I'm sure you've played the "Wire Maze game"...(also called "Sammy the Snake" by shop teachers in our district... ) You thread a wire loop through a maze. A few years ago I built a simple latching circuit that would light (and keep lit) an LED if you touched the wire with the loop. Kids liked it but they were not thrilled by it so I added a ZAPPER in the handle. I also built in a switch so the kids can toggle between a light or a zap.
Now the kids are SO excited i keep this project for last as a reward for doing a good job in the other shops!
I've been teaching electronics for 14 years and i have tried every kind of board making method out there. I used to use the photo-resist method which worked well but became tough to do in large amounts...and expensive! I've also tried the laser-copier paper and the toner transfer paper which work fairly well. The REAL problem is the chemical part of the process. Making a copper board means that the uncovered copper needs to be chemically removed. Big pain. Big mess. Kids in grade 6,7 and 8 with nasty chemicals just sucks.
So enter the method that electronics teachers scorn. Wood, nails and point to point wiring. I scorned this method as hokey and hack until i started using it with my students. THEY LOVE IT!! Hammering and soldering nails with parts attached is just so cool the kids are excited about it. The other advantage is that it is really easy to troubleshoot... problems are obvious! No chemicals, cheap, kids love it and easy to work with. TRY IT!
This instructable is designed as a day to day lesson plan outline for teachers but i think what makes this project excellent also is that you can easily make it at home!
-The students will learn to identify and install basic electronic components including the resistor, SCR, transformer and LED.
-The students will learn about electromagnetic induction and a latch circuit. By understanding these concepts the student will than be able to analyze and troubleshoot the circuit.
-The student will learn to use a soldering iron safely than apply the skills to build a circuit.
-The student will design a game piece than apply the design to build it.
New Vocabulary To research:
Materials: (per student...)
-220R, 1K 1/4watt resistors.
-5mm LED (any color)
-SPDT slide or toggle switch.
-SCR 106B (220 package)
-Transformer MODE 60-282-0 (small green one)
-3 feet of 18-22 Gauge hookup wire. Non stranded...
-30 brass nails... about 5/8" long (or W.H.Y.)
-Block of softwood about 3/4' thick, 3" by 5"
-Solder... i use the 1.2mm rosin core.
-1/16" welding wire (or coat hanger thats been sanded)
-2 small pieces 1/2" by 1" copper clad 1 sided.
-epoxy or double-sided tape.
i find the best place for parts is often DIGIKEY. try them at digikey.ca. They will ship for cheap depending on how much you buy and it is often the next day. VERY FAST. You can also use that old-fashioned device called the telephone and talk to a real live person who is usually very friendly. Heres a few parts numbers to get you started...
-220R resistor is CF14JT220RCT-ND (digikey)
-1K resistor is CF14JT1K00CT-ND (digikey)
-SCR is C106BGOS-ND (digikey)
-transformer is a mode product... electrosonic (http://www.e-sonic.com) has it for $2.50
-copper clad PC94-ND (digikey)
-LED 516-1335-ND (digikey)
-SPDT switch 450-1569-ND (digikey)
There are all sorts of distributors for electronics on the web.. digikey, electrosonic and mouser are all great. Most of the resistors will be a minimum of 10-25 which is still only $3... the switch and transformer are the most expensive at $2.50... pretty cheap!
-Soldering pencil (iron) about 25 watts...
-Drill and 1/16" bit (bigger if you use a coat hanger)
-needle-nose pliers, wire strippers
Submitted by HD Stafford Middle School for the Instructables Sponsorship Program
Step 1: Prepare the Circuit Base
What i do is photocopy the picture 6 times, cut the pictures out, arrange them on a piece of paper than photocopy it 12 times. You'll have enough for 2 classes!
Cut out the wood for the students unless the kids are in woodworking and can do it themselves... You'll need 1 block per student... 1" thick (approx) 3" by 5". Use a softwood that is fairly clear. Knots make hammering tough for the kids. You need to drill a 1/16" hole on each end. Check out the photo.
Cut out the paper nail and wire drawings from above than show the kids how to nail a brass pin into each small circle on the drawing. Some kids have a hard time with this so you could arrange them in pairs. One student can hold the nail with a needle-nose pliers while the other hammers the nail in.
When all of the nails are in, flip the block and gently hammer from the bottom so the nails are all fairly even.
Step 2: Soldering!
The problem is that kids forget that the shiny metal part that is smoking is... well... hot. I know this sounds funny and strange but i've had so many kids touch or even GRAB the hot end. Have kids tie long hair back, remove big coats and wear eye protection. I actually remove kids from the area if they are feeling particularly... um... zippy. Give them a writing assignment until they have a degree of control.
The first and most important part of teaching soldering is to explain that the solder is NOT glue. Kids realize that the solder melts which means that logically it should be poured all over the joint they are working on. This is expensive, wasteful and does not make a good joint. Explain that the metal that needs to be joined must be hot enough to melt the solder without even touching the soldering iron. The purpose of the iron is to heat up the wire and part so that it can melt the solder. The part should be hot enough that the solder flows into the joint. I tell the kids that if they get "pigeon poop" that it is not hot enough... they need to go back and heat up the joint enough that the solder melts in and becomes a volcano shape.
This project is so great for kids who've never soldered because they can try it out with the nails. They can make lots of mistakes, make a big mess, overheat the parts, generally mess up and its okay. it won't hurt the board. (unlike copper clad PCB's... don't even get me started...)
Teach the kids to heat up the nail with the iron and add a little bit of solder. If the part is hot enough the solder will flow onto the nail. Explain that the smoke is from an acid that allows the solder to stick to the metal. Point out as well that HEAT is what makes this work and as extra acid (flux) sticks to the soldering iron tip it stops the heat from getting to the nail. This is where you can pull out the damp paper towel and wipe the tip. It will smoke, which the kids love. This should be done every 3 or 4 joints and always at the end of the day before the shop is cleaned up. The tips will last WAY longer if you do this.
Unleash the students on the nails with soldering irons and solder. I cut the solder into 6" long pieces and stress that it is ALL they will get for the class. This discourages kids from wasting the solder. They love making solder balls. They will need to apply a bit of solder to the end of each nail. This isn't absolutely necessary but helpful and great practice.
Step 3: Adding the Wires
Teach the kids to strip wires. Oh man does this get reactions.
Almost as much as calling files by their technical name. :-)
After they finish giggling about the word "strip" you can move on. I find that while wire strippers are great they tend to get destroyed quickly. I teach kids to use 5" side cutters. They are pretty huge for the purpose but last so much longer. Once kids get the idea that stripping the wire is a balance between just cutting and pulling off the plastic around the wire and not cutting right through they latch on pretty quickly. The occasional kid WILL NOT get it so i keep strippers around to have as an alternative. Make sure that they test the spot where they stripped by wiggling the wire back and forth. This will cause the wire to break if it has been nicked or scored by the cutters at all.
Why strip wires at all is a question I get from time to time with young kids... Take a minute to explain the idea of a conductor and an insulator. After explaining this I ask the kids if they could imagine their house wiring without insulation...
The best way to wire up the board is to get the kids to strip the longest pieces of wires they can. Get them to strip off 1-3" at a time. They start at one end of the line on the diagram and wrap the wire tightly around the first nail. They pull the wire tight, wrap it round the next nail than go on until all the nails on that line are joined. I have so many kids wire across nails that are not joined with a line on the drawing so keep an eye out for them.
A line on the drawing is a piece of wire.
Once all of the nails are wrapped with wire the students can solder the wires onto the nails. Make sure they heat up the nails enough that the solder flows around the whole nail. An incomplete soldering joint is the number one spot where trouble happens.
Step 4: Start Adding Parts
You figure out the value of the resistors by reading the color code printed on it. Look at the colors carefully and you'll see that each resistor has 4 bands of color. One of the bands is a bit separated from the others. It should be a gold color. Some resistors have other colors but gold is the most common. Hold the resistor so that the gold band is closest to your right hand. I write the words "GOLD BAND RIGHT HAND" on the board to remind the kids. If you hold it the other way its like reading a book upside down. confusing.
Now read off the colors. The colors all represent numbers. The first 2 colors are written down just as you see them in any resistor color chart. Here is a link..
its kind of cheating but that's okay.
220R... the first 2 colors are red/red. red is 2 so the first 2 numbers are 22.
1K (or 1000R)... the first 2 colors are brown/black. Brown is 1 and black is 0 so the first 2 numbers are 10.
The third band is how many zeros are at the end of the first 2 numbers.
220R... the third band of color is brown. Brown is 1 so you add 1 zero to 22. This gives you 220.
1K ... the third band of color is red. Red is 2 so you add 2 zeros to the end of 10. This gives you 1000.
I've used a precision resistor that i had sitting around and it is blue...don't worry about it... You don't have to use one...
1000 is shortened to 1K. Explain that the 3 zeros are replaced by a K. I explain this idea by telling and writing on the board the value of 100000 M/Hr and say that i drive on the freeway at this speed. Is it true? Sure it is. Just cross out 3 of the zeros and replace them with a K and you have 100KM/Hr. This might not be quite so effective if you use Miles/Hr :-)
Now solder on the resistors where they are labelled on the diagram. I get the kids to just lay the wires on the nails, heat them up and solder them on. Some kids find it easier to wrap the wires first. Be sure to trim off any extra wires sticking out! Also be sure that the wires under the resistors don't touch the resistor wires.
Step 5: Adding the SCR and Switch
Check out the drawing above. When you switch the toggle switch towards the SCR it provides a negative to the SCR. The middle pin of the SCR is attached to a resistor and LED... the other side of which goes to positive. Normally the SCR stops the electricity from flowing through the LED but when you apply a bit of power to terminal 3 of the SCR the power will flow through and the LED will light. But here's whats cool about the SCR... it will stay that way until you re-set the SCR. We do this by taking the negative away from pin 1 of the SCR temporarily by switching the toggle back and forth.
I tell the kids about SCR's by explaining the idea of a gate with a latch... if the gate closes far enough it will stay that way... Just a small push can stop a snarling crazy dog... thankfully...
The SCR is pretty tough but you can't let it get too hot. What i suggest to the kids is that when they solder they do one lead, wait a minute or two than move to the next lead. They should be able to touch the body of the SCR without burning their fingers.
Solder the SCR to the spot on the board. Look at the drawing and picture to give you an idea of how it all goes together. Make sure that the SCR is facing the right way... it has POLARITY...
You can solder on the switch now. Most switches are too small and the leads need to be stretched to the nails. This seems to work well. The other option is to use a bigger switch or move the nails closer together. I would not suggest moving the nails closer together because kids have a tough time hammering them in to place.
The purpose of the switch is to allow the user to choose between playing the game with the LED going on or the ZAPPER going on. All it is doing is moving the negative (black wire) from the battery from LED to ZAP. When you move the switch towards the LED it chooses that part of the circuit and the opposite for ZAP.
The switch can be fairly expensive and kids love to play with it.. i might suggest that you hand them out carefully... one by one... Don't forget to make sure that the metal case of the switch doesn't bridge the gap between the nails.
Step 6: Adding the LED and Power Leads
I find it easiest to prep the LED wires first by heating them a bit than adding solder... kids find this easier because the LED wires can be a bit fiddly. If you prep them first they are quicker to solder. Make sure the NEGATIVE lead is UP. The LED also does not like getting too hot.
Add a link where shown or you can add a reset switch which is just a NC (normally closed) push switch. We don't have much money in our school district so i opted to not use it... you can use the slide switch as a reset too... it just isn't as fancy.
Solder on the Power Leads from the 9 volt battery snap. The red wire goes towards the link and the black wire goes on the other nail. Its on the drawing...
Step 7: Testing the LED and SCR
I've been adding steps as they usually happen in the class... Sometimes kids are faster and sometimes slower. Its okay to have the kids at different places but i would suggest that before you get to this point it's a good idea to have the kids at the same spot... ready to test.
Attach the battery, move the switch towards the LED and solder a lead about 2" long to the positive side of the battery attached to the circuit... somewhere near the red wire. Touch either side of the link with the wire lead and the LED should go on than stay on. It will turn off if you move the slide switch back and forth. If the LED does not go on here are some spots to check:
-The 220R resistor sometimes gets mixed up. If its too high of a value the LED won't light up.
-Make sure the LED is on correctly... polarity wise. Same deal with the SCR...
-Kids sometimes get huge blobs of solder that bridges the switch leads. Clean a soldering iron and swipe in between the nails.
-Is the jumper there? if not, is it a NC switch? (they usually have black buttons...) if you're unsure about the switch install a jumper across the NC push switch and see if it solves the problem.
-Go over all of the solder points and make sure that the joints are all perfect. Cold solder joints are a real pain... they LOOK good but are not actually electronically joining the parts. You can fix this by re-heating suspect spot, adding solder and letting it cool.
-Make sure all of the wire bridges are there. Kids forget! (come to that... so do I... )
It seems like a long time to spend on one part of the project but what I've found is that you can use the time to make sure all the kids are caught up and the circuits are all working. Trouble-shooting takes a really long time.
Step 8: Whats in a ZAP?
I start by writing ELECTROMAGNETIC INDUCTION on the board. I ask the kids how many volts the battery is putting out. (9v) Than i ask how many volts are coming out of the wall. Kids usually have an idea.. here in Canada its 120V AC. I prompt the kids to guess the voltage produced by the transformer using electromagnetic induction... whats awesome is that they never imagine that it is taking 9 volts and turning it into more than 400. So why don't the kids get knocked out by the huge voltage? Why is 120v coming from the wall deadly? At this point I ask them how many volts is static electricity? They NEVER guess that its 25000 or more.
so why is it that on a dry static filled day that we don't walk around... shuffle our feet on the carpet... sneak up behind a friend and touch them on the back of the arm resulting in a HORRIBLE SHOCKING of a friend??!! I always act out the whole scene... shuffling... reaching out... the CRACK of electricity... Collapsing on the ground in a heap...Kids love it.
This is a perfect time to explain what makes up electrical POWER... You have to have VOLTAGE (which they've figured out) AND you have to have AMPERAGE. I find that a good way to explain this is that voltage is how hard the push is and amperage is how much of it is there. I've seen all sorts of great ways of explaining power... a closed tube with a pump and a meter to show power is good... just change the size of the pump (voltage) and the amount of water (amperage). A HUGE pump with just a tiny bit of water explains the zapper and static shocks. Check out the web for hundreds more. remember to keep it simple. I've explained this to ADULTS before who could not figure it out... let alone a kid in grade 7...
kids usually get it faster.
Now explain Electromagnetic Induction.... Its a simple but bizarre thing. The idea is that if you got a wire and pulsed electricity through it, a magnetic charge would happen around the wire. If you want, you can quickly whip up a nail magnet by wrapping wire around a nail. When you apply power to the wire it turns the nail into a magnet.
Most kids get this already.
But here's the weird thing. If you hold another wire with a sensitive voltmeter attached to it close to the wire with pulsing power on it the meter will show a voltage going through the wire. The collapsing magnetic field INDUCES a charge through the other wire. By changing the length of wire and wrapping it around a form of some kind you can change the amount of electricity that is produced.
What happens in a transformer essentially is that in the transformer you have 2 windings of wire. One has a pulsing voltage going though it. The pulsing voltage produces a magnetic field that opens and closes over the other winding. When this happens an electrical charge flows through the other winding. You can mess around with the amount of wire in the windings to make different voltages... We're using the transformer to change 9volts into 400 (give or take...)
Remember to explain that the voltage is going UP but the amperage is going DOWN which explains why this circuit will shock you but not too badly.
This might take a whole class but if you have time left move on to the next step.
Step 9: Install the Transformer
Now the kids need to make the probes. What i do is teach them to solder wire to the copper pads by first heating up the pads and applying solder. I than strip the long wires on both ends and prep one end of them by heating and applying solder on to the wire. Prepping both the wire and the copper pad makes it easy to solder the 2 together.
I use 1/16" welding wire for the probe. You can use really any wire that you have around but make sure it can be soldered!
The welding wire has a coating that allows it to be easily soldered.
Cut the wire to about 6" long than help the kids form a loop on one end. Some kids find this really tricky. Solder prep the end without a loop than solder it to the copper board. Check out the photos for clarification. It's important to solder the copper pad with the probe to the lower nail... remember it is a switch... it allows you to apply a positive voltage to either the ZAP or the SCR.
Don't forget the piece of wire that will join the board to the maze. You can solder it to the circuit now if you want.
Kids always want to test it at this point. Use a piece of double-sided tape or some epoxy to attach the fiberglass sides of the copper board together... Make sure kids don't glue the copper sides together. Don't laugh, it happens!
expect the unexpected i say.
Step 10: Make the Maze
I explain the idea of threading the loop from one end to the other without touching. Ask for ideas... let kids come up and draw on the board, it really gives them confidence and it empowers them to try! Get lots of ideas... remember no idea is "wrong"! you can take ideas that seem crazy and make them work.
What i do now is ask the kids to fold a piece of paper into 4 sections. They use both sides of the paper so what they have to do is come up with 8 ideas of a maze for their project and draw it in each section. I get them to do the folds so they will have to fill the area with the drawing. It also HAS to be completely different in each section. Don't let them get stuck on one idea.
Once they have ideas, ask them to focus on one but now apply the guidelines...
-It has to fit into each end of the base. Show them a base where the holes are drilled.
-It has to use a certain amount of welding wire... this depends on what you have but 2-3 feet is lots.
-It has to be DO able... it has to be useable. If it is too tricky no-one will try it. Avoid loops. Its almost impossible to play the game with a loop in it.
Once they have a drawing or two with the guidelines in place get them to draw the base in scale with the wire maze drawn in place. I show them how to use a piece of string laid on the drawing to figure out how long of piece of wire they will need. Once they have laid the string down they need to straighten than measure it. I won't give them a piece of wire unless they tell me EXACTLY how much they need.
Once the students get the wire they can bend it into shape than stuff it into the ends of the block. a bit of epoxy will hold it in place. Solder the wire from the maze to the board. When the kids touch the loop to the maze they are closing a switch that applies a positive to either the SCR or the zapper depending on which way the switch is.
Step 11: A Marking Sheet
I use a similar marking sheet for all of my projects. I like to show it to the kids first... maybe tape it to the wall. The kids can look at it and understand what a grade looks like. If they want an "A" they will know what to do to get an "A". I think this is fair because kids should NOT be surprised by the mark they get! If a kid does get a low mark i always give them an opportunity to go back, revise, fix, repair... whatever they need to do to get the mark they think is fair. I like to keep in mind that a project (or TEST for that matter) is all about allowing a kid to show what they can do... not what they can't do.
here's the sheet!
Wire Maze Marking Sheet
NAME:___________________________DIV:______ Grade of possible /60
Lots of messy joints, some not there, Loose wire soldering
All soldering done But still lots of blobs and cold joints
Perfect. Shiny joints, smooth soldering, strong
Wires And Parts
Some wires missing.
Parts in wrong or missing
Everything there but parts sticking up all over, wires not tight
Parts in straight and tidy, Wires in tight and straight, wires to probes same length
Both functions not working. (LED and ZAP)
One function only working, other not consistant.
Both working perfectly and consistently.