Air Pressure Sensors

• Capacitive (one plate moves in response to pressure changes)
• Inductive (a coil or core moves in response to pressure changes)
• Piezoelectric (a piezo crystal deforms in response to pressure changes)
• Motorola Pressure Sensors

MPX5010 Integrated Pressure Sensor:

• Pressure range (0 - 10 kPa)
• Output voltage (0.2 - 4.7 V)
• On-chip temperature compensation, calibration, and signal conditioning
• Various packages and types (gauge or differential):

  

  

• Chip design:

  

Interfacing an MPX Sensor to the BASIC Stamp:

• Analog voltage output from MPX ... need A/D converter.
• ADC0831 Serial A/D (with multiplexer option)
  • 8-bit analog to digital converter
  • synchronous serial output
  • use clock signal sent by BASIC Stamp
  • pin connections:

    

• Use the PULSOUT routine to "clock" the A/D converter.

PULSOUT Pin, Period

where:

• Pin is I/O pin the circuit is connected to.
• Period specifies the duration of the pulse. The unit of time depends on the Stamp processor speed (BS2/BS2e: 2 microseconds; BS2sx: 0.8 microseconds).

PULSOUT sets the pin to output mode, inverts its state, waits for the specified "period", and then returns the pin to its original state.

• Use the SHIFTIN routine to read the synchronous serial data from the A/D converter.

SHIFTIN Dpin, Cpin, Mode, [ Variable {\Bits} {, Variable {\Bits}...}]

where:

• Dpin is I/O pin connected to the serial device's data output.
• Cpin is I/O pin connected to the serial device's clock input.
• Mode specifies the order in which serial bits are arranged and the relationship of clock pulses to valid data (see manual).
• Variable is used to store incoming bits.
• Bits specifies how many bits to input (optional: default=8).

'{ $STAMP BS2 } adcbits VAR BYTE cs CON 0 '0831 "chip select" pin clk CON 1 '0831 clock pin d0 CON 2 '0831 data pin loop: HIGH cs 'set CS pin high LOW cs 'set CS pin low ... starts conversion LOW clk 'clock pulse needs to start low PULSOUT clk, 210 'clock pulse tells 0831 to start on next pulse SHIFTIN d0, clk, MSBPOST, [adcbits\8] 'MSBPOST: msb first, sample bits after clock pulse DEBUG home DEBUG "8-bit binary value: ", bin8 adcbits PAUSE 100 GOTO loop