Table 1. CoreLight SExI Pin Information The pull-up resistors, R1 and R2, are not fitted by default. You will need to fit R1 and R2 if the external development platform does not have pull-up resistors on the I2C bus. Note: if using CorePressure with the SenseCore module the pull up resistors are located on the SenseCore. A thick white stripe provides a clear visual indication of the correct orientation of the sensor when installing it into the SExI socket on the SenseCore. Make sure that you orient the sensor so that the white stripe on the sensor locates with the white stripe on the SExI socket. 4

5 Further Information Example programs written in C and CoreBASIC can be found at Here is an example program for the CorePressure sensor in CoreBASIC. 10 ' Demonstration code for the CorePressure sensor, which is 20 ' a Bosch Sensortec BMP ' 40 ' Written by Paul Curtis of Rowley Associates. 50 ' You're free to do what you like with this program. 60 ' 70 INSTALL "BOSCH-SENSORTEC-BMP085" AS BAROMETER 80 ' 90 ' Today's pressure is 1014 hpa at sea level, which is pascals 100 BAROMETER.ORIGIN = ' 120 ' Use a high-precision sample 130 BAROMETER.RESOLUTION = ' 150 ' Sample the pressure senor once, and use that throughout 160 PRESSURE = BAROMETER.PRESSURE 170 ' 180 ' Do some calculations 190 PRINT "Measured pressure is "; PRESSURE; " pascals" 200 PRINT "...and that's "; PRESSURE / 100; " hpa (millibars)." 210 ' 220 PRINT 230 PRINT "With pressure of "; BAROMETER.ORIGIN; " pascals "; 240 PRINT "at sea level," 250 PRINT "I calculate that my height above "; 260 PRINT "sea level is "; BAROMETER.HEIGHT; " meters." 270 ' 280 ' Do some more calculations PRINT 300 PRINT "For the curious, that's "; PRESSURE * ; " mmhg"; 310 PRINT " and "; PRESSURE * ; " inhg." 320 ' 330 END 5

6 Appendix A: Sensor Expansion Interface The SolderCore range of sensors use a standard interface called SExI (Sensor Expansion Interface). This standard allows a single development hardware platform to be used to evaluate a range of sensors. Referring to Figure 2, a SExI device is comprised of two sections. Each section has common power pins consisting of 3.3V, 5V and 0V. If a sensor uses only SPI, only the top four rows of pins are required. For I2C based sensors, only the bottom four pins are required, in both instances the sensor foot print can be halved. The SExI footprint provides for sensors that use simple UART connections. The Tx and RX pins are located on the right hand side of the module. The DIO line can be used as a digital input of output line. Many sensors use interrupt lines, to inform the external electronics/processor that an even has occurred. In most instances the interrupt line is taken to DIO. AN can be either a Digital IO or an Analog output pin. Sensors that output readings as an analog signal use this pin. The SenseCore shield routes this pin to the ADC pins to the SolderCore / Arduino headers. The right hand connector is marked with a thick white bar to easily identify it. Figure 2. SExI device foot print. 6