We usually experience temperature as a more or less nebulous quantity that characterizes an oven, or a room, or an entire geographical region. But we need to remember that a typical thermometer is not the only way to interact with temperature; we can also go directly to the heat emitted as infrared radiation.
A warm object will radiate more infrared radiation than its room-temperature surroundings. If we use an electronic device that is sensitive to infrared radiation, we can detect this object. If we combine numerous such devices into an array, we now have the equivalent of an image sensor. The result will be multiple pixels of infrared intensity data, and this data can be interpreted as thermal imagery.
Here you see the grid-EYE board connected to a larger board via the mikroBUS interface.
Let’s take a look at the sensor itself.
First of all, it’s important to understand that this thermal array cannot be compared with your typical image sensor in terms of resolution. Digital cameras these days offer over 10 million pixels; the AMG8853 has 64. It’s a thermal image sensor, yes, but we’re talking about an 8-pixel-by-8-pixel image—not photograph quality, but adequate for crude image processing, and certainly better than a single detector that gives you no details about the nature of the warm object in front of the sensor.
Diagram taken from the datasheet.
As usual, the AMG8853 is highly integrated: all the analog processing is handled on-chip, and the temperature information from the sensor array is provided as digital data via I2C.
High-performance thermal sensor applications may employ infrared-sensitive diodes, such as InSb (indium antimonide) or InAs (indium arsenide) diodes. And if you really need to maximize performance, you might even enclose your diodes in a very-low-temperature environment. The AMG8853, on the other hand, uses thermopiles; in a thermopile array the individual detectors are thermocouples, which means that they convert temperature differences directly to voltage.
It’s important to remember that the AMG8853 is measuring temperature via infrared radiation, not via conduction or convection. This means that your data will be inaccurate if something (such as moisture or glass) is preventing infrared radiation from reaching the sensor.
I readily admit that I don’t have significant experience with these types of sensors. Nonetheless, my general impression is that this is not a fabulous way to measure temperature. If all you need is a rough measurement I’m sure it’s fine, but my guess is that the AMG8853 is more interesting as a detector or crude thermal imager. The 64-pixel resolution probably won’t allow you to determine, for example, which types of nocturnal critters are depredating your garden, but it might tell you if they’re big or small, or how they get over the fence.
As usual, the AMG8853 comes in a difficult-to-solder package (surface mount, leadless). If you don’t feel like breaking out your toaster-oven reflow equipment, you can buy the grid-EYE click evaluation board from MikroElektronika (they’re still on preorder; shipping begins April 18th).
The grid-EYE click is essentially a breakout board for the AMG8853, so don’t expect a lot of amazing functionality in addition to what the sensor itself does. The schematic shows the sensor, pull-up resistors, two voltage-level translators, and typical support components.
The schematic for the grid-EYE board. Click here to enlarge.
The AMG8853 is a 5 V device, but the voltage-level translators allow it to communicate via 3.3 V or 5 V logic. Both the I2C address and the logic voltage can be selected via zero-ohm resistor. (I find this annoying, as I don’t like soldering surface-mount components; I would much prefer 0.1-inch shunt jumpers.) Also, it seems to me that the label “VCC SEL” is not quite accurate: the AMG8853 always operates at VCC = 5 V; the zero-ohm resistor simply selects the interface voltage.
Like other click boards, the grid-EYE is compatible with solderless breadboards and the standardized mikroBUS interface.
The idea behind this interface is that any mikroBUS-compatible board can be connected to a mikroBUS socket. This provides flexibility in terms of hardware functionality—one interface, many boards. There is also firmware support; click here for the grid-EYE sample code.
Do you have any experience with the click development boards? If so, let us know what you think.