For this application I would mount the breadboards and displays neatly on a board and use solid insulated 22 AWG tinned wire cut to exact lengths to neatly make connections flush with the breadboard, with right angle bends in the wire and little or no overlapping. The 22 AWG wire will make a pretty firm connection with the breadboard springs and since you don't have the jumpers acting as levers it's more reliable.
I would like to have a common rail of ground to which to clamp each individual ground, including the source one ("Thunderstuk").
You could use a bus bar, something like this:
Because I want to show all these items to children, I am now allowed by law to use PCBs.
I only have 1 mm (18 AWG) wires of different colors. In 18 AWG (around) I only have blue and white wires.
Can I use the 18 awg ones?
I have no precise legal reference, but a friend of mine was not allowed to hand over electronic components to children because the Inspection considered them as dangerous for the kids (10-14 years old). "sharp terminals" - they said. :-(. PCBs means soldering, you see.
You might have trouble even getting the 18 AWG into the breadboard. If you do it will probably stretch out the spring contacts and cause those sections of the breadboard to no make a tight connection with smaller gauge wire (such as resistor leads). However, if this is intended to be a permanent installation then that would not be a problem and certainly the 18 AWG will be quite resistant to wires getting knocked loose.
I suppose regulations will vary depending on where you are located, but the BBC distributed a million micro:bit PCBs to 11-12 year olds in 2016. I'd say the UK would be one of the more strict countries regarding safety regulations. In fact, the original plan was to give them to 9-10 year olds but they changed the age target, not due to safety concerns but due to finding that the older kids were more likely to continue using it outside school:
So certainly I don't think it's accurate to say "PCBs aren't allowed for kids". Now the micro:bit is all surface mount so you don't have the sharp lead ends sticking out the other side of the PCB but actually if you cut the leads off to the right length you can tent them over with solder and there is no sharp point. Perhaps it's not quite as good a joint but I think it will be quite good enough, especially when compared to the typical SMT joint. And of course the micro:bit is using lead free solder.
I suspect here it is all about safety paranoia, not about observing an actual legal constraint.
There is however a problem with the chemical content of some components. I faced it when I attempted to dismantle old PCs together with the children. The procedures calls for the PCs parts manufactures to take out themselves the components that are listed as dangerous (before PCs given to the kids).
I truly believe that a campaign shall be started in respect of children safety to clear the false legal issues or to remove the excessive legal provisions - as the case may be- throughout the European Union.
I also suspect that in some cases is only about excessive interpretation.
I guess I am off-topic, but this is a an interesting subject.
Concerning the most appropriate kids age to learn and continue use of Arduino at home.
I have some experience in teaching kids advanced science. In my opinion, is all about teaching method. I taught 9-10 years old kids hexa and binary, half-adder, pn junction etc. It can be done, but the method (and the pedagogy behind) are very specific and unique.
In fact, it is my deep understanding that we can teach children from 9 years old ahead any single science subject, no matter how advanced. The catch is there is no mass-knowledge about how to do that and therefore we shall rely on self-training of the teacher/instructors alone.
I am also building an "Arduino-kid force" development platform - that is an Arduino nano adapted by myself to the early age teaching methods I experimented. I hope I will complete at least a primitive prototype to show at the Arduno day. I am not quite sure I have sufficient time.
The bus bar is called here "Ground bar" ("bara de nul") or "distribution bar" or "bloc terminal" and cost around 1-2 USD (equivalent) for 8 to 12 poles. I found reference to it in home electric online stores - I will keep posting.
In my opinion is a genial yet simple piece that can simplify the wiring quite a lot. Thaks @pert!
In this age of lawsuits and unreasonably protective parents it is somewhat understandable for people to take the CYA attitude to such lengths but it's really sad because it the loss of opportunities for children to learn and develop is much more harmful than the one in thousands who will get a minor scratch from a sharp lead. I think back to what I was doing with electronics at a much younger age. Of course I didn't have any sort of official educational opportunities. I just dug broken stuff out of a garbage can and dragged it home to tear apart.
WARNING: Failure to securely seat the connector may cause electric shock, short, or start a fire, and lead to serious injury, death, or damage to property.
This is regarding the flat flex cable for the Raspberry Pi camera module, which is running at most 5 V. The fire warning could be reasonable, especially since it's in a cardboard enclosure but putting "electric shock" at the start of a sentence that end with "serious injury, death" is just idiotic. This is intended to be an educational kit. The people using it will be the very ones who have the misconception that every electrical circuit is an electrocution hazard. I don't think causing further confusion actually does anything to improve safety ("I saw someone on YouTube touch the wires on their RPi even though the warning said it could kill you so I guess it's OK for me to poke my finger in the light socket"). And certainly it's going to be more difficult to learn from the kit if you're afraid it's going to kill you the whole time.
Right. For instance, cables can be swallowed or one can self-strangulate by a cable but this should not prevent people to use cables in home appliances. Every single object can be turned into weapon, so what?
I fully agree that learning will occur sooner or later and is much better to control the process than to avoid minor dangers - if any.
There are also kids joking about "getting electrocuted". One told me that it was electrocuted by 3V piles I gave him. I said that he must throw away the smartphone, because it also runs on electric piles as well. . He did not :-).
I also saw an warning about "the danger to put finger in the eye" while taking photos. :-).
Crossing street causes more dead and injuries than anything else. The same with smoking and drinking. But the really serious problem is that this excessive idiotic care prevents proper learning in the case of electricity/electronics.
I am going to stress this problem in the Arduino Day and to write some articles about it. Every little helps.
I am working on this right now. I tried fritzing and it comes to a bunch of crossed wires. So I am going do do it by hand.
In the final project the components are to be mounted like that:
a) Source:- LiIon 18650 ->up/down tp 5V-> 1 common bus bar 5V + 1 common bus bar ground
b) Arduino nano - on mini breadboard
c) Level shifter - on another mini breadboard
d) 3 Sensors - on an Al or PPE U profile (this profile is going to be attached to an exploratory arm)
The display will be mounted on screws+legs to the another U profile.
The controller and the level shifter - by screwing the boards to the U profile.
In this way, the sensors will be separated from the rest in order for the operator to see the values and command the arm.
There is also some mechanic tinkering work on going. I have to connect all parts together:
no soldering, no PCB
clear image of which pin is link to which pin
It has to be solid and functional, in the first place. Maybe I will optimize the construction later on.
I also have two steps ahead in coding:
a) solving out how to show the light values along with other 4 values, on a 2 lines display in a meaningful way
b) optimize the code (no mandatory, if I will have time - that I never have :-)).
From what I found yesterday, the connector's world is of Jupiterian dimension.
The various connector;s names are a matter of inspiration, as far I could see in the hardware stores. Could be some standard names, I do not know - Thank you for any resource - glossary!
In the attached photo you can see the most interesting ones I brought.
a) the "morsettes" - individual 2 ends connectors, linked together in stripes - looks very versatile, like an unidimensional breadboard
b) the bus bars - 2 types: double and simple - heavy but easy to mount by screws
c) the very small: i. 4+1 push-in (permanent) and ii. 4+1 lever-operated - these are impossible to mount - I am planning to tinker them.
The wire nuts I did not find on site, I have to order them on-line.