EyeTribe Hacks - 1 Power

[Memo]

The Story: I had to start my new hardware project in the last weekend but some of my spare parts order was delayed. So, I decided to start this hacking series just for fun while waiting my parts. Because of this report have quick assumptions, if you have a plan to make a hardware or software project for the EyeTribe, please do your own research. Even better ask EyeTribe People..

OK let's check EyeTribe USB properties for to learn how much power requirements reported. EyeTribe exposing itself as a USB Composite Device plus a USB Video Device. According to the below reports, device total 5V DC power current requirement is 896mA. Just below of 900mA (4.5W) which is USB 3.0 maximum DC current supply level.

First Result: If you want to connect EyeTribe to your computer via a USB 3.0 Hub, you definitely need an external powered hub. Since 4mA is not enough to drive a USB powered HUB. (Consider at least the hub itself needs around 100mA)





Now, it's time to check the real power consumption. To make this we need to throw away a working USB 3.0 cable by cutting it in the middle.

The cable length was 1.8m and probably will not be working after the cutting (decreasing the signal quality). I make it shorter to total around 40cm.

OK I void 10$ for you guys.



Now it's time to connect these cables back according to their colors except the RED line. RED line is power line and we will put in our multimeter at DC current measurement position.


When I connect the EyeTribe device, it consumes 240mA without running EyeTribe Server.

Second Result: EyeTribe consumes 1.2W in Standby position (An ordinary portable MP3 player consumption). The internal circuit is active.


When I run the EyeTribe Server the consumption rises to 442mA while in internal testing. Since IR LED groups are illuminated serially.


After the boot up test finished, it's drawing total 284mA. The difference is 44mA and probably the camera becomes activated.

Let's see what will happen if we run EyeTribe UI...


Uncalibrated = 760mA


Calibrated = 779mA (3.895W)

Max power (779mA) - Nominal power (284mA) / Total IR LED (12) = 41,25mA per Infrared LED current consumption.

Reported power requirements (896mA) - Max power consumption (779mA) = 117mA

Last Result: %15 less max power consumption shows that EyeTribe plays in the safe zone. Good design, congratulations.

Note: You may thing you can use a USB powered hub since 117mA less consumption. My advice is not. The EyeTribe may work erratic since figures can be change according to environment changes like temperature or humidity (consider momentary current spike over loads also)... Use external powered USB hub if you needed and stay in the safe zone.

Next: EyeTribe Hacks 2 - Temperature

[stefan.eickelberg]

Very interesting, thanks. I am actually looking for an extension cord for the tracker right now. So you're saying anything but a USB 3.0 Hub with external power source won't do the job? I need something around 5 m, so I am currently thinking: 3m usb cable to externally powered hub to the 2 m cable shipped with the tracker.

[Memo]

That was an interesting read, thanks. However, I do question the information a little, since the cable that comes with the tracker is already 2 meters long whereas the maximum length of such cables is suposedly 1 m, according to that article.

I just checked some industry camera suppliers. They all offer USB 3.0 Micro B cables up to 5 m. They HAVE to work, if they offer them there, but they might as well be some special cables, because they cost like 60 €. More than half of what the eye tracker costs.

Very interesting, thanks. I am actually looking for an extension cord for the tracker right now. So you're saying anything but a USB 3.0 Hub with external power source won't do the job? I need something around 5 m, so I am currently thinking: 3m usb cable to externally powered hub to the 2 m cable shipped with the tracker.

OK, let's start with clearing something about the cable distance. Producers and standardization organizations always recommends values in the safest limit (not safe but the safest). This doesn't mean that you can't break this limit but you must be ready for the cost. The cost is sometimes become speed, sometimes safety, sometimes erratic working, sometimes a possibility of a fire or sometimes not a significant overload... just you name it. But there is always a cost to exit their recommended limits. If we have enough knowledge about the subject, breaking the limits might be quite acceptable. Am I breaking the limits? Definitely yes, after make my calculations and researches like you. So, 1m is a recommended limit to keep you in the very safe zone.

As you seen my above article the cable length was 1.8m and it was working fine with EyeTribe. When I cut in the middle of it, only 6cm becomes unshielded. It didn't work as I expected since the signal quality changed. I made the cable length shortened to 40cm to recover this loss.

Every case needs different considerations. Our case is transferring digital video signal to the computer via USB 3.0 standard. The primary role belongs to the speed and amount of the data. EyeTribe has 30 and 60 frames rate per second. We may not notice if a couple of frames dropped out but when the cable length becomes overlong too much, data loss rate increases. Eventually it reaches a level of high error rate. EyeTribe Server cannot recover and produce a meaningful data. Until the time of EyeTribe Server refusing to working, you will be not aware of you are working at the edge of dropping point. (Sometimes erratic working gives us a clue...)

In your case, you need at least a 5m extension usb cable. I can't say that you can't find cheap and high quality cable but according to my humble opinion, you really need to kiss a lot of frogs until to find the prince of the cable . Please share with us here in this forum if you succeeded.

On the other hand, using at least a one active usb 3.0 hub (externally powered) as you mentioned comes to me best logical solution and I think it has a great chance to work. By the way not all usb 3.0 hubs are the same. Some of low quality hubs may not work right and if I remember correct EyeTribe has problems with some kind of usb bridge chips.

I wish you a good luck and like to hear your success in this article.