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This article was originally posted on Instructables and is reposted with permission from Michael Chen.
Bicycle turn signals really improve the visibility of cyclists at night, and yet you rarely see anyone wearing them. We designed this do-it-yourself project so cyclists could easily be seen by drivers while riding the streets at night. Check out the awesome EL panel that will flash like lightning when you signal your turn.
The operation of these bicycle turn signals is entirely hands-free. They operate automatically when you extend your arm. Even raising your arm slightly causes the mercury tilt switch to complete the circuit and lights up the EL panel. Give this DIY project a try, and you'll be amazed at how it will increase your nighttime bicycle safety.
Step 1: Assemble the Materials
2 EL panels — Dual arrows, with AA-battery-powered AC inverters (the EL panels and the inverters may be separate; if you'd like to have solid EL panels, soldering might be required)
2 mercury tilt switches
4 to 6 pairs of adhesive-backed Velcro fastener strips
2 1.5-volt alkaline button cell batteries — AG13/LR44
Step 2: Place the Button Cells
Cut a tiny piece of electrical tape to about the width of the batteries. Loop the tape so its sticky side faces outward, then adhere it to the side of one of the button cell batteries (see photo at left). Place the battery inside the inverter battery compartment, with the negative side — the side without writing — touching the spring inside the compartment (see photo below, right). Repeat these steps with the second inverter's battery compartment.
Step 3: Insert the Mercury Tilt Switch
Be very cautious during this step because the tilt switch contains mercury, which is very toxic.
Place the mercury tilt switch inside the inverter battery compartment (see the photo at right). Manipulate the mercury tilt switch so that its two wires are on opposite sides. Make sure to bend the leads slowly and flex them accordingly. You don't want to make this more difficult for yourself by breaking a lead or the mercury bulb.
Make sure that one wire touches the positive side of the inverter battery compartment and the other wire touches the button cell (again, see photo at right). If you wish to make the switch's position more secure, you can solder one of the ends to the positive side where an AA battery is supposed to go. This will ensure that the switch does not slip out while you're cycling. Slide on the plastic lid for the battery compartment. Repeat this step with the remaining inverter's battery compartment.
(Be sure to point the switch's mercury-filled bulb toward the positive side of the battery compartment when you're installing it.)
Step 4: Test
Plug the inverter battery compartment into the EL panel plug. Raise the battery compartment to about 15 degrees so that the mercury completes the circuit. If you're successful, the EL panel will light up. If the panel doesn't light up, remove the inverter battery compartment's lid and manipulate the tilt switch a bit until it works. Be careful not to break the mercury tilt switch. Repeat this step for the other completed EL panel. There should be two options for the light — blinking and steady. Make sure to switch this on to test it, tilting the battery compartment up and down. The connections from the pack to the EL panel are fragile. Try not to bend them or you may have to solder them back in place.
Step 5: Make the Armbands
We recycled old shirt sleeves to make the armbands because LED armbands are too expensive. We cut the bands wide enough that there was still about a half-inch clearance on both sides (top and bottom) of the Velcro. You don't have to know how to sew well to complete this step. There are many methods of sewing; we just stitched down the corners. Make sure you match up the Velcro strips — hook (spiky) to loop (fuzzy). If you sew two hook Velcro bands on the same side of the armband, you'll have to tear out the stitches on one and start again. Put one Velcro patch on the end of the armband (it doesn't matter which side) and the other on the back of the opposite side. When you loop it around your arm, the two pieces of Velcro should stick together to make an armband. Repeat this step to make the remaining armband.
Step 6: Place the Velcro for the EL and Battery
Cut two hook and loop pairs of Velcro fastener and stick them onto the backs of the two EL panels and inverter battery compartments (see photo at left).
Next, you'll have to sew Velcro patches onto the armband that correspond with the inverter battery pack and the EL panel. Remember that fuzzy (loop) goes to spiky (hook) for the Velcro. Check out the photo at bottom left — you can see the stitching from the back of another piece of Velcro. Here's a tip to help you with placement of the EL and battery Velcro strips: Make sure you stitch a patch behind the Velcro strap that overlaps the other strap for the armband closure. Then just stitch the other patch in the middle on the same side. It doesn't matter which patch goes where on the armband, so long as they look like this (see photo below, left). Stitching through the two layers of Velcro will take some muscle to puncture and pierce with a sewing needle, so do this with caution.
Step 7: Strap on the Armbands
Wrap the band on your arm and adjust it to be comfortable. Make sure the Velcro corresponding to the EL panel is on the back part of your arm, and the battery pack is in (or near) the front. Just stick the EL panel onto the Velcro and angle it however you want. Make sure to point the arrows toward the ground so they'll indicate the correct direction when you lift your arms to signal a turn. The same goes for the battery pack. When you attach the battery pack, make sure the wiring goes up your arm and toward your body. This will cause it to trigger when you lift your arm but not when you drop your arm. Angle it according to how high you want to lift your arm when signaling. Attach the EL panel first, and bring the wire toward your body and place it on the Velcro; this will ensure that the wire won't fly everywhere or get caught on something.
Now you're ready to roll with your DIY bicycle turn signals. They're a great bicycle accessory. Be safe out there!
When removing the armband turn signals, be sure to first remove the pack or panel before you unstrap the entire band.
Step 8: Troubleshooting
Flickering and loose connection: Try a little piece of tape to secure the ends of the switch to the battery.
Light not turning on: Make sure the ends are touching either the battery and positive plate and mercury is touching ends. The battery might be dead, or there may be a disconnected wire.
Disconnected EL panel and wire: Solder it back together, and be careful not to melt anything.
For more photos, see my original post on Instructables.