The Kit:

This instructable is based on a kids science project that I am doing in a few days time with my daughter and a few of her friends.  It's simple and fairly quick to do so although it does involve some soldering I don't expect that we will have trouble doing this with our small group of carefully supervised 7-year-olds.

The idea for this project was inspired by this article over at Evil Mad Scientist although the circuit is modified to be a little more efficient.  Because it's made up from a simple set of parts it would make an ideal beginner's electronics kit.  I'm therefore putting this forward into the "kit" challenge as well as the education comp'.

This kit could be used for an introduction to science and electronics from ages of about 7 upwards.  It requires some simple through-hole soldering and employs batteries and a solar pannel, which might be at the level of a young junior school child.  However, it also uses a diode, which is a slightly more sophisticated concept, both NPN and PNP transistors and so could be the basis of an introduction to transistors and it uses a blocking oscillator in the "Joule Thief" part of the circuit which could be used to illustrate inductance at a higher level again.

There are many learning points at different levels from this kit:

At the lowest age group (say 6-9 years) I'm using this as an introduction to the concept of circuits, to soldering and to very basic components (see final step).  I'm not formally a teacher but I have been running young kids science projects for a few years now and they tend to be well received.

At a somewhat older age (say 10-14), this could be an introduction to discrete semiconductors - to diodes and transistors.  Towards the top of this group one might discuss NPN vs PNP transistors at least from a functional point of view.

At an advanced stage (sat 15+), this could be used to illustrate advanced electronic concepts such as inductance and the correlation between electric and magnetic fields.  A more theoretical consideration of semiconductor doping and the function of diodes, LEDs and NPN vs PNP transistors would also be suitable.  The LED and low Vf diode in fact allow discussion of band gaps and some quantum mechanics if appropriate.

Green Tech:

This is a nice, sustainable-energy kit, with all the power for the lamp being sourced from renewable solar energy.  It uses scavenged jam-jars as the enclosure but could also use some scavenged parts such as toroids from old CFLs


This is a small simple and low-priced kit with a wide range of learning points.  It's green, it looks cute and works at the end of it!

Edit March 2013:
I've been working with Joshua Zimmerman over at browndoggadgets.com to make these little boards available through his site.  Leave a message if you're interested, or pop over there and see if he has them up yet.


Step 1: Kit and Parts

The parts that you will need are:


5V 70 mA Solar pannel (around 60x60mm)
Twin AAA-size battery holder
2 AAA-size NiMH rechargable batteries (around 1000 mAh works well)
Circuit board (see last step for Eagle files)
2N3906 general purpose PNP transistor (or equivalent)
2N3904 general purpose NPN transistor (or equivalent)
1N5817 low forward voltage schottky diode (general purpose - e.g. 1N914 - diode would probably work)
Slide switch
Ferrite bead/toroid (scavenge from an old compact fluorescent lamp if you only need a few)
LED (high brightness - diffused ideally but I only had water-clear so scratch it up with sandpaper)
22K resistor*
4K7 resistor*
1K resistor
1nf ceramic capacitor (some parts of this 'ible refer to a 2n2.  Either seems to work fine)
30 cm 22-guage solid copper wire (from an old ethernet or telephone cable works well)

Optional items::

Old (empty) jam or pickle jar to house your circuit (we will assume you are using this).
Sparkly things (e.g. acrylic jewels) for the bottom of the jar (makes it look pretty)
Glass paints (could be included in kit)
Small double-sided sticky pad (optional but useful)


Soldering iron & solder
Drill press or punch
Hot glue gun & glue (epoxy would be fine but slower).  I use low-temp hot glue with the kids.
Metal file
A little tape to hold things in place
medium grade sandpaper (tiny bit)
Helping-hands type tool also very useful

* These resistors may need adjusting depending upon the performance of your solar cell and LED.
The 4K7 and 22K make a voltage divider that controls the light level at which your LED comes on.  Increase or leave out the 22K for darkest switch-point.  Decrease the to switch on when it's lighter.  But be careful - depending on your solar cell you may need a pull-down to make the PNP switch on fully.  A 100K trim-pot would probably work well if you wanted to control this.

I see that you used 2.4V. Would it work if 1.2V was used?
It should but I have not tried it. Certainly the JT circuit will light an LED from a 1.5V alkaline AA so I should be surprised if it didn't work off a 1.2V NiMH. <br> <br>The issues with this might be: <br> <br>The 5V solar cell is overkill for a 1.2v battery. Go for something closer to 3-3.5v. That might mean you need to use a higher current panel but a AAA can only take around 100mA max. <br> <br>The more the JT has to boost the voltage the more current it will draw (the energy has to come from somewhere). As a result, one AAA would probably not store enough energy to be reliable. If you were going with one cell, I would use a AA. This would also alow you to use a higher current solar panel (maybe up to 200mA). <br> <br>You may find that it is not so bright, but at the moment it is really bright so that might be OK. <br> <br>I don't have all the parts to test a 1 x AA setup but I will test the JT part when I have the time and let you know. I'm pretty sure itwill work fine. <br> <br>Ugi

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