I built a cable using a USB cable, Altoids gum box (mini), 9V battery, and LM7805 5V regular. On an SD850, the 3V button cell was giving me erratic results, and I needed 3.5-5V to trigger. I actually got really good results with a 7.4V battery (by accident), but I wasn't daring enough to keep using it.
I do have a problem where sometimes when I press my USB remote, I get a half_shoot shutter condition, instead of a full shoot. The meter box shows up on my screen, but I can't get it to take the shot. Sometimes it works fine. I can't tell if the problem is my USB cable which has extremely small wires. It is the retractable type which doesn't work well for high speed transfer, which is why I sacrificed it.
Anyone else see this problem?