Beaglebone and TMD2771 proximity and ambient light sensor python example


In this article we look at another sensor – this time its the TMD2771 and we will connect it to our Beaglebone and we will have a python example

First lets take a look at the sensor in question

Ambient Light Sensing, Proximity Detection, and IR LED in a Single Optical Module

Ambient Light Sensing (ALS)
—-Approximates Human Eye Response
—-Programmable Analog Gain
—-Programmable Integration Time
—-Programmable Interrupt Function with Upper and Lower Threshold
—-Up to 16 Bits Resolution
—-Very High Sensitivity – Operates Behind Darkened Glass
—-Up to 1,000,000:1 Dynamic Range

Proximity Detection
—-Calibrated to 100mm Detection
—-Eliminates Factory Calibration of Prox
—-Programmable Number of IR Pulses
—-Programmable Current Sink for the IR LED – No Limiting Resistor Needed
—-Programmable Interrupt Function with Upper and Lower ThresholdD

Programmable Wait Timer
—-Wait State – 65mA Typical Current
—-Programmable from 2.72ms to >8 Seconds
—-I2C Interface Compatible Up to 400 kHz (I2C Fast Mode)
—-Dedicated Interrupt Pin
—-3.94 mm y 2.4 mm y 1.35 mm Package
—-Sleep Mode – 2.5 mA Typical

Parts Required

Name Link
Beaglebone BeagleBone Black TI AM335x Cortex-A8 development BB-Black Rev.C
TMD2771 MCU-88 TMD27713 ALS infrared LED optical proximity distance detector module
Connecting wire Free shipping Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire


beaglebone and TMD2771 layout
beaglebone and TMD2771 layout

Code Example

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import smbus
import time
# Get I2C bus
bus = smbus.SMBus(2)
# TMD2771 address, 0x39(57)
# Select enable register 0x00(00), with command register, 0xA0(160)
#		0x0F(15)	Power ON, Wait enable, Proximity enable, ALS enable
bus.write_byte_data(0x39, 0x00 | 0xA0, 0x0F)
# TMD2771 address, 0x39(57)
# Select ALS time register 0x01(01), with command register, 0xA0(160)
#		0xDB(219)	ATime - 101 ms
bus.write_byte_data(0x39, 0x01 | 0xA0, 0xDB)
# TMD2771 address, 0x39(57)
# Select proximity ADC time register 0x02(02), with command register, 0xA0(160)
#		0xFF(255)	PTime - 2.72 ms
bus.write_byte_data(0x39, 0x02 | 0xA0, 0xFF)
# TMD2771 address, 0x39(57)
# Select Wait time register 0x03(03), with command register, 0xA0(160)
#		0xFF(255)	WTime - 2.72 ms
bus.write_byte_data(0x39, 0x03 | 0xA0, 0xFF)
# TMD2771 address, 0x39(57)
# Select pulse count register 0x0E(14), with command register, 0xA0(160)
#		0x04(04)	Pulse count = 4
bus.write_byte_data(0x39, 0x0E | 0xA0, 0x04)
# TMD2771 address, 0x39(57)
# Select control register 0x0F(15), with command register, 0xA0(160)
#		0x20(32)	120 mA LED strength, Proximity uses CH1 diode
#					Proximity gain 1x, ALS gain 1x
bus.write_byte_data(0x39, 0x0F | 0xA0, 0x20)
# TMD2771 address, 0x39(57)
# Read data back from 0x14(20), with command register, 0xA0(160), 6 bytes
# c0Data LSB, c0Data MSB, c1Data LSB, c1Data MSB, Proximity LSB, Proximity MSB
data = bus.read_i2c_block_data(0x39, 0x14 | 0xA0, 6)
# Convert the data
c0Data = data[1] * 256 + data[0]
c1Data = data[3] * 256 + data[2]
proximity = data[5] * 256 + data[4]
luminance = 0.0
CPL = (101.0) / 24.0
luminance1 = ((1.00 *  c0Data) - (2 * c1Data)) / CPL
luminance2 = ((0.6 * c0Data) - (1.00 * c1Data)) / CPL
if luminance1 > 0 and luminance2 > 0 :
	if luminance1 > luminance2 :
		luminance = luminance1
	else :
		luminance = luminance2
# Output data to screen
print "Ambient Light luminance : %.2f lux" %luminance
print "Proximity of the Device : %.2f" %proximity


Run this example and you should see the following , cover the sensor and alter the light on it

debian@beaglebone:/var/lib/cloud9/$ python
Ambient Light luminance : 98.85 lux
Proximity of the Device : 0.00
debian@beaglebone:/var/lib/cloud9/$ python
Ambient Light luminance : 0.24 lux
Proximity of the Device : 1023.00
debian@beaglebone:/var/lib/cloud9/$ python
Ambient Light luminance : 104.79 lux
Proximity of the Device : 6.00




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