Doug Conner trains with his triathlete group in an outdoor pool. His start time is 6:00 a.m., and during half of the year, its still dark out then, so he cant see the analog clock. To fix this, Doug created a waterproof timer he can place at the edge of the pool.
The nighttime swim timer uses a battery-powered microcontroller with a crystal time base that drives a four-digit, seven-segment LED. The microcontroller takes care of all aspects of timing and display, including driving the LEDs. The half-inch digits make the display easy to read from 10 feet away.
Doug Conner created a digital timer so he could check his pace on his 100-meter laps in the dark.
The timer is encased in a transparent, waterproof polycarbonate tube and can go to the bottom of the pool without leaking.
Great project. I think a piece of red plastic over the display would enhance its visibility during daylight. I had the same problem with an LED digital clock I built many years ago. The red plastic sheet over the display improved it a lot.
I have thought about replacing the mode switch with a Hall effect switch and avoiding one seal. i haven't used magnetic reed switches, but looking at some data I think they might work for the power switch. It would be an improvement if I can eliminate both switch seals completely. I'm going to look into making that change.
Adding the rechargeable batteries and inductive charger would probably add more cost and complexity than this project would merit. It also means separating the timer from the rest of my swim gear to charge it and then remembering to put it back before going to the pool.
The timer uses four o-rings to seal out the water. Two of the o-rings are visible on the white plastic end caps. The other two o-rings seal the rotary shafts that actuate the two switches. To open the case for battery replacement you need to twist and pull the cap off. The o-ring seal is pretty tight so this can be difficult. An improvement would be to add a better gripping surface on the end caps. Currently I put the plastic end cap in a vice and twist the clear polycarbonate body. As you can probably imagine, i've had the cap off many times during development. It doesn't compromise the seal.
One hundred hours on 4 AA batteries. Not bad for an active LED display. This could be turned into a manufactured product with a couple of minor changes so the case's integrity would never have to be breached.
1) Replace the through shaft switches with magnetic proximity detection, either Hall effect devices or reed switches with magnetic actuator buttons or a magnet on a lanyard on the outside of the case.
2) Replace the alkaline primary cell batteries with rechargeable cells, charging circuit and induction coil.
Place the unit in a magentically coupled charging station between uses.
One gotya with secondary cells is to be sure there is a safety vent mechanism in the waterproof case to prevent pressure buildup should the batteries outgas.
The website at the end of the video shows how he made it waterproof.
Excerpt from that page:
To use this timer I needed two switches accessible from the outside. I also needed to see the LED display yet protect it from water. That led me to a design where the entire system is housed in a waterproof case made from a polycarbonate tube with acetal (a type of plastic) end caps. The two end caps are sealed with the polycarbonate tube by using two O-rings (the black rings in the photos). Only the switches need to penetrate the end caps.
While many of Design News' Gadget Freak projects are cool and useful to the person creating them, this is one that really could be mass produced and put on the market. Doug, how did you seal the case to make it waterproof? Also, once the batteries run out, is there a way to replace them without compromising the waterproof nature of the clock?
Forget about Doug's innovative work creating a digital timer leveraging LED displays. How about the fact that Doug and crew are up swimming in an outdoor pool well before the light of day. I'm shivering and cold just thinking about it. So frankly, I have to applaud that effort, Doug, and I admit, your gadget is pretty nifty!
If you have a Gadget Freak project, we have a reader who wants to make it. And not only will you get your 15 minutes of fame on our website and social media channels, you will also receive $500 and be automatically entered into the 2015 Gadget Freak of the Year contest.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.