THE LADDER

EVERY PROJECT ON THE LADDER

LEVEL 1 · FIRST LIGHT 21 in 1

Batteries, resistors, LEDs and the loop that joins them.

• № 1 Light the LED — Press the button and the red LED lights. Let go and it goes dark.
• № 2 Dim it with the pot — Turn the knob and the LED goes from bright to almost out.
• № 3 Two-transistor flasher — The red and green LEDs take turns blinking, about once a second.
• № 4 Make a tone — Turn the speaker on and hear a steady tone around 700 Hz.
• № 5 Light-controlled tone — Drag the light slider under the CdS cell (or turn on the camera and cover it) and the pitch changes.

LEVEL 2 · TIMING & CONTROL 32 in 1

Series and parallel, a transistor as a switch, and capacitors that set the pace.

• № 6 Series LEDs — Both LEDs glow, and each is dimmer than the red one was alone through the same 1 kΩ.
• № 7 Parallel LEDs — Both LEDs at full brightness at once, each on its own 330 Ω.
• № 8 A knob that carries no load — Turn the pot and the LED dims, but the pot itself only ever handles microamps.
• № 9 Slow on, slow off — Hold the button: the LED fades up over a couple of seconds. Let go: it stays lit and fades out slowly.
• № 10 Siren knob — Turn the speaker on and turn the new pot: the pitch slides from a low buzz up to the tone of experiment 4.

LEVEL 3 · SOUND & SENSE 44 in 1

Stack batteries, store charge, and turn light and knobs into sound.

• № 11 Twice the push — With two batteries in series the LED through 1 kΩ is about twice as bright as with one.
• № 12 Capacitor battery — Hold the button to charge the 470 µF, let go, and the LED keeps glowing for about half a second as the capacitor empties.
• № 13 Metronome — Turn the speaker on and hear a steady click about three times a second.
• № 14 Two-tone — Turn the speaker on: the slide switch flips the tone between two pitches.
• № 15 Light theremin — Turn the speaker on. The light slider plays the pitch, and the new pot tunes it: each sets one half of every cycle.

LEVEL 4 · RELAY LOGIC 64 in 1

An electromagnet that throws a switch: NOT, memory, an alarm, and the bell.

• № 16 One coil, two circuits — Green is lit at rest. Hold the button: a click, green goes out and red comes on. Let go: click, back to green.
• № 17 Kickback — Hold the button: click, LED on. Let go: click, LED off, and Q1 is still alive. Now pull the diode's wires and try again: Q1 dies the moment you let go.
• № 18 Dark alarm — Slide the light toward the moon: click, and the buzzer sounds. Back toward the sun: click, silence.
• № 19 The relay that remembers — Slide ON. Tap the button: click, LED on, and it stays on after you let go. Slide OFF: click, LED out. Slide ON again: still off until you tap.
• № 20 The electric bell — Turn the speaker on and slide ON: a low buzz, around 90 Hz, and the relay blade shivers.

LEVEL 5 · LOGIC LANE 102 in 1

A chip that keeps time, gates that decide, and a digit the room can read.

• № 21 The pad beacon — The red lamp blinks on its own, about two thirds of a second on and two thirds off, and nothing you do to the board changes it.
• № 22 Range safety — Turn the speaker on: a tone. Turn the knob and the pitch climbs from a low hum near 690 Hz to a shriek past 3 kHz.
• № 23 Go / No-Go — Slide ON and hold the button: the lamp lights. Either one alone: nothing. That is AND.
• № 24 Set the digit — Nothing pressed: 0. Button: 1. Slide: 2. Both: 3.
• № 25 Zero — Hold the button and the clock sits at 9. Let go: 9, 8, 7, all the way to 0, about one step a second, with the lamp ticking. Then it rolls round to 9 and starts again.

LEVEL 6 · POWER 107 in 1

What is inside a cell: side by side, mismatched, backwards, shorted, and sagging under load.

• № 26 Two in parallel — Two batteries side by side give the LED exactly the brightness one did, and each carries half the current, so the pair lasts twice as long.
• № 27 The mismatched pair — A 9 V block and a 1.5 V cell side by side both read HOT at once, and the block is flat in about ten seconds.
• № 28 One cell backwards — Three cells in a row make 4.5 volts and the buzzer sounds. Turn the middle one round and the stack makes 1.5, and it goes quiet.
• № 29 The dead short — One wire from + to −: about five amps, HOT at once, and the gauge on the case empties in about ten seconds.
• № 30 Load and sag — Switch off, the battery reads 9.00 volts. Switch on, it reads 8.89 — and for an instant on the way there it reads nearly a volt lower still.