DC circuit analysis

Use the same named connections on your breadboard. Verify which holes share a strip and any power-rail breaks. The transistor drawing labels electrical functions, not left-to-right lead order; the actual manufacturer's package diagram controls placement. Crossing wires without a dot are not connections.

1. Disconnect both pack leads. Measure the isolated LDR in bright light and under an opaque cover. Identify the 10 kΩ and 220 Ω resistors, LED polarity and the actual transistor's B/C/E pins. Never infer pin order from a flat face or a similar part number.
2. Positive → 10 kΩ → base node B. LDR from B → negative. The 10 kΩ must remain in the positive base-feed path.
3. Make the separate LED path: positive → 220 Ω → LED anode A; LED cathode K → collector C. Emitter E → negative. Keep the 220 Ω in series with the LED at all times.
4. Have the instructor check it before power. With the approved nominal 3 V pack, compare a flashlight on the LDR with shading only the LDR. Do not move wiring while powered.
5. Actual sensitivity depends on the LDR, transistor and room light. Both states may still glow; measure the change rather than promising a crisp switch. If there is no clear response, disconnect and check pins, polarity, strips and the isolated LDR readings with the instructor. Do not raise the supply voltage.

1. Use DC volts with leads in V/Ω and COM. Record the loaded source voltage, B-to-E voltage and the 220 Ω resistor drop in light and shade.
2. Use the same lamp distance and opaque cover for repeatable tests. Record actual signs/polarity in your notebook; use the resistor-drop magnitude for current.
3. Keep the LED from illuminating its own LDR, which can change the response. Disconnect both pack leads before any Ω test or wiring correction.

1. LED current in mA = measured voltage across its 220 Ω resistor ÷ that resistor's measured isolated Ω × 1000. Do not use the whole battery voltage: the LED and other devices also have voltage drops.
2. Compare the calculated LED current in light and shade. Explain the separate sensor/base and collector/LED current paths.
3. The transistor loads the sensor circuit. Do not use an unloaded-divider formula as an exact base-voltage prediction, or assume a fixed 0.7 V turn-on voltage, fixed gain or exact LED drop.

Sample numbers only: Illustration only: 0.22 V across a measured 220 Ω resistor gives 1.00 mA; 0.88 V gives 4.00 mA. These are not required sensor readings or guaranteed switching points.

Use the same named connections on your breadboard. Verify which holes share a strip and any power-rail breaks. The transistor drawing labels electrical functions, not left-to-right lead order; the actual manufacturer's package diagram controls placement. Crossing wires without a dot are not connections.

1. Disconnect and take apart the night-light control branch. Keep its LED/220 Ω/collector branch only if it has been checked. Verify the actual B/C/E pins again when repositioning the transistor.
2. Positive → LDR → sensor junction T. Connect one 10 kΩ resistor from T → negative.
3. Connect the SECOND 10 kΩ resistor from T → base B. Do not connect the LDR directly to B: the extra resistor limits the base feed even when the LDR becomes very low resistance.
4. Make the separate LED path: positive → 220 Ω → LED anode A; LED cathode K → collector C. Emitter E → negative. Keep the 220 Ω in series with the LED at all times.
5. Obtain an instructor check, then compare bright light and shade at nominal 3 V. Use only the flashlight/cover while powered. The actual response can be gradual; disconnect for every wiring change.

1. With power disconnected, record isolated LDR resistance in bright light and shade.
2. With the checked build powered, measure T-to-negative, B-to-E and the 220 Ω drop for both light conditions. T and B are different nodes separated by the base-series resistor.
3. Disconnect before correcting anything. If the indicator stays on or off, check the light range, both 10 kΩ placements, transistor pins and LED polarity rather than increasing voltage.

1. LED current in mA = measured voltage across its 220 Ω resistor ÷ that resistor's measured isolated Ω × 1000. Do not use the whole battery voltage: the LED and other devices also have voltage drops.
2. Calculate the base-series current from its own measured 10 kΩ drop divided by its measured resistance. It is not the whole LDR/divider current.
3. The transistor loads the sensor circuit. Do not use an unloaded-divider formula as an exact base-voltage prediction, or assume a fixed 0.7 V turn-on voltage, fixed gain or exact LED drop.

Sample numbers only: Sample only: a 0.80 V drop across a measured 10,000 Ω base-series resistor gives 0.080 mA. A separate 0.66 V across 220 Ω gives 3.00 mA in the LED path; these are different branch currents.

Use the same named connections on your breadboard. Verify which holes share a strip and any power-rail breaks. The transistor drawing labels electrical functions, not left-to-right lead order; the actual manufacturer's package diagram controls placement. Crossing wires without a dot are not connections.

1. Disconnect both pack leads. Identify the pot ends A/B and wiper X with an isolated Ω test. Check the actual pot's track, wiper-current and power ratings with the instructor; skip this build if suitability is unknown.
2. Tie wiper X to the unused end B. Use A and the joined X/B node as the two rheostat terminals. Start at the maximum measured resistance between those terminals.
3. Wire positive → 220 Ω → LED anode A; LED cathode K → pot end A; joined pot X/B → negative. LED A and pot A are terminal names on different parts, not a shared connection.
4. Have the instructor check the circuit. Power from the approved nominal 3 V pack and turn only the insulated knob slowly. The fixed 220 Ω stays in series even at the pot's minimum-resistance setting.

1. At three knob positions, record LED brightness and the DC-voltage drop across the fixed 220 Ω resistor.
2. Disconnect both pack leads before measuring the rheostat resistance; isolate it from the rest of the circuit for the Ω reading, then recheck wiring before repowering.
3. A large 5 kΩ range may leave much of the travel dim. That is useful evidence, not permission to remove the fixed resistor.

1. LED current in mA = measured voltage across its 220 Ω resistor ÷ that resistor's measured isolated Ω × 1000. Do not use the whole battery voltage: the LED and other devices also have voltage drops.
2. Use the measured pot voltage drop × the calculated series current in amperes to estimate power in the active pot segment. This alone does not verify its wiper/track rating.
3. Do not apply source V ÷ (220 + pot Ω) as an exact LED-current result: the LED has a nonlinear voltage drop.

Sample numbers only: Sample: 0.44 V across a measured 220 Ω fixed resistor gives 2.00 mA. Increasing the rheostat resistance should reduce that current in this circuit.

Use the same named connections on your breadboard. Verify which holes share a strip and any power-rail breaks. The transistor drawing labels electrical functions, not left-to-right lead order; the actual manufacturer's package diagram controls placement. Crossing wires without a dot are not connections.

1. Disconnect the pack. Use continuity to identify each switch's two electrical terminals. A four-leg tactile switch often has permanently paired legs: do not assume all four are separate contacts. Skip this build if no suitable switches are available.
2. Wire positive → 220 Ω → LED anode A. Connect LED cathode K to a new node S.
3. Wire switch 1 between S and negative, and switch 2 between the SAME S and negative. The two switches are parallel with each other, not across the pack.
4. Get the instructor's check. Power at nominal 3 V and operate only the buttons. Trace the protected path through the resistor and LED for every closed-button combination.

1. Record the LED state and voltage across the 220 Ω resistor in all four button combinations.
2. Compare one-button and both-button resistor drops under similar battery conditions. Only measure in DC volts while powered; disconnect for continuity or wiring changes.

1. LED current in mA = measured voltage across its 220 Ω resistor ÷ that resistor's measured isolated Ω × 1000. Do not use the whole battery voltage: the LED and other devices also have voltage drops.
2. Calculate LED current for each state. The two buttons provide alternate returns for one LED path, so two pressed buttons do not create two separate LED loads.

Sample numbers only: Expected logic: 00 = off, 10 = on, 01 = on, 11 = on. Sample resistor drop 0.88 V gives 4.00 mA whether one or both return paths are closed, if the other operating conditions stay the same.

Use the same named connections on your breadboard. Verify which holes share a strip and any power-rail breaks. The transistor drawing labels electrical functions, not left-to-right lead order; the actual manufacturer's package diagram controls placement. Crossing wires without a dot are not connections.

1. Disconnect both pack leads. Verify LED polarity, resistor values and the actual switch contacts. Skip this build if suitable switches or the second LED/resistor are unavailable.
2. Branch 1: positive → its own 220 Ω resistor → LED 1 anode; LED 1 cathode → switch 1 → negative.
3. Branch 2: positive → a SECOND 220 Ω resistor → LED 2 anode; LED 2 cathode → switch 2 → negative. Each LED needs its own series resistor: do not share one resistor ahead of both LEDs.
4. Have the instructor check the two source nodes and protected branches. Power at nominal 3 V and test all four switch combinations. Do not add or parallel another battery pack.

1. For each switch combination, record the loaded pack voltage, both resistor drops and which LEDs are lit.
2. One open branch should leave the other branch operating. Small brightness changes can reflect source sag or contacts; record them rather than claiming an ideal battery.
3. Disconnect before moving parts or using Ω mode. Keep this as a small LED build, not a model for connecting building wiring.

1. Calculate I1 = measured drop across resistor 1 ÷ its isolated Ω × 1000, and likewise I2. Then calculate the predicted source total I1 + I2 in mA.
2. Use the drop across each LED's own resistor, not the total source voltage. LEDs are nonlinear loads, so these are not two plain 220 Ω branches.

Sample numbers only: Illustration: 0.88 V / 220 Ω = 4.00 mA in branch 1; 0.66 V / 220 Ω = 3.00 mA in branch 2. Both on: predicted total 7.00 mA. Opening branch 1 leaves branch 2 near its own operating current, subject to source changes.