What is it?

This is Excelitas' TPiS 1S 1385 CaliPile™ thermopile IR temperature sensor on a small (0.7 x 0.4 in) breadboard-compatible breakout board.

From the datasheet: "The TPiS1S1385 is the most compact thermopile sensor with integrated signal processing within the CaliPile™ product range. It features a wide field of view and a low power consumption. The technology of a high sensitive thermopile combined with a smart data treatment allows for much more than the traditional temperature measurement of remote objects. Once configured via the I2C interface an interrupt output can be used to monitor motion, presence or an over-temperature of remote objects."

The CaliPile™ connects to your microcontroller using fast (400 kHz) I2C; there are 4K7 pullups on SDA and SCL already on the board. The CaliPile™ maximum input voltage is 3V3 so use a logic level translator for 5 V systems. There is a multifunction interrupt (pulled up by a 10 K resistor, active LOW) available for alerting the microcontroller host when the temperature crosses a threshold, when presence or motion is detected, or when a thermal shock condition is detected or all of the above. An interrupt status register can tell the host which is the cause of each interrupt and take appropriate action.

The board also exposes the two address pins (pulled LOW by 10 K resistors), so that four of these CaliPile™ breakout boards can be used on the same I2C bus. Even though the CaliPile™ has a wide 120 degree field of view, combining two or more can allow presence detection over a full room volume.

The CaliPile™ works by detecting IR radiation from 5.5 microns (filter cutoff) up to 13.5 microns. The CaliPile™ holds calibration and conversion data in the on-sensor EEPROM that has to be read and then applied to convert raw counts into ambient temperature and object temperature. The range of linear temperature detection is -20 to 85 C, but a wider range of object temperatures can be detected with proper calibration and depending on the ambient temperature. Consult the data sheet for more information.

The CaliPile™ is an ultra-low-noise thermopile. Typical noise level on the CaliPile™ is +/- 5 counts with a typical sensitivity of 400 counts/degree Kelvin. The CaliPile™ is also an ultra-low-power sensor, requiring a maximum of 15 uA for normal continuous operation. Yes, that's right, 15 micro amps!

If the CaliPile™ were just a high-resolution, ultra-low-power thermometer it would be useful enough. But the CaliPile™ has an embedded smart ASIC that can be configured to detect human presence, human motion, thermal threshold crossing, thermal shock conditions, and timing conditions. In other words, this small thermopile can tell if someone has entered a room, if they are moving inside it, if they have stopped moving but still present, and if they have left.

In fact, the configurability of the CaliPile™ means it can do even more than this once tuned for your particular use case. The parameters that determine temperature threshold, presence and motion detection are completely configurable by the user and custom settings can be chosen to define an almost endless set of interrupt conditions to match your use cases.

Why did you make it?

Temperature threshold detection might seem like a simple problem, but detecting human presence and motion in a space is not easy, especially if you have to worry about power consumption. When average power usage is critical, like for any remote, battery-powered, connected application, then low power sensors become critical too.

I wanted a way to detect human and animal presence and motion using a device that could be deployed for months or years, using an ultra-low-power host (like this one) that could remain asleep for most of the time until alerted by the sentinel sensor that something interesting had been detected. In this case, the host will wake up, interpret the data (coming, going, present, moving, etc), enable a radio modem, report the state changes to a server, turn off the radio modem, and then go back to sleep.

Such a system cannot last long if the sensor, which has to be ready at a milliseconds' notice to alert the host MCU, uses a lot of power to do its job. Consider, one month has ~720 hours. If such a sentinel sensor were to use several mA in continuous mode, even a fairly large (2000 mAH) battery would last only a month or two. However, at 15 uA, plus another 100 uA or less for the host and radio modem (remember, these are off >95% of the time), such a system could last a year or more. Or at least this is the promise of the CaliPile™ thermopile.

I have just started to use this interesting little sensor and have yet to field even in prototype such a sentinel system, but I am working on it. The CaliPile™ makes such a project feasible!

What makes it special?

This is a small breakout board that exposes all of the sensor IOs for easy breadboard use, and its small size allows it also to be incorporated directly into almost any project.

I have written a complete Arduino sketch to configure the sensor, read the ambient and object temperatures, set up the interrupts, and output all of the interesting data including presence and motion detection interrupts on the Arduino IDE serial monitor.

I have also used the Arduino IDE serial plotter to plot the data and follow the very useful tutorial Excelitas prepared for their Evaluation kit, which is not required to get full advantage of the tutorial. Simply connect this CaliPile™ breakout board to your favorite MCU and use the serial plotter to follow along the experiments described by Excelitas' CaliPile™ Application Software Evaluation Guide.

Order the pcb from OSH Park and assemble some of your own or buy the fully assembled and tested CaliPile™ breakout board from me and see how easy it is to add presence and motion detection to your project!