Solar Engine Circuit Boards

As part of a project developed alongside the ETH Zurich Plant Science Creative Lab, we've been exploring BEAM robots or analog circuits that function based on simple inputs and outputs. They are often powered by the energy of the sun and like plant or insect life, can come in many shapes and sizes.

For this project, we've been inspired by the kits and projects of Solarbotics Ltd. and also indebted to Gareth Branwyn for his work in MAKE magazine showing some of the basic building blocks. Amos Blanton also contributed to the ideas of these boards through conversations and online prototyping. In the instructables community, TinkerJim's guides were indispensable. And of course this type of circuit board is based on the Tinkering Studio Circuit Boards and Scrappy Circuits.

In this guide, we're building a set of cardboard circuit blocks that can allow us to explore different assemblies that we can use later to make our own designs. We're still prototyping this idea so please share your questions, ideas and feedback in the comments.

Please also take caution when working with these electronic components and soldering. Wear safety goggles, if something gets hot, disconnect it and if you are unsure about adding a new component to the set please ask someone who has more experience working with electronics.

Prototyping time and R&D with for this project was made possible through a collaboration with Universität Zürich - ETH Zürich - Universität Basel, Plant Science Center.

For this project, you'll need to collect the following supplies:

• Cardboard
• Copper Tape
• Trigger MCP112-270E
• Transistor 2N3904TA (NPN)
• Transistor 2N3906-G (PNP)
• 3 6.3VDC 4700uF Capacitors
• Solar Cells (we use one that has 3.4V and 12mA output)
• Alligator clip wires
• Pager Motors
• Gear Motor
• Color Changing LEDs

You will also need the following tools:

• Soldering Iron
• Solder
• Heat shrink
• Safety Goggles
• Hot Glue Gun (optional)
• Round nose pliers
• Wire snippers

And finally since this activity relies on solar energy, you'll need access to the sun or a bright light source.

Capacitors play an important role in the solar motors. They store the energy that's produced by the solar cell and then, when enough energy is saved up, they release the power to the motor. This allows the system to continue to work in low or unreliable light.

For this project we're using three 6.3VDC 4700uF capacitors. Before using another type of capacitor please check with someone who has experience with electronics and can offer advice. We recommend staying at or below 6V to be safe.

To build the block, cut out a piece of cardboard that's approximately 10 cm x 4 cm Place two strips of copper tape about 2 cm apart from each other all the way to each end of the piece of cardboard. Connect the three capacitors to the lines (either by soldering or with extra pieces of copper tape), making sure to keep the polarity in the right direction. The capacitors should have a stripe on one side to let you know which side is positive and which side is negative. You might want to label each of the two sides of the copper strips with a pencil so that you can keep track of the polarity later.

The solar panels that we're using for this project provide 3.4V and 12mA. You can test our different types of solar panels to see how they react in the system. It's also possible to dissect elements like garden lights, calculators and toys that use solar cells and reuse the panels in your experiments.

For these projects you can also use a wide variety of DC motors. These motors include small pager motors that vibrate, hobby motors that spin fast or motors with a gear system that makes the motor move slower and have more strength.

For each of these elements you can add alligator clips so that they can be easily attached to the other cardboard blocks. Cut an alligator clip wire in half and strip the wire about 4mm from the end. Twist the wires together and solder them on to the leads of the motor or the solar panel for easier prototyping.

For this project, we'll use an analog circuits to control the solar engine. This means that we're using some electronic components in a specific arrangement to accomplish a task without programming a circuit board.

We're using two different types of transistors, which are components that amplify or switch an electrical signal. These have three 'legs' (or wires) coming from a half cylinder shaped 'head'. We're going to refer to the parts as if you were looking at the transistor with the flat side with the text up and the legs facing down. We'll refer to the legs as left, middle and right but also by their technical names emitter, base and collector.

For the 112 trigger, which provides a signal to release the energy stored in the capacitors, we'll just call the legs left, middle and right when looked at from the same orientation.

If you want, you can add little sticker dots, white-out symbols or nail polish to the bodies to more easily tell them apart. As well you can use a sharpie to color the legs if that can help to make it a bit less confusing.

Cut a piece of cardboard approximately 16cm by 14cm

Take one 3904 transistor, one 3906 transistor and one MCP 112 trigger. Gently spread the three legs of the components apart.

Put a piece of copper tape approximately 8cm long in the middle of the piece of carboard. Place the 3904 transistor facing up on the right side of the line of copper tape with the legs facing to the right. Solder (or use copper tape) to connect the middle leg of the 3904 transistor to the left side of the copper tape.

Place the 3906 transistor facing up on the right side of the copper tape. Turn it so that the legs are facing up. Connect the right leg of the transistor to the right side of the copper tape.

Next place two 3 cm strips of copper tape above the initial piece (leaving a space for the resistor). Solder the right leg of the 3904 transistor to one side and the middle leg of the 3906 transistor to the other side. Connect the 1k resistor in between the two pieces (the direction doesn't matter here).

Place the 112 trigger element under the initial strip of copper tape with it's legs facing up. Use copper tape to connect the right leg of the trigger to the left leg of the 3904 transistor. Use a piece of copper tape and solder to connect the left leg to the middle strip of tape.

Now place a strip of copper tape on the right side of the piece of cardboard so that it runs underneath the left leg of the 3906 transistor from the top to the bottom of the cardboard. Place a piece of paper or cardboard over the line from the 112 trigger to the middle copper tape to form an insulated bridge. Using a piece of copper tape, connect the middle leg of the 112 trigger over the bridge to the line of copper tape on the right side.

Extend out the copper tape down from the left leg of the 3904 transistor and up from the right leg all the way to the edge of the cardboard.

Now that you have all the parts assembled, bring your boards outside or into a brightly lit room where you can experiment.

To make the simplest solar circuit, connect the negative side of capacitor strip to the bottom left line of the engine trigger (where the 3904 and 112 connect) and connect the positive side of the capacitors to the bottom right shared line where the middle leg of the trigger and left leg of the 3906 connect).

Connect a solar panel to the other side of the capacitor strip (making sure to put negative on negative and positive on positive).

Finally connect one side of the motor to the copper strip on the top right (on the shared line where the middle leg of the trigger and left leg of the 3906 connect) and the other side to the top left where the middle pin of the 3906 connects to the right pin of the 3904 through the resistor. Place something on the motor so you can see or hear it move.

Place your circuit assembly in the brightest light you can find and notice what happens. Depending on how much sunshine you have, you should eventually see the motor turning on and off intermittently. If nothing happens in 5 minutes or so, go back and look at the diagram and make sure everything is connected how it is supposed to be. Also check your solders or taped connections to be sure that there's solid contact.

Here are a few other things to try or questions to ask:

How does the system work in different light conditions?

Can you power more than one motor?

Does adding more capacitors change the system?

Does adding more solar panels change the behavior?

This is a real electricity experiment and things can go in unplanned directions. Please wear safety goggles when working with the solar engine circuit elements. If a part gets hot, disconnect it right away. If a capacitor or other component breaks or bursts, discard it and make a new one.

Once you have this basic set of materials to explore, there are many other things you can do to continue your experiments:

You can build the solar engine circuit assemblies in different arrangements, shapes and sizes to fit your project needs. As well you can experiment with materials and connection types. We'd like to make circuit block style elements on wooden blocks for more a robust testing kit.

You can try out different values of resistors or solar cells. As well you can experiment with different types of outputs including scrounged motors, LEDs and speakers.

And once you have experimented with the basic components, you can start to incorporate these designs into a fully-fledged plant or insect like robot that takes energy from the power of the sun and converts it into movement, light or sound. You can take inspiration from scrappy automata (https://wonderfulidea.co/blog/2021/1/11/cardboard-...) or kinetic collages (https://wonderfulidea.co/blog/2021/5/4/servo-colla...).

Let us know what you try and what questions you have! We'll continue to update this instructable with new examples ideas and inspirations as we continue the collaboration with the ETH Zürich Plant Science Center, Creative Lab and other makers and tinkerers.