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Yes, you can build a small sun-tracking solar panel with an Arduino. The simplest useful dual-axis design uses four LDRs arranged around a shaded cross, an Arduino Uno or classic Nano, two hobby servos, and a lightweight pan-tilt mount. The Arduino compares the top, bottom, left, and right light levels, then makes small corrections toward the brighter side.
That design is ideal for a supervised tabletop experiment. It is not a guaranteed efficiency upgrade and should not be treated as a roof-ready construction or PV mounting system without engineered structure, weather protection, actuator protection, and a measured energy budget.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchWhat a sun-tracking Arduino panel does
A sun tracker rotates a photovoltaic panel so its surface stays more nearly perpendicular to incoming sunlight. For a small two-axis demonstrator, an Arduino reads four light-dependent resistors (LDRs), compares the light reaching each quadrant, and nudges two servos until the top and bottom readings—and the left and right readings—are nearly equal.
This is a useful low-voltage mechatronics project, but it is not automatically a better solar system. A tracker consumes energy, adds moving parts, and must withstand wind, rain, cable movement, and mechanical loads. A documented Arduino Blog experiment observed about 15% more energy than a fixed panel during a short 2.5-hour comparison, but that was a project-specific result. Time of day, weather, panel orientation, and the tracker’s own power consumption can change the outcome substantially.
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- ATmega328P Microcontroller: Powered by the reliable ATmega328P, running at 16 MHz with 32KB of flash memory, 2KB SRAM, and 1KB EEPROM, offering ample resources for a wide range of basic to advanced electronics projects.
- 14 Digital I/O Pins & 6 Analog Inputs: Features 14 digital I/O pins (6 of which support PWM output) and 6 analog inputs (10-bit resolution), providing flexible options for sensors, motors, and other external components.
- USB Connectivity for Easy Programming: The built-in USB port allows for direct programming and serial communication, enabling a simple connection to your computer for sketch uploading and debugging through the Arduino IDE.
- Compatible with Arduino IDE: Full compatibility with the Arduino IDE ensures easy access to a vast array of libraries, code examples, and community-driven projects, making the Uno a great choice for both beginners and experienced makers.
- Widely Used in Education & Prototyping: The Arduino Uno is a standard in educational environments, widely used for learning and teaching electronics and programming. It's perfect for prototyping, robotics, IoT projects, and more.
Single-axis or dual-axis tracking?
| Design | What moves | Typical beginner hardware | Trade-off |
|---|---|---|---|
| Single axis | One rotation, commonly east to west | Two LDRs or two opposing sensor groups and one actuator | Simpler, lighter, and usually easier to power, but it does not correct both daily and seasonal angle changes |
| Dual axis | Pan and tilt | Four LDRs, two servos, and a pan-tilt mechanism | Demonstrates full directional correction, but has more backlash, wiring, control complexity, and actuator energy use |
The build below is a dual-axis tabletop design. If the panel is too heavy for hobby servos, a single-axis design or a properly sized linear actuator and motor driver is safer than simply installing larger servos and hoping the Arduino can power them.
Parts list for a small prototype
Use a lightweight, low-voltage panel for the first test. Do not begin with a residential PV module or a roof-mounted frame.
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- Arduino Uno R3 or a classic Arduino Nano. The Uno offers six analog inputs and full-size connectors. The classic Nano is breadboard-friendly and has eight analog inputs, but newer Nano models use different processors and voltage levels, so identify the exact board before wiring it.
- Four LDRs. A photoresistor LDR pack is convenient when the four sensors need to be reasonably similar.
- Four fixed resistors. A 10 kΩ resistor assortment is a sensible starting point, not a universal value for every LDR.
- Two 5 V micro servos for a very light panel and mechanism. Confirm the selected servo’s allowable voltage, torque, travel, and current requirements before buying around a listing.
- A two-axis pan-tilt bracket, servo horns, screws, and a rigid base. The bracket must support the panel without allowing the servo shaft to carry excessive bending load.
- A small 5 V solar panel for the educational experiment. The panel’s voltage and current depend on its construction and lighting conditions.
- Breadboard and jumper wires for indoor testing.
- A regulated 5 V servo power supply when the servos are mechanically loaded or more than one servo is being driven.
- A multimeter for checking divider voltages, supply voltage, and panel output.
- Optional: current sensor, limit switches, real-time clock, compass, battery, charge controller, or data logging hardware for a more advanced tracker.
The Uno, Nano, sensors, resistors, servos, bracket, panel, power supply, and multimeter serve different purposes. The controller reads and decides; the LDR network detects direction; the servos provide motion; and the frame transfers that motion to the panel.
How the four-LDR sensor finds the sun
Arrange the LDRs in four quadrants around a small vertical cross or shade:
+-------------------+
| upper-left | upper-right |
| LDR | LDR |
|-------------------+----------------
| lower-left | lower-right |
| LDR | LDR |
+-------------------+The divider must be tall enough to cast a different shadow when the light arrives from one side, but not so tall that the sensor becomes unusably insensitive. Mount the sensor assembly so its centerline is parallel to the panel’s intended normal direction.
Each LDR is one half of a voltage divider. A common arrangement is:
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesregulated 5 V ── LDR ── analog node ── 10 kΩ resistor ── GNDConnect the analog node to an Arduino analog input. With this arrangement, a brighter LDR normally produces a higher ADC reading. If the fixed resistor and LDR are reversed, brighter light produces a lower reading instead; either arrangement works, but all four dividers must be wired consistently and the control logic must be inverted if necessary.
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- Original ATmega328P CH340 chip is used. Improved new version CH340G Replace FT232RL.
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- Works the same as original Nano, runs perfectly on programming software.
- Using Atmel Atmega328P-AU MCU, Support ISP download; Support USB download and Power.
- LAFVIN Nano CH340 controller is a compact board similar to the R3 board, smaller and breadboard-friendly than Diecimila.
The resistor value controls the useful sensitivity range. LDR resistance varies widely between components and lighting conditions, so 10 kΩ is a starting value rather than a specification. Use the Serial Monitor or a multimeter to check that the readings change clearly when a lamp moves from one quadrant to another.
Mechanical design comes before fine-tuning the code
Attach the panel close to the pan axis and keep its center of gravity near the tilt axis. A flexible bracket, loose servo horn, or long cantilever turns a small correction into visible shaking. Keep the panel light for the first version, tighten the fasteners, and make sure the wires cannot wrap around either axis.
Set software limits below the servo’s nominal end stops and install physical hard stops that prevent dangerous travel even if the program fails. The exact safe angle depends on the bracket, servo, panel, and wire routing; the 15° to 165° limits in the example code are only conservative starting values.
Standard hobby servos are commonly specified for an approximately 0° to 180° shaft range, but the usable range is model- and mechanism-dependent. A servo that is commanded against a stop can draw high current, overheat, strip its gears, or reset the Arduino.
Power the servos separately when necessary
Do not use an Arduino I/O pin to power a mechanically loaded servo. The Arduino Servo documentation warns that servos can draw considerable current; a separate supply is generally needed when driving more than one or two servos or when the load is significant.
For the tabletop build, power the Arduino through USB or another appropriate regulated input. Power the servos from a separate regulated supply selected for the servos’ voltage and transient or stall-current demand. Connect the external supply ground to Arduino GND so the servo signal has a common reference.
Arduino GND ───────────── external servo-supply GND
external 5 V ───────────── servo power wires
Arduino D9 ────────────── horizontal servo signal
Arduino D10 ────────────── vertical servo signalA solar panel should not be connected directly to the Arduino or servos simply because its label says 5 V. Check its open-circuit voltage, operating voltage, current, and behavior under load. A real outdoor system may need a battery, regulator, charge controller, fuse, and separate power path for the controller and actuators.
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Arduino wiring plan
| Component | Connection | Important detail |
|---|---|---|
| Upper-left LDR divider | A0 | Use the same divider orientation as the other three sensors |
| Upper-right LDR divider | A1 | Keep the sensor physically in the matching quadrant |
| Lower-right LDR divider | A2 | Do not assume the physical order if the sensor board is rotated |
| Lower-left LDR divider | A3 | Verify with Serial Monitor before moving the servos |
| Horizontal servo signal | D9 | Change the constant in code if another digital pin is more convenient |
| Vertical servo signal | D10 | Connect power and ground to the servo supply, not an I/O pin |
| LDR divider supply | Regulated 5 V and Arduino GND | This plan assumes a classic 5 V Uno or classic Nano |
The reference quadrant design uses A0 through A3 for the four photocells and D9 and D10 for the two servo signals. Those pins are not mandatory; they simply make the wiring easy to follow. On most non-Mega boards, the Servo library also disables analogWrite() PWM functionality on pins 9 and 10. That does not prevent those pins from carrying servo control signals, but it matters if the same sketch expects hardware PWM on them for another device.
Control logic: compare averages, not individual sensors
The controller averages the two sensors in each direction:
top = (upper-left + upper-right) / 2
bottom = (lower-left + lower-right) / 2
left = (upper-left + lower-left) / 2
right = (upper-right + lower-right) / 2It then calculates a vertical and horizontal error. If the right average is brighter than the left average, it makes a small pan correction. If the top average is brighter than the bottom average, it makes a small tilt correction. When the difference is small enough, the servo does nothing.
That no-movement region is the deadband. It prevents the tracker from hunting continuously when sensor noise, servo backlash, or changing shadows make the readings fluctuate around equality. Small steps and a short settling delay are also preferable to commanding a large angle jump.
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Install the standard Servo library through the Arduino IDE if it is not already available. Upload this sketch after checking the servo supply and disconnecting the panel mechanism if you need to verify sensor readings first.
#include <Servo.h>
const byte UL_PIN = A0;
const byte UR_PIN = A1;
const byte LR_PIN = A2;
const byte LL_PIN = A3;
const byte PAN_PIN = 9;
const byte TILT_PIN = 10;
Servo panServo;
Servo tiltServo;
int panAngle = 90;
int tiltAngle = 90;
const int PAN_MIN = 15;
const int PAN_MAX = 165;
const int TILT_MIN = 15;
const int TILT_MAX = 165;
const int PARK_PAN = 90;
const int PARK_TILT = 90;
const int STEP_SIZE = 1;
const int DEAD_BAND = 18;
const int LOW_LIGHT = 60;
const byte SAMPLES = 4;
// Reverse either value if that servo moves away from the brighter quadrant.
const int PAN_SIGN = 1;
const int TILT_SIGN = 1;
// Add small correction values after comparing all four sensors in even light.
const int UL_BIAS = 0;
const int UR_BIAS = 0;
const int LR_BIAS = 0;
const int LL_BIAS = 0;
bool parked = false;
int averagedRead(byte pin) {
long total = 0;
for (byte i = 0; i < SAMPLES; i++) {
total += analogRead(pin);
delayMicroseconds(300);
}
return total / SAMPLES;
}
void writePosition() {
panAngle = constrain(panAngle, PAN_MIN, PAN_MAX);
tiltAngle = constrain(tiltAngle, TILT_MIN, TILT_MAX);
panServo.write(panAngle);
tiltServo.write(tiltAngle);
}
void setup() {
Serial.begin(115200);
panServo.attach(PAN_PIN);
tiltServo.attach(TILT_PIN);
writePosition();
delay(500);
}
void loop() {
int ul = averagedRead(UL_PIN) + UL_BIAS;
int ur = averagedRead(UR_PIN) + UR_BIAS;
int lr = averagedRead(LR_PIN) + LR_BIAS;
int ll = averagedRead(LL_PIN) + LL_BIAS;
int averageLight = (ul + ur + lr + ll) / 4;
if (averageLight < LOW_LIGHT) {
if (!parked) {
panAngle = PARK_PAN;
tiltAngle = PARK_TILT;
writePosition();
parked = true;
}
delay(1000);
return;
}
parked = false;
int top = (ul + ur) / 2;
int bottom = (ll + lr) / 2;
int left = (ul + ll) / 2;
int right = (ur + lr) / 2;
int verticalError = top - bottom;
int horizontalError = right - left;
if (horizontalError > DEAD_BAND) {
panAngle += PAN_SIGN * STEP_SIZE;
} else if (horizontalError < -DEAD_BAND) {
panAngle -= PAN_SIGN * STEP_SIZE;
}
if (verticalError > DEAD_BAND) {
tiltAngle += TILT_SIGN * STEP_SIZE;
} else if (verticalError < -DEAD_BAND) {
tiltAngle -= TILT_SIGN * STEP_SIZE;
}
writePosition();
Serial.print(ul);
Serial.print('t');
Serial.print(ur);
Serial.print('t');
Serial.print(lr);
Serial.print('t');
Serial.print(ll);
Serial.print('t');
Serial.println(averageLight);
delay(150);
}What to change before relying on the sketch
- Reverse direction: Change
PAN_SIGNorTILT_SIGNfrom1to-1if a servo moves away from the brighter quadrant. - Set real limits: Replace the example minimum and maximum angles with limits that cannot bind the actual bracket or twist the wiring.
- Choose a park position: A neutral 90° position is convenient for a bench. An outdoor tracker should use a tested night or wind-stow position.
- Calibrate mismatch: Place the sensor in even diffuse light, compare readings, and use the bias constants to compensate for repeatable differences. Do not use calibration to hide a damaged or badly shaded sensor.
- Tune the deadband: Increase it if the mechanism oscillates; reduce it only if the tracker consistently stops with an obvious misalignment.
- Adjust the low-light threshold: The value of 60 is an ADC-count starting point, not a universal night-sky measurement. It depends on the divider, board, sensor, and environment.
The code averages four samples per sensor, uses a deadband, moves by one-degree commands, limits travel, and parks in low light. A more weather-resistant design should add explicit sensor saturation handling, watchdog recovery, current or overload detection, limit switches, and a state machine for startup, tracking, night parking, and high-wind parking.
Build and test it in stages
- Test the Arduino and sensor dividers alone. Power the board, open the Serial Monitor at 115200 baud, and shine a lamp on each quadrant. The corresponding reading should change. If the values move in the opposite direction from the code’s assumption, invert the readings in software or reverse every divider consistently.
- Test each servo without the panel attached. Confirm that the servo moves to the center position, then verify the intended direction. Keep fingers clear and stop immediately if the servo buzzes continuously or presses against a stop.
- Connect the external servo supply. Tie its ground to Arduino GND. If the Arduino resets when a servo starts, treat that as a power or wiring fault—not as a software problem to ignore.
- Install the sensor shade and bracket. Make sure the four sensors correspond to the physical quadrants used in the code. Secure the sensor assembly so vibration does not change its geometry.
- Use a lamp indoors. Move the lamp to each side and above or below the sensor. The panel should make small corrections toward the brighter side and settle when the quadrant averages become similar. Indoor lamps do not reproduce the sun perfectly, so use this stage to find wiring and direction errors rather than to estimate solar performance.
- Try direct sunlight under supervision. Keep the panel small, use conservative travel limits, and watch for cable snagging, servo heating, unexpected shadows, and movement caused by wind. Do not leave a prototype unattended outdoors.
- Measure energy rather than only voltage. Record panel voltage and current through the same load while the panel is fixed and while it tracks. Calculate power as
P = V × I, then compare energy over a defined interval. Subtract the controller and actuator energy before deciding whether tracking improved net output.
How to make a fair fixed-versus-tracking comparison
A voltage reading by itself does not establish that one arrangement produced more energy. Use the same panel, load, wiring, and measurement method. Record the date, time, location, weather, panel temperature if available, tracking mode, and how much the servos moved.
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The cleanest small experiment alternates between fixed and tracking runs or uses matched panels measured at the same time. A single morning-versus-afternoon comparison can be dominated by changing clouds and temperature. A useful report should state whether the tracker energy was included and should not turn one short observation into a guaranteed percentage.
For more formal PV modeling, relevant inputs include module electrical characteristics, array topology, geographic coordinates, orientation, row spacing, tracking algorithm, and shading. Those variables explain why a result from one panel and location cannot be transferred directly to a roof, farm, or different season.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Outdoor and construction limitations
A tabletop servo tracker is an educational prototype, not a roof-ready mounting system. Outdoor PV structures need a rigid, durable frame designed for wind, rain, hail, corrosion, long-term vibration, and the weight of the panel. Tracking adds bearings, joints, actuators, control electronics, and maintenance points.
For an outdoor low-voltage experiment, plan for:
- a rigid, weather-resistant frame and a base that cannot tip;
- sealed electronics with appropriate cable glands and strain relief;
- mechanical hard stops independent of the Arduino sketch;
- a tested wind-stow position and a strategy for severe weather;
- flexible cable loops that cannot become pinched or wrapped around an axis;
- current sensing, fusing, or overload protection appropriate to the actuator supply;
- a battery or regulated auxiliary supply if the panel cannot reliably power the control system;
- inspection of fasteners, bearings, servo gears, cable jackets, and corrosion;
- a measurement plan that includes controller, sensor, and actuator consumption.
For a roof or permanent installation, structural attachment, electrical protection, grounding, equipment listing, roof penetrations, and local code requirements need a design appropriate to the jurisdiction and the panel system. A small Arduino and hobby-servo assembly should not be substituted for an engineered PV mounting product.
When to use a more advanced tracker
LDR feedback is attractive because it is inexpensive and intuitive, but it can be fooled by cloud edges, reflections, partial shade, and a nearby lamp. It also loses directional information in very low light. A timer- or position-based tracker can calculate expected solar position without chasing a transient bright patch, although it requires accurate time, location, geometry, and position feedback.
Arduino’s published examples show several ways to move beyond the beginner design. A single-axis installation used LDR pairs, linear actuators, an Arduino Nano RP2040 Connect, and Arduino Cloud logging. Linear actuators are not servos: they generally require a suitable motor driver, external power, position or limit feedback, and protection against overload.
A more sophisticated two-axis concentrating-photovoltaic tracker used an Uno, an MPU-9250 compass, a DS3231 real-time clock, a custom light sensor, two motors, current protection, and hardware stops. Those additions address orientation, timing, overload, and travel—not just light imbalance. They are appropriate topics for a second version, not prerequisites for learning the four-LDR method.
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Common problems and fixes
| Symptom | Likely cause | Correction |
|---|---|---|
| One sensor always reads near 0 or 1023 | Incorrect divider wiring, broken LDR, short, or saturated lighting | Measure the analog node, check the fixed resistor, and compare all four dividers under the same light |
| The panel oscillates | No deadband, large steps, sensor noise, or flexible mechanics | Increase the deadband, average more samples, reduce the step size, add settling time, and stiffen the bracket |
| The tracker moves in the wrong direction | Servo orientation does not match the code | Reverse the relevant sign constant or swap the servo’s mechanical orientation; do not swap sensor labels blindly |
| The Arduino resets when a servo moves | Servo current is pulling down the Arduino supply or the ground reference is missing | Use a properly regulated external servo supply, connect grounds together, shorten or improve power wiring, and check for binding |
| Only one axis works | Wrong pin, detached servo, damaged signal wire, or a travel limit reached | Test the servo independently, verify D9/D10 assignments, and inspect the bracket before changing the algorithm |
| It tracks a bright reflection or cloud edge | The LDR sensor sees local brightness rather than the panel’s best solar angle | Improve the cross-divider geometry, shade the sensor from side reflections, increase the deadband, or move to timed/position-based tracking |
| Outdoor movement is weak or erratic | Wind load, insufficient torque, voltage drop, moisture, or backlash | Reduce panel size, strengthen the mechanism, increase supply capacity within the servo specification, weatherproof the electronics, and add hard stops or stronger actuators |
Bottom line
The most approachable sun-tracking solar panel using an Arduino is a small dual-axis demonstrator: four LDR voltage dividers on A0–A3, two hobby servos on D9 and D10, a lightweight pan-tilt mount, a separate servo supply when required, and a control loop with averages, deadband, small steps, low-light parking, and hard travel limits. Build and validate it indoors first, then measure net energy outdoors under controlled conditions. Treat any percentage gain as specific to the test, and redesign the mechanics, power system, protection, and weatherproofing before considering a permanent construction or PV installation.
Reference basis: The design follows the documented Arduino Uno, classic Nano, and Servo-library capabilities; Arduino-published tracker examples; the quadrant-sensor reference build; and U.S. Department of Energy guidance on PV tracking, structural durability, and performance modeling.
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Will an Arduino sun tracker always generate more electricity?
Tracking does not always produce more net energy. The gain depends on location, season, weather, panel orientation, shading, tracking accuracy, and the energy consumed by the controller and actuators. A short documented Arduino project observed a 15% increase, but that is not a universal guarantee.
Should I use an Arduino Uno or Nano?
The classic Uno is convenient for a first build because it has full-size connectors and six analog inputs. The classic Nano is smaller and breadboard-friendly, with eight analog inputs. Newer Nano variants are not automatically interchangeable because their processors and voltage levels can differ.
Can the Arduino power the servos directly?
Use a regulated external supply for the servos when they are loaded, and connect that supply’s ground to Arduino GND. Do not power a mechanically loaded servo from an Arduino I/O pin. Check the servo specifications when sizing the supply.
What should I do if the panel moves away from the light?
Check the sensor quadrant labels, reverse the appropriate pan or tilt sign in the sketch, and verify that all four dividers produce higher readings in brighter light. Also confirm that the servo is not mounted in the opposite orientation from the code’s assumption.
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Why does my solar tracker constantly oscillate?
Increase the deadband, average more readings, use smaller servo steps, add a longer settling delay, and reduce mechanical flex or backlash. A sensor divider that is too sensitive or unevenly calibrated can also cause hunting.
The Bottom Line
A four-LDR, two-servo Arduino tracker is an excellent small-scale experiment, but it is not a guaranteed energy upgrade or a roof-ready PV mount. Use a deadband, current-safe external servo power, mechanical limits, supervised testing, and a fixed-versus-tracking energy comparison that includes the tracker’s own consumption.
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