This is the text I supply as a starting point for setting up electronics in a school situation, but equally it applies to hobbyists and youth groups. Its what you need to know to get started…
Electronics for Design Technology.
The trouble with electronics is that everything has to be right for things to work and unlike a close fitting mortise and tenon joint, you cant actually see what is going on. When I first started teaching, I embarked on my first class of circuits with some trepidation, fearing hours of fault-finding long after the pupils had gone home. Happily this was not the case and after this course I hope you will feel the same way. Having working examples to refer too does great things for your confidence, even if initially you are fixing by comparison. Your knowledge base rapidly expands!
First off, a bit about what you need for a set-up to begin this sort of work and then away we go.
Our first explorations are going to be based around the LED, just over 50 years old now, and the 555 timer chip (Integrated circuit or IC) which was first introduced in 1971 and is still freely available even now, 41 years later, testament to its flexibility and ruggedness. Of course there is a Wikipedia page all about it here: http://en.wikipedia.org/wiki/555_timer_IC The clever chap who designed it passed away recently, but he certainly left his mark.
If you are desperate to try a circuit, you can try how twas done in olden days by using point to point wiring on a scrap piece of wood. Early valve radios were often built around a tag strip, you can even build circuits ugly style with the chips upside down and components hanging in thin air. Its not recommended though and thankfully printed circuit boards came along later, making assembly of more than one or two components a lot simpler.
Although we are NOT going to try this building method, circuits of this sort of complexity are not to be recommended unless you have no option or enjoy electronic art. Fault finding in particular can be hard going, even if you built it yourself. If its someone elses work, yikes! YOU JUST DONT WANT TO GO THERE!
Now lets introduce printed circuit boards the way to survive electronics!
Time was every DT department had an etch tank, nowadays due to cost, staff availability and probably concerns over H&S they are a relative rarity. Disposal of the etchant chemicals needs reference to your local authority too and possible attendant costs. Fortunately, lots of small suppliers in the UK offer a whole range of ready to go kits and they are pretty much 100% pcb based.
PCBs reduce the electronics to an assembly task, but if it facilitates functionality, then just as buying a door hinge allows you to hinge a door (rather than making the hinge itself) then why not? At the end of the day not everyone wants to understand everything about everything, but a few will and those will be the ones asking the …so how does that work type questions, at which point they are directed to the extension material (and listed on your G&T register).
Some suppliers may offer a scheme whereby they piggyback your pcb design(s) onto their orders and that way you benefit from the cost savings of a product usually made in China. Small will be cheaper so its worth optimising your design for minimum space requirements. I have always tried to minimise waste and like to think that my boards are relatively pupil-proof but equally compact. Software like Crocodile Clips does do PCB layout for you at a basic level, but you may find running costs a bit high and although the software simulates circuit action, as every circuit is different its just as bad as trying to untangle a rats nest.
The PCB designs used by us today were designed by me using Designspark (Industry standard FREE software from RS components for drawing circuit diagrams and PCBs). There are educational packages that take on-screen circuits straight into a pcb (Circuit Wizard seems popular), but they are rarely optimised for layout or size. After 40 years of designing PCBs (from painting on nail varnish through to photo-etch methods and now commercially) I always try and (a) make them compact and (b) pupil proof ….. to a degree if something does not easily fit it is probably in the wrong place! Soldering skills, or the lack of them, will probably be the main cause of grief for you whatever method you use.
Introduction setting up for soldering circuits successfully:
Examination boards used to issue marking guidelines to schools that suggested soldering is a low-level skill and is not worthy of credit in project work. True maybe, but without good soldering your project will not work, or if it does, will only work sometimes and be plagued by unreliability. Spend some time on teaching it my way and you cant go wrong, although certain pupils will no doubt find a way….
What sort of tools?
For pupils: Antex CS18, 2.3 mm tip, mains powered with silicon lead, stand and sponge. You might want to fit the stand onto a larger MDF base for stability and maybe provide a recess for the solder pot. Always wet the sponge. On first use and power-up, immediately tin the iron tip as it warms up or it will become forever useless! If you ever replace the tip, do the same thing. Specialist tip restorer is available from Rapid Electronics, part number 50-4056. If you have a buoyant budget, try and buy a temperature controlled iron such as the Antex TCS 85-0550, but at £40 + vat each 10 off its expensive.
For you: A GOOD 50 watt temperature controlled unit (like the Antex one above) or browse Rapid, CPC, Farnell or ebay for the cheaper Chinese Adjustable on a stand units. If you have funds a Weller TCP type and matching base/power supply is the Rolls Royce. You may well find a solder sucker useful, although not essential it can be handy. Buy from RS components, p/n 479-4197 and at the same time some spare nozzles p/n 479-4204. It is the only one in the world worth buying, not the cheapest, but definitely the best! DO NOT let the pupils have access to this tool. A small roll of de-soldering braid can be useful too Ill show you this miracle material. Another one NOT to let into the hands of the pupils!
Solder: Use the Tin/Lead stuff there is no legislation about it that applies to schools and it is just so much better. Now wash your hands please needs adding to your SOWs though as lead is harmful when wilfully ingested.
I am hoping to have a video of How to Solder, but there are numerous Youtube videos etc.
Soldering guide here: http://www.antex.co.uk/pages/paper3.htm
Buy the cheap blue-handled side cutters from Rapid Electronics (p/n 85-0205) and the same number of long-nosed pliers (p/n 85-0225). I do not recommend wire strippers and I will show you why and how to do without them. I have yet to find one that is genuinely good, but its up to you.
Solder pots ask your friendly photo-processing shop/chemist to save the 35 mm film pots stock up while you can, 35 mm film is fast approaching historical status!
Soldering irons operate best at between 370 and 400 degrees Centigrade they will burn you, your clothes, desks etc. PLEASE take care, the burns are deep and painful…run the affected part under cold water until the noise stops!
NOTE!! My school recently installed a voltage optimiser, taking the mains voltage down from a healthy 243 to a miserable 219. Net result, most of the soldering irons dont quite get hot enough, unless they are temperature controlled types. Worth checking before you spend the money. A cheap Rapid Electronics unit does work OK, but Im unsure about the long term quality unlike the Antex irons which are in many cases over 10 years old!
OK, Im bored with talk, can I build something? Nearly, but not quite. We will need some sort of power supply to power our various circuits and although batteries are fine, they can soon become a significant cost.
Sustainability, re-use, re-purposing, recycling, up-cycling, whatever you want to call it is a good thing. Its even on the GCSE syllabuses (so it must be good). We will now re-purpose a surplus mobile phone charger. The vast majority of phone re-cycling companies do not want the charger. This means that a huge number of these handy devices languish in the drawers and cupboards of staff and pupils. A verbal request or a note on the termly Headteachers newsletter usually nets a useful quantity. They can generally be used for nearly all project work. They are especially useful to have around the lab/workshop as batteries and cells seem to vanish.
The heavy units are not as handy as the lighter switched mode types, easily distinguished by looking at the input voltage range. If it says input 100-240 vac, output 5v, 500mA or 800 mA then great. Next step, check it REALLY IS SURPLUS as we will cut the phone end plug off and strip the wires. With a digital multi-meter set to 20 volts identify the +ve (positive) lead and 0v (negative). The colour code cant be trusted. Strip a short length of the insulation and tin the wires. Apply heat-shrink tubing to the two wires of a PP3 battery snap, and some larger heat shrink to the actual phone charger cable. Solder up the wires backwards i.e. black snap wire to +ve, red snap wire to ve. This is because the battery snap is polarised and will, from now on, pretend that it is a battery pack. Shrink the tubing to provide a neat and well insulated joint.
Test the battery snap for polarity the small round one should be +V.
You have just saved something that will ‘come in useful one day’ from the e-waste pile!