Simple Squeeze Led Flashlight





Introduction: Simple Squeeze Led Flashlight

About: Tinkerer from childhood on. After my retirement, together with my wife, fully committed to creative production. I prefer simple solutions for non-existing problems.

Nearly 200 years ago Michael Faraday has discovered electromagnetic induction. A changing magnetic field produces an electric field in a coil. Today, there is a simple way to gain electricity from a relay and a strong magnet. I call this kinetic generator the RattleGen because, by pressing the lever of the relay quickly (the only moving part!) it makes a rattling noise. This electro generator is nearly solid state and produces enough energy to power a LED. Compared to 100 years of dyna flashlight based on a rotating generator, the RattleGen squeezer is nearly indestructible because of the few mechanical parts. This Ibble is part of an ongoing investigation for smallscale, batteryless energy harvesting.

Step 1: The Circuit

The electronic circuit is very elementary as you can see here. I use a resistor to reduce the LED current. Why do I call it an enhanced RattleGen? Well, doing experiments with a relay and a magnet, early 2013, I discovered on my oscilloscope screen a useful voltage. A ceramic magnet was put agains the relay coil. Pressing the contact lever made energy, as you can see in the video. A bit later I placed a strong neodymium magnet on the contact lever of the relay. As a result, the voltage was peaking 2 times higher on the screen. Then I took a small relay; the output peak voltage of the relay coil was 35 volt, without load. After the bridge rectifier the voltage peaks are smoothed by a condenser. To test the small generator I use an ultra bright LED. Take care; depending on the iron of the relay coil a stronger magnet will not give more flux, this because of the saturation. If you make the gap bigger between the contact lever and the relay coil the output will enhance. The magnet functions also as tension spring. The lever jumps back after pressing. This saves again one mechanical part. Before the LED light up you have to press the contactlever several times. The capacitor of 1000 microfarad 16 volt has to charge first.

Step 2: Some Remarks

Later, I will publish the test data at my website's energy blog. More experiments are necessary to optimize the parts; the results are already promising. This kinetic energy harvester can compete with the output of existing piezo generators and is much cheaper. Soon more applications will follow, with the RattleGen as starting point. My intention is that also people in developing countries can easily build this squeeze flashlight. And don't forget the young makers. Beside de fun of making this project, it shows them also one of the basic principles and needs of our present civilisation; electricity and light.



    • Water Contest

      Water Contest
    • Oil Contest

      Oil Contest
    • Clocks Contest

      Clocks Contest

    27 Discussions

    Hi there, I was wondering how frequently would you have to squeeze the lever, for example would it be possible (still functioning well) if it were integrated into the sole of a shoe so with each step the capacitor is charged or are footsteps too slow to charge the capacitor?

    If you shake the flashlight really fast, Can't it exceed the maximum voltage of the capacitor?

    1 reply

    The Maximum voltage of the capacitor is 16V. No way to exeed that voltage by fast squeezing. The only thing that happens is that the LED is going to light brighter. The voltage of the capacitor stays around 2.5 volt.

    If I create this, I still must put a little battery (CMOS ~ I think it's better for recharged) and IC that can run a little tiny dynamo repeated around 1 minute (we can find that inside a cell phone)

    Already try with Omron 12V but I just got 0.25V... Maybe must using Joule Thief to get enough power..?

    ~ 1 Vote for you :)

    1 reply

    Thanks for voting for me! The most important part for gaining energy is the relay. Use a 24V relay with minimal 1200 ohm coil resistance. The magnet I use is a ringmagnet 10x6mm with a hole of 4mm, power N48 with a holding power of 3kg. A joule thief and a voltage step-up converter like the ZXSC380 pull's min.10 mA. I connected both; they use to much current and make's the LED flashing.

    Thanks for this follow up on your RattleGen.

    I really must try it in a workshop with kids one day.

    For a workshop I would need about 20 relay I'm sure that will work, and scavenging that manny is not really practical.

    So I would have to try an buy them cheap. The cheapest car relays are only around 1 euro and that is right into the ally of my kind of workshops, but I'm not sure if those would be suitable. Any recommendation on which ones to buy and where?

    I would suggest adding a switch as well, to break the circuit when it's not needed, and to keep the capacitor charged up for quicker use the next time.

    Good that you remember me at this point. I place the list in the Instructable. Because the few parts and tools needed, you get it here. Parts: 1 small relay 24V (watch if the contactlever is useful), 1 magnet 8mm diameter 4mm thick, 4 diode's 1N4148 or 1N914, 1 LED, 1 resistor 47 ohm, 1 capacitor 1000 microfarad 16V and a piece of printboard. Tools: Soldering iron, thin solderwire, a wirecutter, an iron saw, mounting wire. That's it. Some relay's you can only open with a saw. Others you can take off the transparant cover. Look for a relay with a minimum of 1200 windings; 1800 is better. Success with building one!

    You could make it bigger and mount the magnet on a spring so that it oscillates more for each push.

    2 replies

    It is a step forward, when pushing results in more repetitious movements of the lever. Using mechanical oscillation or resonation to produce more pulses enhances de efficiency of the RattleGen. Clichej1, I like to tinker with spring's, this wonderfull objects. Maybe a new concept shows up. We keep in touch!

    Makes me remember some old ideas for converting omni-directional movements into electricity with magnets and coils like the concept of a shake flashlight but without the shaking. But i do not see how they could be useful on a bike since they would mostly rely on motion changes instead of direct wheel rotation.

    Should experiment on those ideas when i get up to date in my current projects.

    so nice..... maybe can be upgraded but the basic idea is so good !!!

    Great 'Ible. NEXT STEP PLEASE. In interest of those batteryless people, who also have no solar panels to power LED night lights/ no reading or working lights after dark....A more continuous lite source? I am thinking of the middle of Africa where they have cel phones (and few 6 or 12 volt rechargers) but no mains power. (PS: Africa is a really BIG place).

    So- How can I build a bigger little generator say- by making a circle of your wonderful simple little generators into a magneto type generator? This could then be cranked by hand to spin the magnets inside a circle of wire coils- or hung up with a flywheel-pulley- string and weight to run your LEDs for- what 10 minutes at a time?

    2 replies

    Dacarls - Great minds think alike! Check out

    I've asked about being a tester, but they've moved forward and are expected to sell these in mid-2014. I might need to get one.

    Still, I think you and I could each make a close resemblance right? That's what I'm planning to do! =)

    You ought to check out stepper motors.
    There are 2 types -
    pancake - stamped steel, cheap, higher losses.
    hybrid - laminated core, ball bearings, more expensive, low losses.
    Neither are terribly expensive.
    These can be turned by your weight / pulley method.
    Try the 24 V variety, as
    theyll generate useful voltage with less rpm.

    A very elegant little electronics project, nice job. You get my vote!


    I think I will make one. Here's my list of optimizations:
    High efficiency ultra bright LED
    Germanium signal diodes. They have an extremely low forward voltage drop so you can harvest more energy.
    Low voltage Super cap.
    Add a Joule Thief between the LED and the capacitor. Don't know if this will work or make it less efficient, but it is worth a try.
    A small solar cell with adequate voltage to pre-charge the capacitor somewhat for a quicker start.

    Thank's for the comments and suggestions on this project. First I want to explane some advantages of the RattleGen: High output by the way the magnet behaves; with a quick release and draw at the iron relaycore. The linear movement (only 0.1 inch) is more simple than a rotational. Also by small format still powerfull (fits in the heel of a shoe). No complicated electronic parts. Simple and cheap construction. Durable. No batteries needed. It is difficult to free our mind from thinking in rotational ways of power generation. Also from the use of non-sustainable (rechargeble) batteries. The reaction of guitarpicker7, to use a super capacitor is a better way to store the abundance of (kinetic) energy. The on/off switch is already part of the circuit.

    So now can we make something fit on a shoe so that each step trips the relay to charge a battery?