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The problem
Every electronics student eventually needs a variable bench supply: wall adapters give one fixed voltage, linear regulators waste power and still fix the voltage, and powering a prototype at the wrong voltage destroys boards. Commercial CC-CV bench supplies are priced beyond a typical student budget, and cheap adapters give no current limiting — one shorted wire means burnt traces. This project builds a digital bench variable DC power supply around an Arduino Nano. A rotary encoder sets the output in 0.1 V steps (design value), a 16×2 LCD shows set and measured voltage, load current and the active mode, and the firmware implements true CC-CV behavior: constant voltage until the load current reaches the programmed limit, then constant current as the voltage sags. Short circuits latch the output off until reset. It is an explainable instrument — the student can describe the buck stage, feedback injection, current sensing and firmware loop in a viva without hand-waving.
Each detent changes the voltage setpoint by 0.1 V; a press switches to the current-limit setpoint.
Follow the working sequence
How it works
- The operator turns the rotary encoder; each detent changes the voltage setpoint by 0.1 V (design value), and a button press switches the encoder to the current-limit setpoint (0–3 A range, design target).
- A firmware control loop running approximately every 10 ms (design target) converts the voltage setpoint into a PWM duty cycle; an RC low-pass filter (1 kΩ, 10 µF — design values) smooths this into a DC control voltage injected into the buck converter's feedback node.
- The output voltage is sampled through a resistor divider scaled for the Nano's 10-bit ADC using its internal 1.1 V reference (datasheet); the loop trims the PWM to hold the measured voltage at the setpoint — this is constant-voltage mode.
- Load current is measured by an ACS712 Hall-effect sensor (±5 A variant, 185 mV/A — datasheet) and scaled to amperes in firmware; output power is computed from V × I.
- When the measured current reaches the set limit, the firmware switches to constant-current mode: it reduces the PWM drive to hold current constant, the LCD mode flag flips from CV to CC, and the output voltage sags as the load demands.
- On a sudden over-current spike — a shorted load — the firmware latches the converter off, raises a fault message on the LCD, and requires a manual reset; the 3 A slow-blow input fuse (design value) provides hardware backup.
- Four EEPROM presets (3.3/5/9/12 V defaults, user-rewritable) are recalled with the encoder button for the voltages students reach for most often.
Tech stack:
- Arduino Nano (ATmega328P)
- Arduino IDE (C++ firmware)
- DC-DC buck converter module (adjustable)
- ACS712 current sensor
- 16×2 LCD (HD44780)
- Rotary encoder
- 24 V SMPS input adapter
- Perfboard wiring
| Parameter | Value |
|---|---|
| Output voltage range | 0–24 V (design target; input must stay ~2 V above output — expected) |
| Current limit range | 0–3 A (design target, bounded by module rating and wiring) |
| Voltage setting step | 0.1 V (design value) |
| Current limit step | 0.1 A (design value) |
| Voltage display resolution | 0.1 V (design value) |
| Current display resolution | Approximately 0.01 A (expected) |
| Control loop period | Approximately 10 ms (design target) |
| ADC | 10-bit, ATmega328P internal 1.1 V reference (datasheet) |
| Current sensor | ACS712 ±5 A variant, 185 mV/A sensitivity (datasheet) |
| Feedback drive | PWM → RC low-pass (1 kΩ, 10 µF — design values) into buck FB node |
| Input supply | 24–30 V DC SMPS brick (design value) |
| Input fuse | 3 A slow-blow (design value) |
| Presets | 4 EEPROM voltage presets, user-rewritable (design value) |
| Enclosure | Ventilated metal prototype box; Approximately 200 × 150 × 80 mm (typical build) |
Project features
- [Digital voltage control] A rotary encoder sets the output in 0.1 V steps (design value) with the value taking effect live; pressing the encoder switches it to adjust the current limit instead.
- [True CC-CV modes] In constant-voltage mode the output holds the set voltage; when the load current reaches the programmed limit the firmware switches to constant-current mode, holding current steady while voltage sags. The LCD flags the active mode.
- [Live voltage and current readout] A 16×2 LCD shows the set voltage, the measured output voltage, the load current and the CV/CC indicator, refreshed approximately 4 times per second (design target).
- [Short-circuit protection] A sudden over-current event latches the converter output off and raises a fault screen until the user resets; a 3 A slow-blow input fuse (design value) backs up the firmware protection.
- [EEPROM voltage presets] Four user-rewritable presets (default 3.3, 5, 9 and 12 V) are stored in the Nano's EEPROM and recalled from the front panel, retained without power.
- [Multimeter calibration procedure] A documented two-point calibration against the buyer's reference multimeter stores calibration constants in EEPROM, so the displayed values match a real instrument.
- [Filtered-PWM feedback drive] The firmware turns one Nano PWM channel into a smooth control voltage through an RC low-pass filter (1 kΩ, 10 µF — design values) injected into the buck module's feedback node.
- [Prototype enclosure] A ventilated metal box with panel-mount binding posts, the LCD window, the encoder knob and handwritten masking-tape labels — a real bench instrument, not a breadboard demo.
What is included
- Working bench variable DC power supply prototype with digital control and CC-CV
- Arduino firmware source code with comments
- Circuit/wiring diagram and front-panel layout drawing
- Component list with values
- Two-point calibration procedure against a reference multimeter
- Project report PDF (design, firmware logic, calibration, results)
- PPT presentation for final review
- Viva Q&A preparation document (buck converters, CC-CV, feedback, ADC, current sensing)
- Demonstration guidance
Limitations & prerequisites
- Output maximum follows the input: 24 V out needs a 26–30 V input brick (expected), because the buck stage cannot boost above its input.
- Displayed voltage and current are only as accurate as the buyer's two-point calibration against their reference multimeter; some temperature drift is expected.
- 0–3 A is a design target bounded by the buck module rating and wiring gauge, not a measured thermal rating; sustained full-load operation needs the documented heatsinking and ventilation.
- The CC loop is a firmware loop (~10 ms, design target), not an analog control loop — it will not catch microsecond-scale transients; the input fuse is the fast protection.
- This is a prototype instrument, not a certified laboratory supply — no calibration certificate and no industrial/medical certification.
- Input ripple and load-transient response are module-dependent (component-dependent).
- High-current operation needs clear ventilation; the enclosure vents must not be blocked.
Frequently Asked Questions
Which controller is used?
An Arduino Nano (ATmega328P). It reads the rotary encoder, drives the buck module through a filtered-PWM control voltage, samples output voltage and current with its 10-bit ADC, runs the CC-CV loop, and updates the 16×2 LCD.
Is the current limiting real CC-CV?
Yes. CV mode holds the set voltage; when the load current reaches the programmed limit, firmware switches to CC mode and holds current constant while the voltage sags. A short circuit latches the output off until reset.
What feeds the supply?
A 24–30 V DC SMPS brick (design value), specified in the component list. The maximum output is about 2 V below the input because it is a buck stage.
Does it need calibration?
Yes — the deliverables include a two-point calibration procedure against a reference multimeter, and the firmware stores the calibration constants in EEPROM.
Can it be customized?
Yes: an OLED display in place of the 16×2 LCD, more presets, serial logging of V/I to a PC, temperature-based fan control, or a higher-current buck module (needs wiring and thermal redesign).
Is this project suitable for a final-year project?
Yes — for Electronics, E&TC, Electrical and Instrumentation programs. It demonstrates power electronics, feedback control, current sensing, embedded C and instrument design, all explainable end to end in a viva.
Components & software requirements
- Arduino Nano (ATmega328P)
- Arduino IDE (C++ firmware)
- DC-DC buck converter module (adjustable)
- ACS712 current sensor
- 16×2 LCD (HD44780)
- Rotary encoder
- 24 V SMPS input adapter
- Perfboard wiring
Delivery information
Built-to-order project. Delivery timeline is shared after order confirmation based on current queue.
Support terms
Complete documentation, setup guide, and viva preparation included. Support for setup and explanation provided.
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