1" X 1" 4-bit Digital to Analog Audio Converter

A Digital Analog Converter is a widely used, highly valuable piece of technology. The DAC can be modified to properly fit the requirements of your circuit. They are highly used in the audio and video industry, as they effectively convert signals into visible or audible frequencies. In this project, you will use a DAC to convert a digital input from a computer or phone and convert it into an analog audio using the DACs.

Core Electronic Components

1. LM358 Operational Amplifier (surface-mount)

2. 2.5 kΩ resistor (1206 SMD) – feedback resistor

3. 2x 2.5 kΩ resistor (1206 SMD) – input resistor (R)

4. 5 kΩ resistor (1206 SMD) – input resistor (2R)

5. 10 kΩ resistor (1206 SMD) – input resistor (5R)

6. 20 kΩ resistor (1206 SMD) – input resistor (10R)

PCB & Connectors

7. Custom-designed 1.00" × 0.99" 2-layer PCB (OSH Park fabrication)

8. 3-pin header (for ±12 V power and ground)

9. 4-pin header (DAC inputs)

10. 5-pin header (bit inputs)

11. Audio jack

Tools & Assembly Supplies

12. Wire cutters, strippers, and tweezers

13. Solder paste (for reflow oven)

14. Leaded solder with 6% flux core (for hand soldering)

15. Soldering iron

16. Reflow oven

Testing Equipment

17. Oscilloscope

18. Function generator / waveform generator

19. Arduino (for generating 4-bit digital signals)

20. Binary counter (optional for testing)

21. Logic analyzer

22. ±12 V power supply

23. Speaker (for audio output test)

This DAC is built around an inverting summing amplifier using an op-amp and four binary-weighted resistors. Each input bit passes through a resistor (2.5 kΩ, 5 kΩ, 10 kΩ, 20 kΩ) into the inverting input of the op-amp, with a 2.5 kΩ feedback resistor setting the overall scale. When a bit is high, it contributes current to the inverting node, creating a negative staircase output proportional to the binary value of the inputs.

Collect all necessary parts before starting. You will need an LM358 (or compatible dual op-amp), 1206 package resistors in the specified values, headers for the input, power, and output connections, and an audio jack if you want to test playback. For assembly, prepare solder paste, tweezers, a reflow oven or hot plate for SMD parts, and a fine-tip soldering iron for headers. A bench supply, oscilloscope, and multimeter will also be essential for testing.

Open both the schematic and PCB layout in EAGLE or Fusion 360 and carefully trace the connections. Confirm that the MSB is wired to the smallest resistor (2.5 kΩ) and the LSB to the largest (20 kΩ). Double-check the op-amp orientation and pin assignments, since earlier builds failed when the inverting and non-inverting pins were swapped. Running electrical and design rule checks helps catch common mistakes.

If you don’t already have the PCB made, export Gerber files and send them to a board house like OSH Park. This design was created with their manufacturing rules in mind, so it should pass DRC without issues. Order enough boards to allow for mistakes during soldering, and keep in mind that turnaround time may be a week or more unless you pay for expedited service.

Begin assembly by applying solder paste and placing all the SMD components, including the resistors and op-amp. Reflow these parts in an oven or on a hot plate to secure them properly. Afterward, use a soldering iron to attach through-hole parts like the power header, input header, and audio jack. Clean the board to remove flux residue, and visually inspect each joint to ensure good connections.

Before applying power, perform a continuity check with a multimeter to make sure there are no shorts between the power rails and ground. Once that looks good, connect the board to a ±12 V bench supply with a low current limit (around 50–100 mA) to protect against mistakes. Verify that the correct voltages are present at the op-amp’s power pins and that the output node is stable near zero when no inputs are active.

With the board powered, test the DAC by driving the four input pins with simple binary patterns. You can toggle them manually using jumpers or use a microcontroller like an Arduino to count from 0 to 15 repeatedly. On an oscilloscope, the output should show a staircase waveform with 16 steps. Because this is an inverting design, the staircase will move downward (negative) as higher binary values are applied.

For a full demo, feed 4-bit digital audio into the DAC. A common approach is to have an Arduino sample an audio signal with its ADC, then output the four parallel bits to the DAC inputs. When you view the result on a scope, you should see a stepped approximation of the original waveform. Connect the DAC output to an audio amplifier or powered speaker, and you will be able to hear the audio played back, though at reduced fidelity due to the low resolution.

If the DAC doesn’t behave as expected, start by verifying that each input pin correctly drives its resistor into the op-amp. Make sure the op-amp is oriented correctly and powered with the right rails. If the staircase shape looks distorted or reversed, check that the feedback resistor is the correct value and connected properly. Small issues like cold solder joints, mis-placed resistors, or incorrect bit wiring are the most common causes of errors.