Timing & Control

What you should see

The lamp stays dark for thirty seconds while the 470 µF fills to 9 V. Press the button and it flashes once and is gone.

Parts

9 V battery, 10 kΩ resistor, 470 µF capacitor from the drawer, pushbutton, lamp from the drawer

How it works

Nine volts through 10 kΩ into 470 µF fills in steps of about 4.7 seconds: 1.7 V after one second, 7.9 after ten, 9.0 after thirty, and so little current gets past that resistor that the lamp never lights. Press the button and the capacitor is straight across the lamp with nothing in the way — the brightness peaks fifteen milliseconds later and is over in about thirty. The 470 µF at 9 V holds 0.019 joules, and the whole trick is spending it in thirty milliseconds instead of thirty seconds.

Wiring

1. 1 → 11
2. 12 → 46
3. 47 → 2
4. 46 → 38
5. 39 → 48
6. 49 → 2

Open it on the bench: ohmsville.com/bench#a=stored-then-spent

Learn more: Classroom, Capacitors and time, paragraph 1 — ohmsville.com/classroom#capacitors-and-time-1

What you should see

Sit on it — hold the button — and it blows a raspberry. The knob hidden under the same cushion is how rude: 135 Hz at one end of it, 683 Hz at the other. Stand up and it stops dead.

Parts

9 V battery, pushbutton, 2 × 330 Ω, 2 × 10 kΩ, 2 × 0.1 µF, Q1, Q2, speaker, 100 kΩ pot from the drawer

How it works

A switch in the supply rail gates the whole circuit rather than one path through it: with the button up there is no nine volts anywhere and the speaker reads nothing at all. Held, the two transistors take turns as fast as the two 0.1 µF capacitors can refill through their base resistors, and the 100 kΩ pot is in series with one of them. More ohms in that leg means a longer turn and a lower note — 135 Hz at one end of the knob, 683 Hz at the other.

Wiring

1. 1 → 38
2. 39 → 5
3. 6 → 32
4. 39 → 7
5. 8 → 42
6. 43 → 35
7. 39 → 11
8. 12 → 33
9. 39 → 13
10. 14 → 46
11. 47 → 36
12. 32 → 24

13. 25 → 36
14. 35 → 26
15. 27 → 33
16. 34 → 2
17. 37 → 2

Open it on the bench: ohmsville.com/bench#a=whoopee-siren

Learn more: Classroom, Oscillators, paragraph 5 — ohmsville.com/classroom#oscillators-5

What you should see

The lamp blinks, and the knob sets how fast — about twice a second at the top of its travel, about once every four at the bottom.

Parts

9 V battery, 330 Ω, 1 kΩ, two 10 kΩ, 100 kΩ, two 100 µF, red LED, Q1, Q2, 100 kΩ pot

How it works

The pot is laid across a fixed 100 kΩ rather than in line with it, and two resistances side by side always come to less than the smaller one. Wind the knob to one end and its near-zero ohms short the 100 kΩ out, so the capacitor refills fast and the lamp blinks fast; wind it to the other and the pair is about 50 kΩ, and each blink takes four times as long. Putting a resistor beside another lowers the total, and here you can watch it happen.

Wiring

1. 1 → 5
2. 6 → 28
3. 29 → 32
4. 1 → 9
5. 10 → 35
6. 1 → 11
7. 12 → 33
8. 1 → 13
9. 14 → 15
10. 16 → 36
11. 15 → 46
12. 47 → 16

13. 32 → 20
14. 21 → 36
15. 35 → 22
16. 23 → 33
17. 34 → 2
18. 37 → 2

Open it on the bench: ohmsville.com/bench#a=heritage-rate-knob

Learn more: Classroom, Series and parallel, paragraph 4 — ohmsville.com/classroom#series-and-parallel-4

What you should see

Nothing happens for about seven seconds. Then the lamp comes on, all at once, and stays on.

Parts

9 V battery, 100 kΩ, 470 µF, 330 Ω, red LED, Q1, Q2

How it works

The 470 µF fills through a 100 kΩ, and that pair has a time constant of about forty-seven seconds, so the voltage on the capacitor crawls. Two transistors nose to tail need about 1.4 V to start, and once they start they need almost nothing to stay on. So nothing happens for six or seven seconds, then the lamp snaps to full brightness and stays there.

Wiring

1. 1 → 15
2. 16 → 46
3. 47 → 2
4. 16 → 33
5. 1 → 32
6. 34 → 36
7. 1 → 5
8. 6 → 28
9. 29 → 35
10. 37 → 2

Open it on the bench: ohmsville.com/bench#a=heritage-slow-fuse

Learn more: Classroom, Capacitors and time, paragraph 2 — ohmsville.com/classroom#capacitors-and-time-2

What you should see

Two 1 µF capacitors nose to tail give the higher note. Slide the switch to jump one of them out and the note drops by about a fifth.

Parts

9 V battery, two 330 Ω, 1 kΩ, 10 kΩ, 0.1 µF, two 1 µF, Q1, Q2, speaker, slide switch

How it works

Two capacitors nose to tail act as one smaller capacitor, the opposite of what resistors do in series: the same charge has to push through both, so each takes half the voltage and the pair behaves like half a microfarad. Half the bucket fills in half the time, so the note is higher. Close the switch across the second capacitor and the first works alone at its full value, so that half of the cycle doubles and the note falls.

Wiring

1. 1 → 5
2. 6 → 32
3. 1 → 7
4. 8 → 42
5. 43 → 35
6. 1 → 13
7. 14 → 33
8. 1 → 9
9. 10 → 36
10. 32 → 46
11. 47 → 48
12. 49 → 36

13. 47 → 40
14. 41 → 36
15. 35 → 26
16. 27 → 33
17. 34 → 2
18. 37 → 2

Open it on the bench: ohmsville.com/bench#a=heritage-two-buckets

Learn more: Classroom, Series and parallel, paragraph 4 — ohmsville.com/classroom#series-and-parallel-4

What you should see

Hold the key and the tone climbs by half. Let go and it drops straight back.

Parts

9 V battery, two 330 Ω, two 10 kΩ, 4.7 kΩ, two 0.1 µF, Q1, Q2, speaker, pushbutton

How it works

Hold the key and the 4.7 kΩ becomes a second road beside the 10 kΩ that feeds one base. Two resistances side by side always total less than either alone, about 3.2 kΩ here, so that half of the cycle refills three times as fast and the pitch climbs by half. Adding a resistor made the resistance smaller, and you can hear it.

Wiring

1. 1 → 5
2. 6 → 32
3. 1 → 7
4. 8 → 42
5. 43 → 35
6. 1 → 11
7. 12 → 33
8. 1 → 13
9. 14 → 36
10. 11 → 38
11. 39 → 46
12. 47 → 12

13. 32 → 24
14. 25 → 36
15. 35 → 26
16. 27 → 33
17. 34 → 2
18. 37 → 2

Open it on the bench: ohmsville.com/bench#a=heritage-parallel-trick

Learn more: Classroom, Series and parallel, paragraph 4 — ohmsville.com/classroom#series-and-parallel-4