Stephen

Almost without fail, there has always been some small unforeseen issue with each successive build, but thankfully they've all been manageable. Although I really thought I was going to escape the trend with build #4, Murphy says, "Not so fast..."

The problem is with the new power switch scheme. With build #4 I got away from epoxying the switch into the lid and now have the power switch integrated into the PC board. From a manufacturing standpoint, this is great, but how do you depress the switch? This is where the newly designed silicon seal and button cover comes into play. From the image below, you can see the very simple design approach. The assembly stack goes like this...



1) PC-board with mounted switch inside main housing
2) Silicon button cover (sits in precision routed slot)
3) Aluminum cover and four screws compresses the silicon seal and makes the housing water tight.

And for the majority of the time this assembly works just great. However, there are some conditions that could impact it's operation, but first, lets talk about power brake boosters...

Huh? What does a car's power brake booster have to do with bike lighting? We'll in this case, under certain circumstances, the DS power switch stackup can act just like a brake booster. In the power booster scenario, the car's engine generates a vacuum and applies this to the chamber of the booster. A large diaphragm is then pulled down by the vacuum, thereby adding force to the brake cylinder piston. Now if we transfer this same idea to the DS housing, we now have an enclosure containing a large (relative to the power button) diaphragm. All we need now is a vacuum to make the analogy complete.

So if you remember back to chemistry class days... when you take a constant (sealed) volume of air at room temperature and cool it down significantly, there is an equality that must be satisfied. If the temperature goes down and the volume cannot change, then the pressure inside the enclosure must go down to satisfy the equation. If the pressure goes down enough, the diaphragm (silicon switch cover) can actually be pulled down hard enough to depress the power button!

OK, so how does this effect you? Well, unless you ride in temperatures below around 30F, then you can stop reading right now. It's very likely that the problem won't show up until temperatures are in the mid 20s (Fahrenheit). Even then, testing that I've been performing has shown that the problem may only be present on about 35% of the build #4 units that have been sold so far (around 120 pieces). So if you've ridden in these kinds of temperatures with no issues, then you're good to go. But what if you're one of the "lucky" ones that has the perfect combination of conditions for this to happen? Never fear... there is a simple fix, and it involves a small piece of heat shrink tubing that I will be making available to anyone who needs it.

In the meanwhile, if you find yourself out on the road with this problem, the immediate solution is to take your 5/64" (2mm) Allan wrench and loosen the four cap screws in the lid until the seal is broken. When you do this, you will have restored normal switch operation, until potentially the next time you find yourself in the same conditions. The permanent solution is to add a small piece of flexible heat shrink tubing to the "pusher" on the underside of the silicon button cover. In essence this piece will act as an extra spring force, thereby preventing the diaphragm from being "sucked" down and depressing the switch. The end result is a slightly stiffer power button, but testing has shown that it does indeed solve the problem. I'll be posting more pictures and an instructional video later.

NOTE: In the event that you find yourself out in the cold with a "stuck down" power button, be sure NOT to disconnect and then reconnect the battery in this situation since it will put the light into programming mode.

Shown below:
1) The jig I had to make for dialing in the necessary length of the tubing and cutting repeatably.
2) The switch cover gasket with and without the fix.