In some situations, the fan that cools JeVois-A33 is just too loud or consumes too much power. It is possible for JeVois to work without it. Here we show you how to convert your JeVois camera to using a heatsink instead of the fan.

During development of JeVois, we had initially planned on passive cooling with a heatsink. However, the required heatsink was so large and was getting so hot that we finally opted for a fan.

Requirements

You will need:

a working JeVois camera
a large flat screwdriver
wire cutters or scissors
super glue
a heatsink, here we used 30x30x20mm, with spike-style fins as those tend to be more efficient
heatsink (thermally conductive) glue, we got ours on ebay or aliexpress
alcohol pads
a vise with soft jaws (e.g., rubber)

Warning: The heatsink will get very hot, too hot for confortable touching. It can go up to 80C (175F).

Converting to fanless

This modification of course voids your warranty. Proceed at your own risk.
Open the case using the large flat screwdriver

Cut the fan wires. Make sure they do not get shorted!

You may want to glue the camera sensor to the case bottom using some super glue. Just beware that the invisible fumes from super glue will permanently damage your lens. So make sure that the lens is covered before applying glue to the case. In the picture below, you would slightly lift the sensor out of the case, put a very small amount of super-glue on the case in the housing of the sensor, and put the sensor back.

Examine the soldering job all around the CPU. None of the solder joints should extend higher than the CPU. Othwerwise, the heatsink could create short circuits. You may have to cover some of the solder joints with tape if you are afraid that they will come in contact with the heatsink.

Now get ready to glue the heatsink. First clean both the heatsink and the CPU and RAM chips with an alcohol swab and allow the alcohol to fully dry out. The CPU has a marking of A33 on it, and the RAM chip has Samsung.

Next, apply a small amount of heatsink glue to the CPU and to the RAM chip. Note that the RAM chip is a bit thinner than the CPU so the contact with the heatsink will not be great, but that is ok as the RAM does not get very hot anyway.

Press the heatsink onto the CPU and clamp in a vise, not too tight so that you will not break the circuit board. Allow to dry for several hours (overnight is recommended).

Ready to go, it does not look too good but let's see if it will work.

Success, in a 20C office, we get about 63C CPU temperature after 30 minutes of running TensorFlowEasy, which uses about 375% of the CPU (400% would mean loading all 4 CPU cores to the max).

That camera eventually went up to 66C after two hours.

If CPU temperature goes over 75C, the CPU frequency will automatically reduce from 1.34GHz to 1.2GHz.

You can also reduce the max CPU clock using parameter cpumax of JeVois. In the Console of JeVois inventor, type help and look for parameter cpumax which will show you a number of possible frequencies in MHz. You can then pick one of those and set it. For example,

setpar cpumax 1008

TensorFlow predict time went up from 25ms/inference to 33ms/inference, but CPU temperature dropped from 66C to 42C on our test camera.

You can also add this command to your camera's initscript.cfg file to run it each time JeVois starts.

Note: Using our BurnTest module which we use to test the cameras at the factory, we eventually reached 75C, at which point the CPU frequency automatically dropped to 1.2GHz. Temperature then oscillated between 72C and 75C while CPU frequency oscillated between 1.2GHz and 1.34GHz. BurnTest is not enabled by default because it is a terminal module (you need to reboot JeVois to kill it). If you look for BurnTest in videomappings.cfg, you will find a commented-out entry. Remove the comment character and restart JeVois to enable it. As noted, once you launch BurnTest, you will need to reboot JeVois to get out of it. While the system remained stable (no crash), we suspect that running for extended time periods near 75C will significantly shorten the lifespan of the CPU chip. This is also one of the reasons why we eventually decided to use a fan for mass production.

Conclusion

It looks ugly and is bulky and hot to the touch, but a fanless conversion is possible.

You may be able to use a smaller heatsink if you are ok with running at a lower frequency. See http://jevois.org/start/software.html and look for "fanless case" to download STL files of a case that can accommodate a heatsink with 30x20mm footprint. You can then 3D print that case. In our early tests with 30x20x6mm heatsinks, JeVois would almost immediately overheat under load. But if you can find high-efficiency and taller 30x20mm heatsinks and can work with lower CPU frequency, this could be an option. This would have to be tested, though.