Copper Foil Connected Lego Block Circuit

In the past I used to have one of the solder free plug and play electronics kits that now can be found in a number of forms.

Whilst in the process of reminiscing the thought of making my own came to mind.

What form will it take, base plate with socket, pins or nuts and bolts, what about the components, on stripboard, PCB or air wired on Perspex or a 3D printed carrier, all would have been possible but then the Tin foil competition was launched and it became clear.

The interconnections would be made with Copper foil tape, its conductive can be easily formed, cut and soldered, whilst at the same time it needs to be reconfigurable.

But where would the tape be used on the base plate on the components or both.

In the end I decided that the tape would be used solely on the component carrier with the component soldered to the tape.

This would mean that the base plate would simply be a support with no electrical connections.

The connections being made by the intermate contact between the carrier faces.

Using a square carrier meant that there were 4 sides with which to make contact, the base of the carrier would simply lock to the base and the top surface would be used to mount the component.

So now I needed a square carrier that will allow tape to be mounted on four sides that will support a component and enable reconfigurable attachment without the need for tools.

After thinking about various methods an opportunity presented itself in the form of LEGO, the 2 * 2 blocks fitted the bill for the carrier, being easy to handle and uniform making layout easy additionally base plates existed in a variety of sizes to suit a range of circuit sizes.

A bonus was in the variety of colours which allowed component types to be easily identified by colour coding.

The colour coding adopted:

White - wire links

Yellow - Indicators

Blue - Capacitors

Green - Transistors

Red - Resistors

Colour codes were chosen based on what I had available.

If more colours are available differentiation could be applied to the wire links and in addition the part type reference could be added for another means of identification.

I just needed to put the idea together in physical form.

Copper foil adhesive tape 250 cm long * 12 mm wide

45 (2 * 2), blocks

7 * 8 (2 * 2 block) area, 120 mm * 128 mm

Component block.

2 * LED (yellow blocks) - red LED's

4 * Resistors (red blocks) - 2 * 470R, 2 * 47K

2 * Capacitors (blue blocks) - 2 * 10uF/16V

2 * Transistors (green blocks) - 2 * BC109C or equivalent NPN transistors

Interconnect link Types (white blocks)

2 * P4 (4 connection link common head pin)

17 * L2 (2 connection link)

13 * L3 (3 connection link - T shape)

3 * XU (cross under, 2 isolated links)

1 mm drill bit and drill.

Scissors.

Wire cutters.

Pointed nose pliers.

Pencil or other visible marker.

Fine (0.4mm), tip long soldering iron bit or similar.

Solder.

Soldering Iron.

Flat ruler or tape.

22 AWG tinned copper wire.

22 AWG enamelled copper wire.

I would need a circuit with which to determine the required elements rather than randomly creating a stack of elements then look for something to build.

This meant I would only build the required elements for the chosen circuit, but which circuit?

For this first incarnation I would use discrete components with no more than four pins, fitting for the following resistors, capacitors and transistors essentially the basic electronics building blocks.

It is not to say that more complex devices could not be supported it would just require a departure from the 2*2 block. (The 2 * 4 block would enable an eight pin IC to be accommodated for example), but that's for another project.

The circuit chosen was a previous Instructable Disctrete_Chain_Link_Oscillator with full details of operation.

Now that I had decided on the circuit I would need to lay it out using blocks.

The components would simply have one connection per side.

However, suitable links would need to be provided to keep the layout to a small size, resulting in a range of links for different purposes.

1: A block where all 4 sides are interconnected having a common top side connection. Named P4 to indicate it has an external pin connection for applying power or measuring a node whilst also connected on all 4 sides.

2: A straight link with 2 connections on directly opposite sides. Named L2 for 2 connection link.

3: A 3 way link were 3 sides are interconnected. Named L3 for 2 connection link

4: 2 straight links at right angles to each other which are electrically isolated from each other. Named cross under as one link crosses under the other one.

Using these link combinations, connections can be made to nodes not directly opposite or which have circuit elements between them.

I would now need the following :

45 blocks - 2 Yellow, 4 Red, 2 Blue, 2 Green, 35 White (P4 * 2, L2 * 17, L3 * 12, XU * 3)

From the layout design the blocks were laid out in their designated locations.

With a pencil I drew the link and component orientation on the top.

Then with a 1mm drill bit in a hand drill I made holes in all the blocks, the number of holes per block being based on the element assigned. Holes were made equidistant between each pair of pegs were required.

The foil tape which is 12 mm in width was cut into 20 mm lengths, one length per side of a block.

Each piece of tape was marked half way (6mm), into the width and 5mm in from the short edge.

This point is tinned with a spot of solder were the lead of the component or link will be attached.

115 lengths of tape will be required to form all the connections.

The required component is matched with its corresponding block and inserted into the appropriate holes.

The legs of the component are bent into position on the inside and pressed flat against the side with pliers.

Next one of the previously prepared copper foil strips is inserted between the component lead and the inside of the block (adjustment of the lead may be required to enable the strip to slide in).

Ensure the strip is inserted adhesive side against the block side wall and soldered point against the wire.

Make a packing strip out of 40 mm of Copper foil tape and fold it in half so it 20 mm long.

Insert the packing strip between the previously inserted tape and the inside of the block.

The strip will add some protection against melting the side wall of the block when soldering the lead, whilst improving the thermal contact between the lead and the tape, making for easier soldering and a more reliable joint.

Then solder the lead to the tape at the pre-tinned location using a long tipped fine (0.4mm) bit or similar.

The central cylinder in the block is likely at some point to suffer contact with the soldering iron, this is not an issue for minor melting. To negate this issue a tubular guard can be made from the copper foil tape which can be slid over the cylinder for protection.

Once the lead has been soldered to the tape, remove the packing strip and peel the tape from the backing strip being careful not to tear the foil.

A scalpel carefully run between the tape and the backing strip will aid removal and prevent tearing of the foil.

The heat from the soldering iron will also soften the adhesive aiding removal.

Once the backing strip has been removed press the soldered point down against the inside of the block.

Pressing the tape down either side of of the soldered point first can result in tears in the foil as the soldered area is rigid and resists flexing.

Bend the tape around to the outer side of block, press the side against a flat surface to flatten the tape and trim off any overlap with a scalpel.

Where you have three or four connections you will need to trim between 1 or 2 of the tape strips thinner to ensure they do not cause short circuit between adjacent sides

Check the continuity with a DMM or other appropriate tool to ensure there is a good joint.

All that is required now is to repeat the process on every block.

Once all the blocks have been completed they need to be assembled to create the circuit previously defined.

If after assembly and powering up it fails to work check the following:

Apply pressure to the top and/or sides of each block in turn to check for intermittent contact.

If this does not resolve the issue power down and perform a continuity check for each element to its immediate neighbours to check for a bad contact.

Poor contact can be remedied in a number a ways such as:

1: Re-soldering the original joint if it was poor (weak/high resistance).

2: Applying a spot of solder to the centre of the tape, make sure this is only a thin layer other wise you will end up with a skewed block and possibly a worst problem.

3: Applying a second layer of tape on the affected side but make sure this is soldered to the first layer otherwise you will be creating an open circuit as the adhesive can prevent contact compounding the problem.

If all went well either immediately after assembly or following a debugging process, congratulations.

You have now created your own electronics kit.

By simply building additional elements you can create different or more complex circuits.