# Magnetic Circuit Blocks

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## Introduction: Magnetic Circuit Blocks

Nothing is better for learning or designing electronics than building real circuits. The breadboard is a popular option but it often results in an incomprehensible spaghetti that has no resemblance to the original schematic and is hard to debug.

I took inspiration from another instructable to make a set of magnetic blocks that can be combined into electronic circuits. The result is awesome: basic circuits are set up in seconds and they look just like the schematic! The connections between the blocks are very reliable since the copper strips of two different blocks are pushed against each other by the magnets under the tape.

The blocks are made from recycled cardboard with small magnets on the borders. Copper tape cover the magnets and connect to the components. By putting two small magnets on each border, the blocks always attract. No specialized tools are needed, and the cost is circa 10 cents per block.

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## Step 1: Material

100, 200 or 300 cylindrical neodymium magnets of, 5mm diameter, 1mm thick (5x1mm). These are readily available online for ~1.5 cents a piece (e.g. here)

10mm wide copper tape, a 10m roll will be more than sufficient (e.g. here)

Strong cardboard: the 6mm 3-layer version is good. 50x50cm is more than enough

Components for prototyping: a 4xAAA battery holder, LEDs, resistors, capacitors, transistors, a speaker, an LDR, buttons, a potentiometer etc. In the next step is a detailed list for a minimal set.

Tools: a box cutter and a soldering iron. Red and blue permanent markers. Tweezers are handy for bending pins.

## Step 2: Minimal Set Using 100 Magnets

Here is a suggestion for the components to make 23 blocks with 100 magnets:

4 straight connectors

4 angle pieces

2 T-junctions

1 battery box

2 LEDs (green and red)

4 resistors (100Ohm, 220Ohm, 10kOhm, 22kOhm)

1 potentiometer (10kOhm)

1 LDR (light-dependent-resistor)

1 npn transistor (e.g. 2n3904)

1 electrolyte capacitor of 100muF

1 button

At the end of this instructable, there are 11 easy circuits shown that you can make with this minimal set.

## Step 3: Mark the Poles of the Magnets

The cylindrical neodymium magnets have no marking of the north and south pole, but keeping track of the relative polarity will be essential to make the circuits blocks always attract.

The easiest way to find out is to revert to the definition: north is the pole that points to the north when the magnet is left free to rotate: squeeze a thin wire halfway the stack of magnets and lift it up: like the needle of a compass, it will align with the earth magnetic field. Check for consistency at a few different locations, then color the north pole red, the south side blue.

Stick all magnets with the north pole up on an iron sheet (e.g. cookie box). Color all sides red with a permanent marker. Let it dry well for 10 mins, turn them around and color the south pole blue. Now all magnets are marked according to the common convention (red=north pole, blue=south pole)

## Step 4: Cut the Cardboard

With a pencil, draw a grid of ~100 2.5x2.5 cm squares. Add also one ‘strip’ of 5.2cm: double-unit blocks need to be 2mm wider than two single-unit blocks to account for the two magnets of 1mm each that separate two blocks. Three ‘units’ becomes 7.9cm. Cut the blocks into 2.5x2.5 squares, but also make some 2.5x5.2cm rectangles for long connectors and 5.2x7.9cm for large components like the battery holder of a speaker.

## Step 5: Attach the Magnets With Copper Tape

Cut some copper tape of the correct length for each block:

Connector block: 4 magnets, 5cm tape
Long connector block: 4 magnets, 8cm tape
Angle block: 4 magnets, 2 pieces of 3cm tape
T-junction: 6 magnets, 1 piece of 3cm tape, 1 piece of 5cm tape
Cross-over: 8 magnets, 2 pieces of 1.5cm tape, 1 piece of of 5cm tape
2-terminal component: 4 magnets, 2 pieces of 2cm tape
3-terminal component: 6 magnets, 3 pieces of 2cm tape

Group the magnets in pairs, where each pair has one blue side up and one red side up. They will attract slightly in this configuration. Remove the paper from the copper tape and stick it on the magnets leaving ~5mm free on the side that will go on the bottom. Stick the tape on cardboard square such that the magnets are on the side of the block. Beware of the orientation: on the top side, blue should be left and red right. On the right side, blue should be up, and red down, and so on for the rest of the square: this will guarantee that whenever two blocks come in contact, a north pole from one block faces the south pole from the other block and they always attract, even when the blocks get rotated.

For the 3-terminal components, the copper tape may overlap, and they need to be trimmed: cut them delicately with the box cutter and with sharp tweezers the excess tape can be removed. Excess tape for other blocks is also removed this way.

## Step 6: Solder the Angle Blocks and T-junctions

Two pieces of copper tape stuck on top of each other may look like a great connection, but remember there is a layer of glue in between, and they usually do not connect electrically! To make a robust permanent connection, solder a drop of tin that connects to both pieces of tape of the angle blocks and the T-junction.

## Step 7: ​Mount the Components

With a needle, punch small holes where the leads of the components will go. Cut the leads to the right length. Let the component stick out 1 or 2 cm, that way it will be easier to place and replace the blocks. Stick the component though the holes and solder the leads. For resistors and capacitors, write the value on the block. Indicate with symbols and colors other properties of the components or connection, such as the polarity of the elco and LED.

## Step 8: Try Out Some Simple Circuits

In the pictures there are 11 circuit ideas for the minimal set M100, try them out!

Using a larger number of blocks, more advanced circuits can be built. The videos show:

• A 2-transistor multivibrator (double flash light)
• A 2-transistor bistable multivibrator (flip-flop, or 1-bit electronic memory)
• An RC oscillator

## Step 10: Joule Thief

An interesting circuit: a single 1.5V battery lights 3 LEDs in series! The special component here is the self-wound transformer: 80cm of 0.2mm enameled wire bent double and wound 20x through a ferrite ring (10mm outer diameter, 5mm height). Note the dots on the transformer block: it indicates that the left windings run in the opposite direction of the right windings. The Joule thief is a self-oscillating voltage booster and it can squeeze the last few Joules out of a battery that is normally considered dead: it will work down to ~0.5V. There are plenty of instructables dedicated to this circuit, e.g. from electronicGURU, 1up, ASCAS, Jason B, etc

This is an entry in the
STEM Contest

## Recommendations

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## 7 Discussions

Thanks for the compliment! I think these circuit blocks compare favourably to the scrappy circuits. I'm now using the blocks for actual prototyping. Yesterday I added the Joule thief as step 10 to the description. It's a high-frequency circuit (~100kHz) and there are no problems with stray capacitance or stray inductance. In minutes I could make and evaluate several variations of the circuit (LEDs in series, vary the base resistor, add resistance to the battery etc)

Very nice idea, a fun way for kids to learn with readily available (recycled) materials... and a lot cheaper then for instance snap circuits and similar educational Stem toys, which makes this available to everybody and not just the privileged.

Thanks! Indeed, contrary to the commercial sets, if you miss a crucial component for an interesting circuit it's made in 2 minutes. And the quality is just as good if not better. If I find a 5mm think 25mm wide wooden beam, I might try a wooden version as well.

Nice, I'd love to see it :)

Great job, very inspiring and creative. One suggestion. I think you could cut down the complexity and need to solder with very little impact on construction material cost using copper tape that is dual conductive (on both sides including the adhesive).

Very awesome! And best of all! Cheaper than those available in the market.