LMP91200

The official HydroSense library for the TI LMP91200 PH frontend. Updated: March 26, 2016 7:37 PM By: Ward Prescott

Class

###Constructor LMP91200(int cs) The only argument is the chipselect pin for the device.

Methods

• .begin(void) is used start the SPI bus with the correct settings. Note that the LMP91200 uses SPI mode 3, though most other TI devices use SPI mode 1.

• .setPGA(int PGASet) is used to set the programmable gain amplifier internal to the AFE. Arguments are:

Argument	Description
PGA5	5 Volts/Volt (DEFAULT)
PGA10	10 Volts/Volt

• .setVCM(int VCOMSet) is used to set the reference voltage offset. This setting can be changed if the PH range is within known values that are skewed to acidic or basic. Arguments are:

Argument	Description
VCM_78	Common mode voltage at 7/8 Vcc
VCM_34	Common mode voltage at 3/4 Vcc
VCM_58	Common mode voltage at 5/8 Vcc
VCM_12	Common mode voltage at 1/2 Vcc (DEFAULT)
VCM_38	Common mode voltage at 3/8 Vcc
VCM_14	Common mode voltage at 1/4 Vcc
VCM_18	Common mode voltage at 1/8 Vcc

• .setVOCM(int VOCMSet) is used to select between differential or singled ened output. Arguments are:

Argument	Description
VOCM_VOCM	Differential output (DEFAULT)
VOCM_GND	Singled ended output

Parameters

The class has no public parameters. ##Usage

#include <LMP91200.h>
LMP91200 myLMP(A4);

void setup(){
 myLMP.begin();
 delay(50);
 myLMP.setVCM(0b000);
 myLMP.setPGA(0b0);
 
}

void loop(){
//Read the LMP via an ADC
}

The device works via an SPI bus, so it is imperative that all chip select pins are set to high for other SPI peripherals.

##Notes The LMP91200 is not reccomened for new designs and a suitable replacement is currently being researched.

##Further Work The PGA does not appear to be working on the LMP91200 but further investigation is needed to confirm this.