TPA81 - 8x1 Thermopile array

Detects a candle flame at a range 2 metres (6ft) and is unaffected by ambient light!
Detect Human Body heat!
Servo control for image construction!


8 Pixel Thermal Array Sensor

Voltage - 5v only required
Current - 5mA Typ. excluding servo
Temperature Range - 4°C - 100°C
Accuracy (Full FOV) - +/-2°C +/-2% from 10°C to 100°C,
Accuracy (Full FOV) - +/-3°C from 4°C to 10°C
Field of View - 41° x 6° (8 pixels of approx. 5° x 6°)
Outputs - 1 ambient + 8 pixel temperatures
Communication - I2C Interface
Servo - Controls servo in 32 steps to 180° rotation
Small Size - 31mm x 18mm

Technical Specification

Introduction
The TPA81 is a thermopile array detecting infra-red in the 2um-22um range. This is the wavelength of radiant heat. The Pyro-electric sensors that are used commonly in burglar alarms and to switch on outside lights, detect infra-red in the same waveband. These Pyro-electric sensors can only detect a change in heat levels though - hence they are movement detectors. Although useful in robotics, their applications are limited as they are unable to detect and measure the temperature of a static heat source. Another type of sensor is the thermopile array. These are used in non-contact infra-red thermometers. They have a very wide detection angle or field of view (FOV) of around 100?and need either shrouding or a lens or commonly both to get a more useful FOV of around 12? Some have a built in lens. More recently sensors with an array of thermopiles, built in electronics and a silicon lens have become available. This is the type used in the TPA81. It has a array of eight thermopiles arranged in a row. The TPA81 can measure the temperature of 8 adjacent points simultaneously. The TPA81 can also control a servo to pan the module and build up a thermal image. The TPA81 can detect a candle flame at a range 2 metres (6ft) and is unaffected by ambient light!

Spectral Response
The response of the TPA81 is typically as shown below:

Field of View (FOV)
The typical field of view of the TPA81 is 41?by 6?making each of the eight pixels 5.12?by 6? The array of eight pixels is orientated along the length of the PCB - that's from top to bottom in the diagram below. Pixel number one is nearest the tab on the sensor - or at the bottom in the diagram below.

Sensitivity
Here's some numbers from one of our test modules:
For a candle, the numbers for each of the eight pixels at a range of 1 meter in a cool room at 12 deg.  are:
11 10 11 12 12 29 15 13 (All deg.)
You can see the candle showing up as the 29 deg. reading. At a range of 2 meters this reduces to 20 deg. - still around 8 deg. above ambient and easily detectable. At 0.6 meter (2ft) its around 64 deg.. At 0.3 meter (1ft) its 100 deg.+.

In a warmer room at 18 deg., the candle measures 27 deg. at 2 meters. This is because the candle only occupies a small part of the sensors field of view and the candles point heat source is
added to the back ground ambient - not swamped by it. A human at 2 meters will show up as around 29 deg.  with a background 20 deg. ambient.

The following is a snapshot of our test program. It displays a 32x8 bitmap produced by using a servo to pan the sensor. If you want a copy of this windows based program, its here, but you will need an RF04/CM02 to connect the TPA81 to your PC. Here you can see a candle flame about a meter away showing up as the bright spot.

Connections
All communication with the TPA81 is via the I2C bus. The TPA81 uses our standard I2C 5 pin connection layout. The "Do Not Connect" pin should be left unconnected. It is actually the CPU MCLR line and is used once only in our workshop to program the PIC16F88 on-board after assembly, and has an internal pull-up resistor. The SCL and SDA lines should each have a pull-up resistor to +5v somewhere on the I2C bus. You only need one pair of resistors, not a pair for every module. They are normally located with the bus master rather than the slaves. The TPA81 is always a slave - never a bus master. If you need them, I recommend 1.8k resistors. Some modules such as the OOPic already have pull-up resistors and you do not need to add any more. A servo port will connect directly to a standard RC servo and is powered from the modules 5v supply. We use an HS311. Commands can be sent to the TPA81 to position the servo, the servo pulses are generated by the TPA81 module. 

Registers
 The TPA81 appears as a set of 10 registers.

Only registers 0, and 1 can be written to. Register 0 is the command register and is used to set the servo position and also when changing the TPA81's I2C address. It cannot be read. Reading from register 0 returns the TPA81 software revision. Writing to register 1 sets the servo range - see below. It cannot be read back, reading register 1 reads the ambient temperature.

There are 9 temperature readings available, all in degrees centigrade. Register 1 is the ambient temperature as measured within the sensor. Registers 2-9 are the 8 pixel temperatures. Temperature acquisition is continuously performed and the readings will be correct approx 40mS after the sensor points to a new position.

Servo Position
Commands 0 to 30 set the servo position. There are 31 steps (0-30) which typically represent 180 deg. rotation on a Hitec HS311 servo. The calculation is SERVO_POS*60+540uS. So the range of the servo pulse is 0.54mS to 2.34mS in 60uS steps. Writing any other value to the command register will stop the servo pulses. 

Mechanical Layout

Customer Reviews: