Perhaps this is more of a mechanical engineering question than electrical engineering. I spent tons of time on it and came up with solutions that sorta work, but do not scale at all. I was hoping someone can help us with this predicament.
I need to find the easiest and most reliable way to make two surfaces conductive when pressed against one another. Why? I have Lego pieces of the large variety (2" x 2"ish) that are modified internally to have wires connected to opposite faces . The right face is connected internally to the left face and the front face is connected internally to the back face via fine wires. The internal connection forms a '+' like pattern, if that makes any sense. This was accomplished by drilling fine holes through the 4 sides of each cuboid and threading wires through them. The idea is for children to place such Legos adjacent to one another on a Lego surface and form various electrical tracks triggering lights, fans to turn on...etc. I need each two Lego pieces that are touching to be conductive. For example, if I place 10 Legos in a single row, then a current could flow from part 1 all the way to part 10 passing through all the pieces in between.
The struggle we I am facing is in the choice of material to use on the outside surfaces to make the faces conductive. So far, I tried using small pieces of Copper conductive tape and even Nickel battery strips. They "do work" but they peel off really quickly and fail constantly. I also experimented with neodymium magnets, but they seemed barely conductive not to forget how lethal they are if swallowed, especially by children. I combed Digikey and other sites for some sort of spring loaded contacts. The only parts that showed promise are pretty pricey at more than $4 each. Remember, I need 4 per piece. Do you any suggestions that you think could work?
Things peel off because you did not use an adhesive appropriate for the type of plastic you are using. Get an adhesive to match the plastic and the copper you tried, or even aluminum foil
You can use bullen-nails for non-abrasive contacts. Wires solder well to brazen nails.
Many years ago I used poppers (patent fasteners) for making contact between components. They give good and persistent contact if you solder the copper wires to the poppers. A bit different from Lego pins, though.
if you look at the LittleBits, they use magnets, just like the Brixo parts, but there are multiple supply outlets for them. but seem expensive.
another option is to use sheet metal, cut slots into your plastic and then plastic weld the metal in place.
another might be to use wire. Electrical + could be wires running top to bottom, and - could be running lenghtwise.
google " integrated circuit building blocks " for some similar stuff on aliexpress.
these seem to use only top and bottom connections and not side. much less expensive. but no idea of the design or quality.
mechanically, conductive chrome seems to be what is on the end of batteries and magnets.
dave-in-nj:
if you look at the LittleBits, they use magnets, just like the Brixo parts, but there are multiple supply outlets for them. but seem expensive.
another option is to use sheet metal, cut slots into your plastic and then plastic weld the metal in place.
another might be to use wire. Electrical + could be wires running top to bottom, and - could be running lenghtwise.
google " integrated circuit building blocks " for some similar stuff on aliexpress.
these seem to use only top and bottom connections and not side. much less expensive. but no idea of the design or quality.
mechanically, conductive chrome seems to be what is on the end of batteries and magnets.
Thank you so much Dave. This is very useful. I will take a look at the magnets option for now.
You don't solder them: make the wires come through the surface, and spray on them.
Two potential issues.
contact side to side is based on pressure, must have a way to maintain this. Brixo used small spring-like contacts for that in the ends of the bricks.
rubbing of the bricks (when constructing/breaking apart the circuit) may make the coating wear off quickly, especially a concern in light of the above.
wvmarle:
You don't solder them: make the wires come through the surface, and spray on them.
Two potential issues.
contact side to side is based on pressure, must have a way to maintain this. Brixo used small spring-like contacts for that in the ends of the bricks.
rubbing of the bricks (when constructing/breaking apart the circuit) may make the coating wear off quickly, especially a concern in light of the above.
That makes total sense. Thank you so much for pointing out these issues. I might look into using battery terminals of something else of that sort.
Brixo's design very much looks like battery terminals to me indeed.
But mind that those as used in battery holders are also not designed to have batteries replaced a thousand times, or for child-proof robustness. Especially the spring side (negative terminal) is not robust. I don't know what material they use; maybe stainless steel? At least no thin surface to corrode, but it's also not solderable so harder to connect wires to reliably.
how about machining a pile of Lego bricks out of metal?