Lesson #17: Brushbot

This robot as a BIG version of the tiny Bristlebot robot. Using an eccentric drive motor, this robot will show you how a cell phone vibrates by using an off-center weight being slung around by a motor.

We built these types of robots in all sizes: from tiny toothbrush versions all the way to large commercial-sized sweeper brooms. This project is just the right size to give you a fun robot that really works. It's lightweight enough so you don't have to use large, expensive motors or power supplies and worry about high voltage... so enjoy!

Materials:

• old brush
• 3V DC motor
• 9V battery
• two alligator clip wires
• wood clothespin
• hot glue gun

Lesson #18: Superfast Bug Bot

This project is advanced students. If you like tiny robots, then this one is for you! Powered by cheap hobby motors, this fast little robot zips 'round and avoids obstacles using momentary switches and an idler wheel for a tail.

I recommend watching the entire video first, then rewind and watch again, this time building as you go. Make sure you have all your parts laid out ahead of time, or you'll get frustrated partway through if you have to stop. You will need a soldering iron to make this project.

You will need to find:

• 1 large paper clip
• 1 round bead that fits onto the large paperclip
• 2 small paperclips
• Insulated wire (you can also use the wire from your battery holder, as you'll have to snip most of it off anyway)
• Soda can (empty and clean)
• AA battery holder with AA's
• 2 momentary switches
• 2 hobby motors (with gear attached if you can find them)
• 2 3/16" female "quick disconnect" connectors
• Heat shrink tubing
• Optional: slide switch

Tools:

• Wire strippers
• Pliers
• Soldering iron, solder, stand

Lesson #19: Trip Wire Alarm

Burglar alarms not only protect your stuff, they put the intruder into a panic while they attempt to disarm the triggered noisemaker.  Our burglar alarms are basically switches which utilize the circuitry from Basic Circuits and clever tricks in conductivity.

The trip wire is an NC (normally closed) switch, meaning that this circuit works until you trigger the switch. So we need a way to stop the current (flow of electrons) until we want the buzzer to activate.

When you stick the paper index card between the two tacks in the clothespin, it breaks the electrical connection and the switch goes in the OFF position.  Remove the paper and your switch moves to the ON position, and electrons are flowing around and around your circuit, and you hear a BUZZZZZZZZZ! This alarm has a thin wire that someone "trips", which pulls out the card, closes the switch, and sounds a buzzer or lights up an LED!

Here's what you need:

• AA battery case
• 2 AA batteries
• 3 alligator clip wires
• wood clothespin
• 4-6" piece of steel or (uninsulated) copper wire
• 2 tacks
• buzzer or LED

Download Student Worksheet & Exercises

Troubleshooting: Installation Tip: Hide this switch down low by the door frame and use fishing line instead of string to make this burglar alarm virtually invisible.  Use a tack in the frame or tie the line to the door hinge to secure and wait for the action...

Exercises

1.  How does this work?
2.  What type of switch is the trip wire?
3.  Name three places you can install this alarm.

Lesson #20: Pressure Sensor Burglar Alarm

By controlling how and when a circuit is triggered, you can easily turn a simple circuit into a burglar alarm – something that alerts you when something happens. By sensing light, movement, weight, liquids, even electric fields, you can trigger LEDs to light and buzzers to sound. Your room will never be the same.

Switches control the flow of electricity through a circuit. There are different kinds of switches. NC (normally closed) switches keep the current flowing until you engage the switch. The SPST and DPDT switches are NO (normally open) switches.

The pressure sensor we’re building is small, and it requires a fair amount of pressure to activate. Pressure is force (like weight) over a given area (like a footprint). If you weighed 200 pounds, and your footprint averaged 10” long and 2” wide, you’d exert about 5 psi (pounds per square inch) per foot.

However, if you walked around on stilts indeed of feet, and the ‘footprint’ of each stilt averaged 1” on each side, you’d now exert 100 psi per foot. Why such a difference?

The secret is in the area of the footprint. In our example, your foot is about 20 square inches, but the area of each stilt was only 1 square inch. Since you haven’t changed your weight, you’re still pushing down with 200 pounds, only in the second case, you’re pressing the same weight into a much smaller spot… and hence the pressure applied to the smaller area shoots up by a factor of 20.

So how do we use pressure in this experiment? When you squeeze the foam, the light bulb lights up! It’s ideal for under a doormat or carpet rug where lots of weight will trigger it.

Here's what you need:

• thin sponge or foam square (about 1" square)
• AA battery case
• 2 AA batteries
• 3 alligator clip wires
• 2 large paper clips
• scissors
• aluminum foil
• buzzer or LED

Download Student Worksheet & Exercises

Troubleshooting: There are a few problem areas to watch out for when building this sensor. First, make sure the hole in your foam is big enough to stick a finger (or thumb) easily through. The foam keeps the foil apart until stepped on, then it squishes together to allow the foil to make contact through the hole.

The second potential problem is if the switch doesn’t turn the buzzer off. If this happens, it means you’re bypassing the switch entirely and keeping the circuit in the constant ON position. Check the two foil squares - are they touching around the outside edges? Lastly, make sure your foam is the kind that pops back into shape when released. (Thin sponges can work in a pinch.)

What’s happening? You’ve made a switch, only this one is triggered by squeezing it. If you’re using the special black foam without the hole, it works because the foam conducts more electricity when squished together, and less when it’s at the normal shape.

First, the special black foam is conducting some (but not enough) electricity when you squeeze it. It’s just the nature of the black foam included with the materials kit. Second, when you squeeze it, you’re getting the two foil squares to touch through the hole, and this is what really does it for your LED. When you release it, the foil spreads apart again because they are on opposite sides of the foam square.

Bonus Idea: Stick just the sensor under a rug and run longer wires from the sensor to your room. When someone comes down the hallway, they’ll trigger the sensor and alert you before they get there!

Exercises

1. How does this sensor work?
2. What makes this an NO switch?
3.  How can you use both the trip wire and the pressure sensor in the same circuit? Draw it out here:

Lesson #21: Remote Controls I

Radio control (RC) is a 100 year-old technology. RC requires both a transmitter and a receiver. The control box sends commands to the robot the same way you change channels on the TV with the remote.

The difference between RC (radio control) and IR (infrared control) is in the frequency of the signals. With the radio controller, the light waves that carry the command information are lower energy, lower frequency signals. The TV remote uses higher energy, higher frequency infrared signals called CIR (consumer infrared).

Both RC and CIR require circuit design at a college graduate level. However, wired remote controls are well within the reach of any young budding scientist.

By simply removing both the battery pack and switch assembly from the robot, stuffing them in a box, and extending the wires from the box to the robot, you’ve got a wired remote control and a lightweight (and usually faster-moving) robot.

Simple remote controls are a great addition for both the water bot and race cars. Once the kids build the robot and they’ve gotten over the initial “WOW!” factor, they’ll probably wonder how to turn it off so they can work on it further.

This is an excellent place for a question… “How are you going to turn the motor on and off easily?”

Use the simple SPST switch for these two robots and use 10’ long wires (flexible one-line (2-wire) telephone cable works well).

Materials:

• your robot that you want to control (use any from this section)
• index card
• 2 brass fasteners
• 1 paper clip
• 2 additional alligator clip lead wires
• optional: plastic soap container
• optional: drill with drill bits

Lesson #22: Remote Controls II

If you've made the water bot, you can use this wired remove to make the motor turn both forward and reverse. All you need is an extra set of wires (telephone cable with two wires in it work great, or else twist two long wires together... they can be as long as you want.) Enclose the whole thing in a plastic box (I like to use tupperware or a soap box) and drill three holes in the top for the brass fasteners and one in the side for the wire and you're all set!

Materials:

• your robot that you want to control (use any from this section)
• index card
• 3 brass fasteners
• 1 paper clip
• 4 additional alligator clip lead wires
• optional: plastic soap container
• optional: drill with drill bits

Lesson #23: Latching Circuit

Once you've made the Pressure Sensor burglar alarm, you might be wondering how to make the alarm stay on after it has been triggered, the way the Trip Wire Sensor does. The reason this isn't as simple as it seems is that the trip wire is a normally closed (NC) switch while the pressure sensor is a normally open (NO) switch. This means that the trip wire is designed to allow current to flow through the tacks when there's no paper insulating them, while the pressure sensor stops current flowing in it's un-squished state. It's just the nature of the two different types of switches. However, we can build a circuit using a relay which will 'latch on' when activated and remain on until you reset the system (by cutting off the power). This super-cool latching circuit video will show you everything you need to know.

Materials:

• relay (from Unit 11)
• your completed Pressure Sensor circuit
• SPST switch (optional)

Download Student Worksheet & Exercises

Use 9V for your batteries, the first switch is SPST, the second is the pressure sensor, the B stands for 'buzzer'. The spring-looking thing is the relay coil, and the contacts are the three lines above the circuit hooked on either side of the second switch. Watch the video for real-time step-by-step instructions on how to build this!

Exercises

1.  What is a relay?
2.  What does the relay do in this circuit?
3.  Draw out a picture that shows how everything is connected in your circuit:

Lesson #24: Electronic Static Charge Alien Detector

This simple FET circuit is really an electronic version of the electroscope. This "Alien Detector" is a super-sensitive static charge detector made from a few electronics parts. I originally made a few of these and placed them in soap boxes and nailed the lids shut and asked kids how they worked. (I did place a on/off switch poking through the box along with the LED so they would have 'some' control over the experiment.)

This detector is so sensitive that you can go around your house and find pockets of static charge... even from your own footprints!

You will need to get:

• 9V battery clip (and a 9V battery)
• MPF 102  (buy 2 - one for back up)
• LED (any regular LED works fine)

Download Student Worksheet & Exercises

After you've made your charge detector, turn it on and comb your hair, holding the charge detector near your head and then the comb. You'll notice that the comb makes the LED turn off, and your head (in certain spots) makes the LED go on. So it's a positive charge static detector... this is important, because now you know when the LED is off, the space you're detecting is negatively charged, and when it's lit up, you're in a pocket of positively charged particles. How far from the comb does your detector need to be to detect the charge? Does it matter how humid it is?

You can take your detector outdoors, away from any standing objects like trees, buildings, and people, and hold it high in the air. What does the LED look like? What happens when you lower the detector closer to the ground? Raise it back up again to get a second reading... did you find that the earth is negative, and the sky is more positive?

You can increase the antenna sensitivity by dangling an extra wire (like an alligator clip lead) to the end of the antenna. Because thunderstorms are moving electrical charges around (negative charges downwards and positive charges upwards), the earth is electrified negatively everywhere. During a thunderstorm, the friction caused by the moving water molecules is what causes lightning to strike! (But don't test your ideas outside in the wide open while lightening is striking!)

Exercises

1. When the LED is on, what do you think it means?
2. Does the LED turning off detect anything?
3. Do aliens like humidity?
4. How does this alien detector really work?

Lesson #25: More Sensors

If you want your robot to detect when it's flipped sideways, this is the sensor you need. It's ridiculously simple to make, and works great as long as the metal makes good contact. I've also included instructions for making a motion sensor as well, just in case you need to detect motion or acceleration.

Materials for the Tilt Sensor:

• film canister
• 2 AA batteries
• AA battery case
• aluminum foil
• buzzer or LED
• alligator clip wires
• small paper clips
• scissors

Materials for the Motion Sensor:

• wire coat hanger (sandpaper might be needed if your coat hanger is coated with enamel)
• ball chain
• film canister
• vice grips
• 2 AA batteries
• AA case
• alligator clip wires
• LED
• scissors
• tape

Lesson #26:Batteries

Before you reach for the pack of Duracells, watch our video on the best batteries to use when starting out with your electricity experiments. (The answer is much cheaper than you think.)
Here's what you need to know:

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