DIY High-Speed Book Scanner from Trash and Cheap Cameras

Step 58: Handle/Electronics: Hub

Locate your USB hub. I found this one in the trash bin at work -- it was some kind of medication promo. Since USB1 is outdated, you should be able to easily find this kind of hub for free. Recycling it gives it new life.*

Comments

[autophile]

Well, it's possible that the caps don't hurt. I also found that 3 volts didn't trigger my particular camera, and that I had to use 4.5 volts. In diagnosing the voltage problem, I figured that the fewer complications to troubleshooting the better, so in the end I was left with just the bare USB connectors. So for everyone trying this at home: if at first it doesn't work, try increasing the voltage to 4.5 volts first. If that doesn't work, then you can strip your hub to the bare essentials!

[autophile]

You probably don't want to use any hub that can be powered by AC if you can avoid it. Check with a continuity meter to see if there is a direct connection between the rightmost pin (or pin 1) of the outputs and the rightmost pin (or pin 1) of the input, and also between the leftmost pin (or pin 4) of the outputs and the leftmost pin (or pin 4) of the input. If not, you will have to wire the pins together. Even then, you are not guaranteed that it will work. Your hub may have large electrolytic capacitors (blue or black cylindrical things) between pin 1 and pin 4. These are supposed to help the hub maintain power. Of course, you don't want to do that -- you want to be able to apply power and then remove power instantly. The capacitors will let you apply power, but when you remove power, the voltage will only drop slowly as the capacitors leak their lifeblood (i.e. electrons) into the circuitry. In the end, I decided to sidestep all the problems and just cut the circuit board around the USB jacks and wire them up (pin 1 to pin 1, pin 4 to pin 4).

[daniel_reetz]

Great instructions. Well done. In my case, there isn't a connection between the input and output (but of course the grounds are connected), and believe it or not, the caps and junk in the USB hub seem to help debounce my button presses. In revision one of my trigger circuit, I would occasionally have the problem that one camera would trigger focus but not fire. Using the hub wholesale (and a current version of SDM) killed this problem. Still, your description is the superior solution. I used the whole hub primarily to make things "simple".