This project was inspired by another instructable called, No Nonsense Survival Kit by Instructa-Nathan. He made a survival kit that contained just about everything needed for survival and packaged in an Altoids tin. One thing I thought would be nice to have would be some kind of electric light like a flashlight.
The only problem for me would be that when I needed it, the batteries would be dead or expired.
So, I thought that if one could make a very compact solar flashlight, about the size of the tin box, it would be a good addition.
My idea is to use a glue gun to attach a small solar cell bank to the top of the Altoids tin and pack or cram an ultra-capacitor and LED inside the box. I do not have any Altoids tin to try, but I present my idea in the hopes that someone would be interested in miniaturizing the idea to the minimum size possible.
I'm presenting the parts and circuit to the best of my knowledge. I'm no electronics expert by any means, but have something that actually works and provides a small, but usable flashlight that provides useful, continuous light for about a half hour on a single charge of about 1-2 hours in sunlight. If used as a flashlight for short bursts as in looking for glasses on a tent floor or for putting something together in the dark, the charge and light would be useful for several hours. Maybe all night.
Step 1: Parts List
- Solar Cells - 2 x 5 volts 0.2 mw; Toy solar cells. I bought mine on eBay but do not see that they are available there anymore. I did find this link to some that are probably the same thing: aliexpress.com
- ultra-capacitor (super-capacitor) - available on eBay 5.5 V 4 F ultra capacitor
- 5 mm white super-bright LED from eBay, various sellers
- 1N4001 diode
- 82 ohm resistor
- push-button switch - momentary on, meaning that it is only on as long as you push the button, when released, the switch is off.
- solder type of breadboard - your choice; I used one similar to this from eBay 2 x 8 cm DIY PCB Prototype Circuit Solder breadboard
- hook up wire - 22 or 24 gauge is adequate; I use red for hot and black for ground and yellow for connections; colors are not important
Tools - the usual suspects
- soldering iron
- drill where needed
- solder paste
Step 2: Circuit Diagram
The circuit is simple and may not be exactly what an electronics engineer would provide, but it does work
Basically there are two solar cells in series. They are connected to the ultra-capacitor and have a 1N4001 diode that prevents the ultra-capacitor from losing its charge back to the solar cells when the solar cells are not producing electricity. Essentially, the diode switches the circuit to the solar cells off when not in use.
The LED has a "protecting resistor" of 82 ohms and is connected to the negative side of the LED. The positive side of the LED is connected to the ultra-capacitor positive terminal. There is a push button switch between the negative (ground) of the ultra_capacitor and the resistor. The push button switch is of the momentarily on variety. That is, when you push the button, the LED lights up. When you let go, the LED goes dark.
I happened to use a breadboard to mount the hardware. There is no need to do that, though. It works just as well to simply solder each component to each other in "dead bug style". That style would be much more compact to aid in fitting into a tight space.
I had a rather large push button switch for my prototype. You can use the mini push button switch just as well in the interest of saving space.
Step 3: Conclusion
This project was simply an extension of a previous Instructable by Instructa-Nathan as mentioned in the beginning. It is not meant to replace a normal flashlight. A single LED simply does not provide enough light to replace a real flashlight. The idea was simply to provide the survival kit with a simple and self-renewing electric light for emergency use.
I chose to use an ultra capacitor instead of a rechargeable battery, because ultra capacitors can be recharged hundreds of thousands of times. A rechargeable battery can be recharged about a tenth of that number and then it is dead. An ultra capacitor for all practical purposes never dies. The same with an LED instead of a bulb. LEDs last almost forever, bulbs have limited lifespans.
I chose solar energy to renew the charge on the ultra capacitor because it takes very little or no effort to simply place the gadget in a sunny area for a couple of hours. I have not tried charging the ultra capacitor on a cloudy day. Presumably, it would simply take a little longer to charge. Maybe several times longer. The solar cells I chose are very compact and quite powerful for their size.
Some possible uses: Flash the light at night to help rescuers locate the victim. Search for a dropped item in a small area. Read labels on medicine bottles or tools or gadgets.
Some statistics: It takes about an hour to two hours of bright sunlight to fully charge the ultra-capacitor. If the LED is on continuously, it will be very bright for about a half hour, after that it slowly dims. In an hour, it is too dim to be of much value except as an indicator, that could be a way to know where the flashlight and/or survival kit is located. It loses luminescence completely after about twelve hours.
Possible variations and improvements. A better electronic circuit would be welcome. I'm not sure of the efficiency or accuracy of values for components in the current circuit. Another improvement would be to make the entire flashlight more compact, so it would fit the Altoid box survival kit.
I would like to acknowledge Instructa-Nathan's encouragement and interest in having a flashlight for his survival kit.