Smart Circuits: Electronics and Control

You need: An old battery toy, torch or electronic greeting card (batteries removed) · Small screwdrivers · A tray for screws · Safety glasses · Input–process–output sorting mat

1. Check the batteries are out. Put on safety glasses.
2. Before you open it, draw what you think is inside.
3. Unscrew it carefully and lay each part on the tray in order.
4. Find the power supply, the input (button, switch, sensor), anything that processes (a chip or circuit board) and the output (light, motor, speaker).
5. Place each part on the sorting mat under input, process or output.
6. Draw a three-box system diagram for the gadget.

How you'll know: Your system diagram names the real input, process and output parts of the gadget, with arrows showing what flows between them.

Safety: Battery toys only. Never open anything that plugs into the wall, microwaves, or anything with a large capacitor such as a camera flash. Remove any button batteries and hand them to your teacher.

Go further: Find a subsystem inside a subsystem, such as the power supply inside the process block.

You need: 2×AA battery pack · An LED and a 220 Ω resistor · A push button or slide switch · Crocodile clip leads or a breadboard · Circuit symbol cards

1. Connect the battery pack, switch, resistor and LED in one loop.
2. Check the LED's long leg goes towards the positive side. Press the switch.
3. If it does not light, trace the loop with your finger to find the gap.
4. Draw the circuit using standard symbols only, with straight lines and right angles.
5. Swap diagrams with another team. Can they rebuild your circuit from the drawing alone?
6. Now test ten objects (a spoon, a pencil lead, foil, a rubber) in a gap in the circuit and sort them into conductors and insulators.

How you'll know: Another team rebuilds your circuit from your diagram, and it works first time.

Safety: Never connect the battery wires straight to each other; this is a short circuit and gets hot.

Go further: Add a second LED in parallel and a buzzer in series. Predict first, then test.

You need: Resistors: 220 Ω, 1 kΩ, 10 kΩ · A resistor colour code chart · An LED and battery pack · A multimeter (optional)

1. Use the chart to read each resistor's bands. The first two bands are digits, the third is how many zeros.
2. Write the value of each resistor. Check with a multimeter if you have one.
3. Put each resistor in turn in series with the LED.
4. Rate the brightness on a scale you agree as a group, such as 'off, dim, medium, bright'.
5. Make a table: resistance, brightness.
6. Write a sentence that explains the pattern using the words current and resistance.

How you'll know: You can read the value of an unknown resistor from its bands and predict whether an LED will be bright or dim with it.

Go further: Use V = I × R to calculate the current through each resistor with a 3 V supply (ignore the LED for a first estimate).

You need: A micro:bit with battery pack · A device with MakeCode · A torch and a box or cloth to make it dark

1. In MakeCode, make a forever loop that shows the light level as a number.
2. Download it. Cover and uncover the micro:bit's LEDs (they also sense light). Write down the reading in bright light and in the dark.
3. Choose a trigger level between the two readings.
4. Add: if light level is less than your trigger, show all LEDs lit; else clear the screen.
5. Test it ten times by covering and uncovering. Does it flicker near the trigger?
6. Fix the flicker by using two levels: turn on below one number, turn off above a higher one.

How you'll know: Your light turns on in the dark and off in the light every time out of ten, without flickering.

Go further: Add a timer so the light stays on for 30 seconds after it gets dark, then turns off to save the battery.

You need: Two galvanised nails · Two crocodile clip leads · A micro:bit and battery pack · Two pots of soil: one dry, one damp · A cup of water

1. Clip one nail to the 3V pin and the other nail to pin 0.
2. Push the nails into the dry soil about 3 cm apart.
3. Code: forever, show the analog reading from pin 0 as a number.
4. Record the reading in dry soil, then in damp soil, then after adding water.
5. Choose a 'thirsty' level. Code a sad face and a beep when the reading drops below it.
6. Test it over two days in a classroom plant pot and record readings every morning.

How you'll know: Your sensor gives clearly different readings for wet and dry soil, and the alert goes off only when the soil is dry.

Safety: Low voltage only. Wash hands after handling soil. Keep water away from the micro:bit and battery pack.

Go further: Log readings every hour and make a line graph. How fast does soil dry on a sunny day?

You need: A wooden clothes peg · Aluminium foil and tape · A small piece of card · Two micro:bits · Crocodile clip leads · A model trap box (a shoebox with a lid)

1. Wrap foil around the tips of both jaws of the peg. Clip a lead to each foil pad.
2. Slide a piece of card between the jaws. With the card in, the switch is open.
3. Tie the card to the lid of the model trap. When the lid snaps shut, the card pulls out and the foil pads touch.
4. Connect the leads to pin 1 and GND. Code: when pin 1 is pressed, send a radio number (your trap number).
5. On the second micro:bit, code: when a radio number is received, show it and play a sound.
6. Test from across the classroom, then from the other side of the school hall.

How you'll know: The receiver shows the correct trap number every time the model lid closes, and never when it does not.

Go further: Give three model traps different numbers and make the receiver keep a count for each one.

You need: A 9 g micro servo · A micro:bit and battery pack (or a separate battery pack for the servo) · Crocodile clip leads · Card, a skewer and tape

1. Connect the servo: brown or black to GND, red to 3V, orange or yellow to pin 0.
2. Code: servo write pin 0 to 0 degrees, pause, then 90 degrees.
3. Tape a card flag or a model gate arm to the servo horn.
4. Link it to your sensor: when the soil is dry or the trap fires, raise the flag to 90 degrees.
5. Test it 20 times. Does the servo always reach the same angle?
6. Add the servo to your system diagram as part of the output subsystem.

How you'll know: The flag or gate moves to the same position every time your sensor triggers it.

Safety: Keep fingers clear of moving parts. If the micro:bit resets when the servo moves, power the servo from a separate battery pack with a shared GND.

Go further: Replace the servo with a small geared motor and make the EPro8-style flying fox seat move when a call button is pressed, stopping at a limit switch.

You need: Your prototype · A test log sheet with 20 rows · A partner to trigger the system

1. Decide what a true alert, a missed alert and a false alarm look like for your system.
2. Your partner runs 20 trials: some should trigger it, some should not. They keep the plan secret.
3. Record each result in the log.
4. Count the three types. Work out the percentage of correct responses.
5. Change one thing (the trigger level, the switch, a loose wire) and run 20 more trials.
6. Write a sentence comparing the two logs.

How you'll know: Your log shows whether your change made the system more reliable, with numbers to back it up.

Go further: Test in harder conditions: bright sunlight, damp air or a moving table. What breaks first?