How to make an inverting amplifier with a chosen gain

Instructional set for introductory electrical engineering students

PURPOSE

Use this guide to design, build, and verify an inverting operational amplifier (op-amp) circuit that produces a controlled and predictable output voltage (Vₒᵤₜ) based on a chosen gain (Aᵥ).

Before you begin

Use this guide when you need to physically implement and test an inverting amplifier using common lab tools, such as a breadboard and National Instruments myDAQ. It is important to note that breadboards connect components in rows called rails, so all components on the same rail are electrically connected. The circuit uses an LM358 Operational Amplifier Integrated Circuit with two resistors (R₁ and R₂) to control gain through negative feedback.

You will:

Select an appropriate gain
Determine resistor values
Build the circuit using an input voltage of +5 V (Vᵢₙ) and power supplies of +/- 15 V from the myDAQ
Measure and verify the output voltage (Vₒᵤₜ)

Figure 1 shows the circuit diagram for the inverting amplifier you can use as a reference. The gain is:

Aᵥ = −R₂/R₁

Figure 1. Reference the inverting amplifier circuit diagram and use it to identify R₁, R₂, Vᵢₙ, Vₒᵤₜ (in red), and the gain equation Aᵥ = −R₂/R₁ (in blue) before building the circuit.

step-by-step instructions

NOTE: Complete the steps in order. Each step builds on the previous one, and skipping steps can result in incorrect gain or circuit failure.

1. Select gain and calculate resistor values

⚠️ CAUTION: If incorrect resistor values are used, the output will not match the expected gain.

Choose the desired amplification level before building the circuit.

1.1) Select a gain (e.g. Aᵥ = -2 V/V) that is low enough to avoid saturation. Considering the myDAQ input voltage and power supplies, it is necessary to choose a gain within -3 V/V to prevent saturation.
1.2) Choose a standard value for R₁ (e.g. 1 kΩ) so that it is accessible.
1.3) Calculate R₂ using the equation for gain:

R₂ = -Aᵥ ⋅ R₁

1.4) Find the actual resistors and confirm their values using the color code chart, shown in Figure 2, or the myDAQ multimeter in resistance mode, shown in Figure 3.

✔ VERIFY BEFORE CONTINUING:

R₂ is correctly calculated from the chosen gain
Selected resistor values match calculated values
Resistors are measured and confirmed

Figure 2. Use the resistor color code chart to identify and verify the correct resistance values for R₁ and R₂.

Figure 3. Measure resistor values using the myDAQ multimeter set to resistance mode (boxed in red) to confirm correct component selection.

2. Identify the op-amp pins

⚠️ CAUTION: Not knowing the pin configuration may result in longer setup times and more wiring errors.

Correct pin identification ensures proper circuit operation.

2.1) Acquire an LM358 Operational Amplifier Integrated Circuit.
2.2) Locate the notch on the LM358.
2.3) Using the pinout diagram in Figure 4, identify:

Inverting input (IN −)
Non-inverting input (IN +)
Output (OUT)
Positive power pin (VCC, pin 8)
Negative power pin (VEE, pin 4)

2.4) Choose one of the two internal op-amps (pins 1-3 or 5-7) and use the corresponding pins consistently.

✔ VERIFY BEFORE CONTINUING:

Inverting, non-inverting, output, and power pins are correctly identified
Chosen op-amp (pins 1–3 or 5–7) is consistent

Figure 4. Identify the LM358 pinout and locate the inverting input, non-inverting input, output, VCC (pin 8), and VEE (pin 4) before wiring the circuit.

3. Place the op-amp on the breadboard

⚠️ CAUTION: An improperly placed op-amp can make debugging more difficult or even destroy the chip.

Prepare the op-amp for wiring.

3.1) Align the notch so that it is on the top of your reference frame.
3.2) Insert the LM358 across the center gap of the breadboard, like shown in Figure 5.
3.3) Ensure each pin is fully inserted and in a separate row.

✔ VERIFY BEFORE CONTINUING:

IC is fully inserted and flat
Each pin is in a separate row
Chip straddles the center gap

Figure 5. Place the LM358 across the center gap of the breadboard with each pin inserted into a separate row.

4. Connect the power supply

⚠️ CAUTION: Ensure the myDAQ is powered OFF at this moment.

4.1) Connect wires to the +15 V and -15 V terminals on the myDAQ. The location of these terminals is shown in Figure 6.
4.2) Insert the +15 V wire into the breadboard rail containing the VCC pin on the LM358 (pin 8).
4.3) Insert the -15 V wire into the breadboard rail containing the VEE pin on the LM358 (pin 4).
4.4) Do NOT plug the myDAQ in yet.

Figure 7 shows the breadboard layout with the power supplies properly connected to the LM358.

✔ VERIFY BEFORE CONTINUING:

+15 V is connected to pin 8 (VCC)
−15 V is connected to pin 4 (VEE)
Power is still OFF

Figure 6. Connect wires to the +15 V and -15 V terminals (boxed in red) on the myDAQ to prepare the power supply for the op-amp.

Figure 7. Connect +15 V (red wire) to pin 8 (VCC) and -15 V (white wire) to pin 4 (VEE) using the breadboard power rails.

5. Connect the input resistor (R₁)

Create the input path to the amplifier.

5.1) Connect a wire to the +5 V terminal on the myDAQ. The location of this terminal is shown in Figure 8.
5.2) Insert this wire into a free breadboard rail. This rail now has a voltage Vᵢₙ.
5.3) Insert one end of R₁ into that rail.
5.4) Connect the other end to the inverting input pin on the LM358 (pin 2 or 6).

Figure 9 shows both ways to set up this portion of the circuit based on whether the first or second op-amp inside the LM358 was chosen.

✔ VERIFY BEFORE CONTINUING: R₁ connects Vᵢₙ to the inverting input pin.

Figure 8. Connect a wire the +5 V terminal (boxed in red) from the myDAQ to prepare Vᵢₙ.

Figure 9. Connect R₁ (highlighted in yellow) between Vᵢₙ (green wire) and the inverting input (pin 2 or 6) to establish the input path of the amplifier.

6. Connect the feedback resistor (R₂)

⚠️ CAUTION: Missing this connection will cause saturation.

Complete the negative feedback loop. Connect R₂ between:

The inverting input pin chosen in Step 5
The output pin corresponding to that inverting input (pin 1 or 7)

Figure 10 shows both ways to set up this portion of the circuit based on whether the first or second op-amp inside the LM358 was chosen.

✔ VERIFY BEFORE CONTINUING:

R₂ connects output to inverting input
Feedback loop is complete

Figure 10. Connect R₂ (highlighted in yellow) between the output (pin 1 or 7) and the inverting input to complete the negative feedback loop.

7. Ground the non-inverting input

Establish a reference voltage.

7.1) Connect a wire to the DGND (ground) terminal on the myDAQ. The location of this terminal is shown in Figure 11.
7.2) Insert it into the row containing the non-inverting input (pin 3 or 5).

Figure 12 shows both ways to set up this portion of the circuit based on whether the first or second op-amp inside the LM358 was chosen.

✔ VERIFY BEFORE CONTINUING: Non-inverting input is directly connected to ground.

Figure 11. Connect a wire to DGND (boxed in red) from the myDAQ to prepare ground.

Figure 12. Connect the non-inverting input (pin 3 or 5) directly to ground (blue wire) to complete the circuit.

8. Verify wiring before power

⚠️ CAUTION: Do not skip this step.

8.1) Compare your breadboard to:

Circuit diagram in Figure 1
Pinout diagram in Figure 4

8.2) Confirm:

Correct resistor placement
Proper power connections
No loose wires

✔ VERIFY BEFORE CONTINUING:

Circuit matches Figure 1 exactly
Power connections are correct (pins 8 and 4)
Input and feedback resistors are correctly placed
No loose or misplaced wires

9. Activate the circuit

⚠️ CAUTION: If components heat up, turn off power immediately.

Plug the myDAQ in. This will supply the input voltage, ground, and power to the circuit.

✔ CHECK: Circuit powers on normally

10. Measure and verify output

Confirm circuit performance.

10.1) Set the myDAQ multimeter to direct current (DC) voltage mode, as shown in Figure 13.
10.2) Place the positive probe (red) from the myDAQ against the output (pin 1 or 7).
10.3) Place the negative probe (black) from the myDAQ against the corresponding non-inverting input (this is grounded).
10.4) Verify:

Vₒᵤₜ = Aᵥ ⋅ Vᵢₙ

Figure 14 shows both ways to measure the output voltage using the multimeter probes based on whether the first or second op-amp inside the LM358 was chosen.

✔ VERIFY FINAL RESULT:

Output voltage is inverted relative to input
Measured gain matches chosen value (e.g. if the chosen Aᵥ = -2 V/V, then Vₒᵤₜ ≈ -10 V)
Output is not saturated (not stuck at ±15 V)

Figure 13. Set the myDAQ multimeter to DC voltage mode (boxed in red) before measuring the output voltage Vₒᵤₜ.

Figure 14. Measure Vₒᵤₜ by placing the red probe on the output pin (1 or 7) and the black probe on the non-inverting input pin (3 or 5, which is grounded).

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