Intro: Scorpion Stinger - a High Power UV LED Flashlight
Scorpion Stinger features:
- Uses a re-purposed halogen flashlight that was acquired new for $10 which provides a plastic case with plenty of room inside for custom PCB's, a high discharge 3.7V 2200mA lithium battery, recharging circuitry, a trigger switch, a wall charger, and a car charger. What a deal for $10.
- The custom LED driver board sports 2 identical circuits that will boost a wide range of battery voltages (3V to 5 V) to a variable voltage output of up to 18 volts at a constant current of 200mA each circuit. The output current can be adjusted by a changing a single resistor. This switched mode boost power supply also has a feature of over voltage protection should the LED's become disconnected during operation. This circuit is easily adaptable to support PWM dimming.
***DANGER LITHIUM BATTERIES CAN EXPLODE OR CATCH FIRE IF MISTREATED OR SHORTED***
This instructable was submitted by the author, who is a member of the Xerocraft Hackerspace in Tucson, Arizona , for additional consideration for the "Instructables Sponsorship Program".
In the desert southwest of Arizona, scorpions are plentiful. Because they can squeeze into tiny of cracks, sometimes you find them in your house, too. For the good of all concerned, it is usually best to keep your property free of scorpions. Scorpion bites can be deadly to the very old, the very young, or people allergic to the scorpion venom. In recent news, a lady was bitten by a nasty scorpion and left her with a $83,000 hospital bill, with nearly $40,000 of that bill for the anti-venom alone.
Recently, our home owners association received complaints of a large amount of scorpions in backyards along a particular street. An exterminator found the source of the scorpions to be a large drainage ditch that was lined with large stones. These large stones made for a perfect scorpion habitat. Scorpions are notoriously difficult to kill using chemicals. The exterminator said that because the scorpion population was in a drainage ditch that was considered a waterway, and he could not treat this area with chemicals or risk the wrath of the EPA for dumping chemicals into a waterway. So, we were left to find another more environmentally sensitive solution.
Fortunately, scorpions are florescent and glow in the dark when illuminated with certain wavelengths of ultra violet light. It is really creepy to see, especially when they start to move. Since chemicals are not an option, it was proposed that periodic nighttime patrols of the ditches with UV flashlights would allow for manual scorpion collection. To test this idea, we went to our local drug store and purchased their largest UV flashlight that was marketed specifically for finding scorpions. It was tiny and the low light output made if difficult to sweep large areas of drainage ditch.
Clearly, a more manly UV flashlight was needed. We needed the Scorpion Stinger...
Step 1: UV LED Selection and Schematic
These LED's claim to have the following specs:
- UV LEDs with a wavelength of 400nm to 410nm
- 5 LED drivers per 10 mm LED module
- 40,000mcd (0.5W) output each 10mm module
- 3.6 Volt @ 100mA
- A nice tight 45 degree beam pattern means external optics or focusers not required
My circuit discussion for the functional blocks can be found on the JPG annotation.
Step 2: LED Driver IC Schematic
Texas Instruments has some very nice LED driver chips out there. TI also has a really nice web based circuit design tool called WebBench. I have attached the output of the WebBench tool that describes the operational electrical characteristics of the circuit.
The TI LM3410 was selected because it has thDuplicate circuite following features:
- Constant current driver able to source 250mA each IC
- Boost power supply ( 3.0V to 5.0V input yields up to 18 V output - perfect for batteries )
- Integrated switching IC (reduced circuit board parts count)
- Low parts count
- Very high efficiency up to 87%
- Unfortunately it only comes in surface mount
Step 3: Case and Battery Selection
- Disassemble light and recycle the metal reflector, light bulb, and glass cover.
- Remove the "guts" and save for later.
- A pistol grip case
- A high discharge 3.7 volt Lithium battery
- Charging circuitry
- AC wall charger
- Car charger
- Trigger switch
- Wrist lanyard
- Rubber lens bumper
- Lots of wide open real estate for custom PCBs or a second battery
Step 4: PCB Artwork
- Note the oversize LED copper pads for heat dissipation.
- Note that all parts except the 2 driver IC's are through hole.
- Note that the LM3410 IC has a thermal pad on the body of the chip itself, which is critical in getting the heat away from the chip. You might want to install a few heat vias around the LM3410 to conduct heat from the bottom layer up to the top layer (they are not shown in the artwork).
Step 5: PCB Toner Transfer
- Print your PCB artwork on the toner transfer paper
- Tape toner transfer paper to PCB copper clad
- Run through hot lamination machine
- Soak off the toner transfer paper in water
- Cover PCB with green TRF (toner reactive foil)
- Put PCB back through hot lamination machine to bond green TRF to toner
- Peel off green TRF plastic
- Trim PCB down to final dimensions
Step 6: Etch PCB
- Wear the proper protective gear. These chemicals are really nasty. I also use a respirator.
- Etch circuit board in etchant
- Stop etching process in a bowl of water
- Take the round LED PCB down to the final dimension. I used a wet tile saw. Don't dry sand or file circuit board material because the fiberglass dust from the PCB will get into your lungs and that is bad for your health
- Drill holes in PCBs
- Remove green TRF off of PCB with acetone
Step 7: Populate Custom LED and LED Driver PCBs
- Populate the circuit boards
- If you do not have plated through hole boards (home brew PCB will not), you must solder the top side of each LED in addition to soldering to bottom side.
- Start soldering top and bottom sides of those LED's in the middle and work your way out. This will allow the top side of the circuit board to dissipate the LED heat, too.
- I did not trim the legs of the LED's to allow them dissipate additional heat.
- Use your favorite cable/connector to join the LED board to the LED driver board. Make sure the wire is thick enough to support 200mA.
- The wire that connects the LED Driver board to the battery needs to be a heavy gauge. It will carry somewhere between 3 to 5 amps at times.
- Each TI LM3410 IC will only source about 200mA. Don't try to push them past that with this design.
- If the LED's start to flicker you either have a low battery condition or a heat problem with the LM3410 IC's.
Step 8: Custom Paint
Step 9: Final Assembly Part 1
- Install LED Driver PCB into the plastic housing
- Secure the LED PCB with a screw into the plastic housing. There is a hole provided in the PCB for this purpose that is aligned with a spot in the plastic housing
- Put the battery, charging circuit and trigger switch back into the plastic housing
- Attach battery to the LED Driver PCB. Cover the terminals, you don't want this to short out!
- Reassemble the plastic housing
Step 10: Final Assembly Part 2
- Install LED PCB into hole where reflector once fit
- Secure LED board from wobbling in the hole by using a few dabs of silicone adhesive or hot melt glue
- Reinstall black plastic retaining ring
- Reinstall black rubber bumper
Step 11: Applying Custom Graphics
- Design Graphics on your PC (or Mac)
- Print graphics using inkjet printer onto waterslide decal paper
- Cut decals to final dimensions
- Spray decals with a spray lacquer to seal in the ink. Do this in several coats with about 1 minute between coats.
- Soak decals in water for 30 seconds to 1 minute
- Slide decal off of paper and place onto plastic flashlight body
- With a towel wipe all water and trapped air-bubbles under decal
- Let decals dry for a few hours
- Overcoat decals with a layer of spray varnish (or spray enamel, although I have not tried spray enamel yet)
Step 12: Performance and Comparison Testing
Don't settle for any old small and weak drug store UV flashlight, you need the Scorpion Stinger.
The performance of the Scorpion Stinger was outstanding. It produced lots of good quality UV light, which the "Drug Store" UV light did not do. During 30 continuous minutes of field testing. the Scorpion Stinger behaved very well without any heat related issues.
A comparison test between the "Drug Store" UV flashlight and the Scorpion Stinger is very stark.
The Scorpion Stinger blows away the competition!
Step 13: Field Testing
With the Scorpion Stinger, the scorpions now fluoresce so much it is like they have a light bulb inside them.
These are a few photos after searching with the Scorpion Stinger. The bright green dots in the photos are the scorpions fluorescing in the UV light of the Scorpion Stinger.
Scorpion Touch and Run
Searching for Scorpions
Scorpion florescence demonstration
Step 14: Finished Product Views - Scorpion Stinger High Power UV LED Flashlight
Here are views of the Scorpion Stinger with custom graphics.
Since it is painted with glow in the dark paint, it really looks cool in the dark. The custom scorpion decal actually has the scorpion glowing in the dark because of the paint underneath.
Step 15: Future Development Work
There were some technical challenges that had to be overcome on this project. Most were heat related because of the LED lights or the extreme heat generated by the boost power supply.
In all cases, I felt that the use of a ceramic aluminum sub straight, instead of the standard FR4 fiberglass would have helped a great deal with the heat issue. However, this material is quite difficult to cut and work with. For this, a laser cutter would have been very handy, especially with custom shaped round circuit boards. The direct toner transfer method is good to make PCB at home, however the fine pitch of surface does pose a challenge. At one point when fixing a solder bridge on a SMD component, my soldering lifted a track. This track had to be replaced with a single strand of copper wire.
Boosting 3.0 Volts up to 15.5 Volts is no trivial task. This means that the supply current must be about 6-7 times the total LED current after you account for a 70% power supply conversion efficiency. The LED driver circuit is usually about 87% efficient, however the battery current draw was 1 Amp higher than I expected. Additional research is necessary, but "as-is", the circuit works fine with the battery at the current efficiency.
In the future, a CREE style UV LED Scorpion Stinger flashlight is planned. However, surface mount CREE LED's generate a tremendous amount of heat in such a tiny space that these must be done with circuit board material that has an aluminum ceramic to carry the intense heat away from the module with additional heatsinking on the opposite side of the PCB.
While using a boost switched mode power supply IC with an integrated switch did reduce the parts count significantly, it was more difficult to deal with the heating issues of the switch. While the circuit for the LM3410 IC behaves properly for the current configuration, there is no excess capacity in the design.