Build a working flashlight using a 3D printed case, electronic components, and a soldering iron. The case has a belt clip and a hole for a lanyard or key ring. All the parts may be purchased through eBay in quantities that make this an inexpensive project for your group - make717 builds these at community maker faires for less than $1.50 each.

Step 1: Theory, Don't Skip It!

An LED gives off light when electricity passes through it. It can run at almost any voltage as long as the current stays within the design limits of the LED. Our circuit uses a 9 volt battery. To keep it from burning out the LED, we use a resistor to limit the electrical current. A switch turns the LED on and off.

The schematic shows how the parts relate. We will construct this circuit using "dead bug" techniques, so there is no need for a printed circuit board.

The math (from http://www.electroschematics.com):
(Source Voltage – LED Voltage Drop) / Amps = OHMs 

Amps = mA/1000

If your LED has different ratings, you can use this formula to adjust the value of the resistor.

The wrong resistor could cause your LED to burn out!

Example: 

Source Voltage = 9 volts .

Voltage Drop = 3.1 volts typical for a blue or white LED

 Desired Current = 13 milliamps

(9 – 3.1) / ( 13 / 1000 ) = 452 ohms; 470 ohms would be the nearest standard value.

Our LED specs:

Water Clear White 5mm

3.0-3.2V Voltage Drop

20mA Desired Current

Using the math from above, (9-3.0) / (20/1000) = 300 ohms would be an appropriate resistor.

Step 2: 3D Print the Flashlight Case

An STL file for FlashLight Gen 4 is provided. Print this STL file in PLA. It takes about an hour with a typical printer. You may finish the rest of the project while the model prints. The flashlight is designed to be printed with the flat top down (belt clip up) as shown.

TIP: if you are doing a group project, print multiple copies at once. At make717, we print 9 flashlights at a time. Print a pile of them in advance, and let your group replenish the supply while they complete their projects. This reduces assembly time to about ten minutes.

PRO TIP: The flat side is a great place to laser engrave someone's initals - at make717 we add this step to the project when hosting a group at our space, where the laser is right at hand.

Flashlight Gen 4.STL
Download View in 3D

Step 3: Electrical Parts List

As shown above:

Battery Clip, modified from a hard plastic T-clip.
Copy and paste these keywords into the search box at eBay:
9V 6F22 Black Battery Snap Connector clip Lead Wires Holder T-type Hard
Switch.The project is designed around a generic flashlight switch.
Copy and paste these keywords into the search box at eBay:
1A 30V DC 250V black Latching on off mini torch push button switch

300 Ohm Resistor, 1/4 watt.
LED, Water Clear White 5mm.
9V Battery (may be heavy duty or alkaline).

make717 does not endorse any vendors - use the one you like best!

Step 4: Modify the Battery Clip

Our battery clip is modified from a hard plastic T-clip, which comes in bundles of 100:

Pry the plastic cap from the clip using a small screwdriver.
Clip the two wires inside close to where they are crimped to the contacts.

TIP: Do this as busy work in front of the TV, and bag the clips for use later. The wires make great jumpers for your Arduino project.

Step 5: Prep the Switch

Bend one leg of the switch to match this drawing.

Step 6: Prep the Resistor

Bend one leg of the resistor to match the drawing. You can trim the leads to match the print, or solder it in place (next step) and then trim the ends, whichever works best for you.

Step 7: Solder the Resistor to the Battery Clip

Feed the bent lead of the resistor into the negative terminal (-) of the clip. That's the smaller of the two terminals. There should be a hole in the plastic at this end of the clip; the resistor goes through this hole as shown.

Solder in place.

TIP: Limit the solder time to 3 seconds or you may melt the plastic on the battery clip.

Step 8: Solder the Switch to the Battery Clip

Feed the bent lead of the switch into the positive (+) terminal of the clip. That's the bigger terminal. Also the one not connected to the resistor.

Solder in place.

TIP: Limit the solder time to 3 seconds or you may melt the plastic on the battery clip.

Step 9: Bend the Switch Into Final Position

Bend the switch until it touches the three posts on the battery clip. It should be centered between the battery contacts.

Step 10: Solder the LED in Place

Look at the picture, and make the connections to the LED:

Solder the long lead of the LED to the switch.

Solder the short lead of the LED to the remaining lead of the resistor.

TIP: Depending on how you prefer to work, it may be easiest to connect the short lead to the resistor first, and then trim the long lead to fit the switch. Or connect the long lead to the switch first, using it to position the short lead in contact with the resistor lead.

PRO TIP: The photo shows a small alligator clip holding the LED in place while the short leg is soldered. Saves burnt fingers and a lot of cussing.

Step 11: Test the Assembly

Snap the electrical assembly onto your 9V battery.

Press the button on the switch a few times. The LED should turn on and off. If it does not, go to the troubleshooting section and figure out what’s wrong.

Step 12: Assemble the Electronics to the Plastic

Assemble the case:

Slide the LED into the groove in the flashlight case (1).
Press the switch into the hole in the top of the case (2).
Snap the battery clip into the case (3).

The video shows how it's supposed to work.

9V LED Flashlight - Step #12
Download

Step 13: Done!

Check the flashlight for function.

If your flashlight doesn’t work, consult the trouble shooting section (next step).

You’re done!

An alkaline battery should last for about 25 hours. The LED will get dimmer as the battery runs down. You can use any 9v battery as a replacement.

Step 14: Troubleshooting

LED doesn’t light?

Check the LED leads - (+) goes to the switch, (-) goes to the resistor. The flat side of the LED body is (-).
Check the resistor - is it connected to the (-) contact of the battery clip?
Check the switch - is it connected to the (+) contact of the battery clip?
Check all solder joints.
Check for crossed leads (short circuits).
Using a multimeter, check the LED for continuity. It should conduct in one direction only.
Using a multimeter, check the switch for continuity. If it does not conduct electricity, press the button and test again. Expect a 5% failure rate on these switches, usually from overheating during assembly.
Using a multimeter, check the resistor for continuity. It should conduct electricity, and if you test its value, it should read 300 ohm.
Using a multimeter, check your battery. It should produce at least 1.5 volts. At 1.25V, the battery is officially dead.

PRO TIP: When building with a community group, assign one person to run the test equipment and send troubled flashlight builders there for service. That keeps the line moving.

Step 15: Bonus Step: a Jig for Assembling Flashlights

Because make7i7 does these in volume, we use a jig to simplify assembly. It's easy to make your own:

Find a chunk of aluminum for a heat sink. Our jig uses a slice of 1x3 heavy-wall tubing, about 1-1/2" (38mm) wide.
Modify a 9V battery clip by trimming away the plastic until it lies flat.
Use 2-56 miniature machine screws through each battery contact to fasten it to the heat sink. We clamp the contact to the sink, then drill and tap using the center hole of the contact as a guide.
Label the jig to reinforce correct placement of the electronic components. The LITTLE contact should be labeled SWITCH. The BIG contact should be labeled RESISTOR/LED. This is the opposite of the actual assembly, because the battery clip mates to the contacts on the jig.