Intro: Simple LED Circuit on the Cheap
I needed to make 15 simple circuits with a light, battery and switch that could be easily assembled and disassembled multiple times for a Cub Scout camp activity. The light need to be bright enough to be visible in direct sunlight (working outside). And they needed to be as cheap as possible.
The prices, parts and sources were the cheapest I found for ordering enough for 16. I ordered 1 extra because it was cheaper then needing to order a replacement later if a piece was lost or failed due to shipping costs. The batteries are the only thing that didn’t come as individuals, but ordering significantly more or less of these may result in another source being cheaper.
16x RL5-BR2020: Super Bright (4000 mcd) 5mm Blinking Red LED - $ 0.54 ea - $11.85
16x SPST10: SPST on-off Miniature Toggle Switch - $0.60 ea - $13.60
2x Lithium 3V Batteries Size CR2032 (Pack of 25) - $3.95 ea - $7.41
10ft Solid copper 18 gauge door bell wire (two wires) - $0.23 ft - $2.53
Electrical tape (on hand)
Solder (on hand)
Hot glue (on hand)
Scrap wood (on hand)
Total price: $35.39 (with shipping, tax, etc.) or $2.35 each (with one set of spare parts)
Some of the pictures are upside down. They appear the correct orientation on my Mac as it reads the orientation information from the camera but provides no convenient way to rotate images like Windows 7. Sorry about that.
And here is one circuit blinking:
Step 1: The Boards
The wood I used was 3/4 inch thick. I had some that was only 1/2, but it was a little thin, so I recommend the 3/4 inch. I cut it into squares with 3 to 4 inches per side. The thickness of the wood is dependent on the size of the switch.
The more C clamps you have the more boards you can work on at the same time.
Each board has a large hole for the switch. This hole is made with two different bits. First drill a 1/4" hole clear through, then a 5/8" hole most of the way through. Use masking tape on the drill bit so you know when to stop. Leave just enough wood to hold the switch in place when you tighten the nut.
I then drilled 6 small holes in the wood. The holes right next to the switch mounting are used to run wires from the poles of the switches on the underside to the top of the board. The other two sets of holes are for the battery and LED respectively. You want the holes for the switch quite close to the 5/8" hole. The other two holes should be about an inch appart. You might make a battery assembly first and examine the leads on your LEDs first to see what is the idea distance for those holes.
Experiment with bit sizes to find one that works for the size of wire you are using. The holes should be just barely larger than the wire that goes through them. The idea is that by poking two wires in the same hole it should be tight enough to maintain contact between the two. I forget what size bit I ended up using. I think it was the smallest I had.
Step 2: Mounting the Switch
Mounting the switch was the main purpose for the boards. Without the switch being properly mounted it is a pain to turn it off an on.
With the 3/4" board it was thick enough to completely recess the switch, so I carved notches to allow the wires to run from the switch poles to the holes. This is the ideal, but I also used some 1/2" wood.
The switch comes with 2 nuts and 2 washers. One of the washers has a key to keep the switch from turning, and the other has teeth. I placed the teethy washer on the bottom and the keyed washer and one nut on top. I didn't use the extra nut.
To run the wire from the poles to the top of the board it is important to measure it to be long enough to make it from the pole, through the board and then have enough left to hook it on the poll and fold it over on top. Just want a bit of wire on the top. It might take a couple attempts to get the right length. Strip the wire completely.
After the wire is hooked on the poles and ran through the board apply a small bit of solder to attach the wire to the poles of the switch. If you don't then the glue may result in the wire not making contact. Then put hot melt glue on the contacts and around the switch. This prevents short circuits and keeps the switch from moving. Also put a drop of switch on the nut on top to it doesn't come loose.
Step 3: Creating the Batteries
I constructed a 6v battery from two of the 3v button cells. The LED will light with a single cell, but it is much brighter (and lasts longer) with two. The suggested voltage is 5v with a min of 3v and a max of 10v, so 6v is near optimum. I could have used 3 cells for a 9v battery I suppose. Maybe next time.
To create the leads I used two pieces of wire. I wrapped one stripped end of the wire with some aluminum foil to increase the surface area of the connector, and to make it larger than the insulator. In my tests this seemed to make it significantly more reliable.
Place a strip of tape sticky side up, then put down one lead, two cells and the other lead. I liked to attach the red wire to the positive side of the cells. Then wrap the tape around it. Finally wrap another strip of tape perpendicular to the first.
Strip the other end of the leads too.
Place the battery on the board with the two leads in two holes. Place the LED on the board with its two leads in two holes as well. Ideally the positive LED lead should be on the same side as the positive battery lead.
Step 4: Final Assembly
Two small drop of glue attach the LED. The glue should be near te middle of the LED and not near the holes. Some glue under the battery (again not near the holes) will keep it in place too.
Each circuit needs 3 pieces of wire with both ends stripped: Two long and one short. The exact length depends on the sizes of your boards and the placement of the components. I made mine long enough to allow for hooking the circuits up without the switch, and backwards so they can see what happens then (nothing).
Here is attaching the wires and using the switch:
and just the blinking LED. I tested it outside in bright sunlight and it is still visible.
Hopefully that will be interesting and simple enough for the scouts.