We've compared the Google Coral Edge TPU Accelerator (CTA) and Intel Neural Compute Stick 2(NCS2), and we've addressed getting started on the CTA as well as the Intel NCS2. Each of these devices takes a different approach to the AI challenge, but one thing that they have in common is that—like any computing device—they generate heat.
To address the heat issue, the NCS2 comes equipped with prominent fins built into its housing, and the CTA features a grate pattern that appears to be designed for heat dissipation. The CTA getting started page recommends against using the maximum frequency setting unnecessarily to avoid burn injuries.
So how hot do these devices get? Do you need to wear fire-retardant gloves while handling these units? Real-world applications get quite hot, but my testing indicates that the demos are actually quite benign.
Intel Neural Compute Stick 2 Temperature Test
The first device we examined was the NCS2, which we set up and ran on Windows 10. When I began the experiment, I noticed that the hub where the NCS2 was plugged in awaiting instructions was somewhat warm. I tested it with an IR gun, and it was running at about 90°F. To avoid skewing my testing results, I switched to another hub that wasn't supplying power to my laptop. This hub tested closer to ambient conditions at 83°F.
Anecdotally, the NCS2 seems to get hotter just being plugged in, like it's using a lot of power just sitting there. I plugged it into a USB power meter, and it drew a rather modest .08-.09 amps when not in use. I ran the first "squeezenet" demo, which returned a text car identification, propelling the NCS2 to a "blistering" 87°F. I then ran the license plate demo on a customized image, which took brought the temperature up to 88°F.
Based on these readings, users don't have much to worry about in the demo mode. I also ran the demo many more times with the batch file set to loop back over and over to where it runs the license ID routines—I simply had to close out the graphics window—which eventually took it up to 104°F. This result was with a modified image that doesn't actually pick out the car, which I thought might affect the temperatures. After restoring the original and doing a more limited test, however, temperature ranges didn't reach 100°.
Google Coral Edge TPU Temperature Test
Moving on, I must report that the CTA was even more disappointing. For this test, I ran the bird ID program from the getting started example. As expected, the program identified the Ara Macao (Scarlet Macaw) image that Google provided with their demo. With this fact proved yet again, I wrote a bash script to execute this test over and over, placed it in a ceramic cup so as to not burn my house down, and went to lunch.
Roughly 30 minutes later, I returned to a CTA reading at just 86.9°F. Disappointed, the thought crossed my mind that I might not have been running the device at the maximum operating frequency. I reinstalled the Edge TPU API, ran my bash script, and let it run for another ten minutes. This time it was a little over 87 degrees. Perhaps there was a difference, but not much.
Incidentally, when plugged in and idle, the CTA pulls .01-.02 amps, significantly lower than the NCS2. As I inspected this device, it measures in at around 88°F after sitting idle for a few minutes, while the NCS2 reached 107°F.
Conclusion
While these results make for a rather anti-climactic article, it seems that neither device reaches dangerous heat levels when running their demo programs. One notable item here is that the Raspberry Pi 3 B I used with the CTA only has USB 2.0 ports, which likely hamstrings performance and therefore heat output. Perhaps a Raspberry Pi 4 would crank up the heat.
Regardless, not getting too hot is a good thing, and it certainly bodes well for actual AI use when you'll need higher performance. If you just want to try the devices out, don't let heat issues scare you off from running the demo. Interestingly, they both seem to heat up when just left sitting unattended, so you may want to unplug them when you're not using them or when you leave the office!