L.I.O.S. is a low-cost, cardboard robot that steers toward a light source by comparing two light-dependent resistor (LDR) readings. Its creator, Oscar Rodriguez Parra, documented a component cost of $10.73; the design pairs a PIC12F683 microcontroller with two modified servos and a small 3.7 V LiPo battery. It is a useful classroom-scale introduction to robotics, but its old parts list and build documentation are not evidence that the same robot can be assembled today for the same price.
What L.I.O.S. is and how it follows light
L.I.O.S. stands for Light Input Output System. Oscar Rodriguez Parra created it as an affordable educational robot for the AFRON design challenge. Its behavior is deliberately simple: two LDRs at the front act as eyes, and the PIC12F683 repeatedly reads their light levels to decide which servo to run.
When the right sensor detects strong light, the robot activates the left servo to turn toward it; the mirrored response applies when light is stronger on the left. When both sensors detect light, both servos run to drive forward. If neither sensor detects light, the robot stops and its LEDs turn off. The paired sensor readings therefore provide basic directional steering rather than image recognition or sophisticated navigation.
Parts and documented cost
Parra’s project documentation reports a total component cost of $10.73. This is the author’s documented parts-cost figure, not a current retail quote; the documentation does not establish that the same total is available from present-day sellers.
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| Part | Role in the build |
|---|---|
| PIC12F683 microcontroller and DIP socket | Reads the sensors and controls the servos and LEDs. |
| Two LDRs and two 10-kilohm resistors | Provide the light-sensing inputs. |
| Two servos | Drive and steer the robot after modification for continuous rotation. |
| Two LEDs and 180-ohm resistors | Indicate sensor-response states. |
| 3.7 V, 130 mAh single-cell LiPo, connector and wire | Supply portable power and connect the circuit. |
| Cardboard, solder, glue and heat-shrink | Form the chassis and support assembly and wiring. |
The chassis and wheels are cut from recycled box cardboard. The original design documentation includes a 1:1 template and a schematic for placing and wiring the servos, sensors, LEDs, resistors, PIC socket and battery connector.
How the build works
Modify the servos
The project uses servos converted from limited 180-degree movement to continuous rotation. The documented conversion removes a gear stop and reworks the potentiometer using a 10-kilohm resistor divider. This is a key mechanical and electrical step: the robot relies on continuous wheel rotation rather than using stock positional servos as-is.
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Assemble the cardboard chassis and circuit
Cut the chassis from the template, then glue the servos and front-facing LDRs in place. Wire the LEDs, resistors, PIC socket, battery connector and servo leads according to the project schematic. Because the design depends on the sensor positions and wheel alignment, follow the template and schematic rather than treating the robot as a generic two-motor chassis.
Compile and program the PIC
Parra supplied C source and HEX firmware for the PIC12F683 and compiled it with SDCC. Programming the chip requires a PIC programmer; the author used a Microchip PICkit3 and notes that lower-cost alternatives exist, without specifying particular alternatives in the documentation. The firmware uses timer timing for servo pulses and ADC conversions to read alternating LDR channels and update the robot’s state. Since the servos face opposite directions, their pulse timing differs.
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What students can learn
The educational value is broader than the robot’s limited behavior. A small build can connect a complete physical system—sensors, controller, drive, power and code—rather than teaching those pieces in isolation. Parra lists learning outcomes across electronics, mechanics, C programming, differential wheeled motion, soldering, CAD, schematic reading, LDR behavior, resistor color codes, voltage and current measurement, component recycling and modification.
- Electronics: interpret a schematic, connect light sensors and resistors, and observe how sensor readings become controller inputs.
- Programming: relate ADC readings and conditional logic to physical movement, and see how timing generates servo pulses.
- Mechanics: understand how two driven wheels produce forward motion and turning, and why servos need modification for this use.
- Practical making: cut and assemble a recycled-cardboard chassis, solder connections and measure voltage or current.
That combination makes L.I.O.S. a short-project teaching example, not a plug-and-play classroom kit: learners must assemble the hardware, modify the servos and program the PIC.
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Performance and practical limits
Parra reports 23 mA while stopped, up to 300 mA while following light, and a speed of 8.7 cm/s at 3.7 V. These are project-author measurements, not independent laboratory benchmarks; the documentation does not establish broader test conditions or results across different surfaces and builds.
The simple drive and cardboard turning flap are intended mainly for smooth flooring, not rough terrain. The original project page also says the robot is not suitable for mass manufacture. Although its design was created for an educational challenge, the available documentation does not establish current retail availability, independent performance testing, classroom adoption numbers or a later maintained version.
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- ✔【School Science Project】: Smart DIY robot car is the most widely used in school for helping students to learn about the soldering project knowledge of mechanical structure, electronic basis skills, the principle of sensor, automatic control, soldering skill and so on.
- ✔【Its Principle】: As the light reflectivity is difererent when the light is emitting on the white and black items. It uses the photoresistance resistance to tell the smart car is on the right way or not. Smart tracking car can discriminate the direction automatically that it can run freely along the black tracking line.
- ✔【Design Your Runway】: You can also use the 1.5~2.0 cm black electrical tape directly on the ground to design the complex runway. It would be even more fun! This educational kit is perfect for holiday gifting and promotes valuable STEM skills!
- ✔【Easy Soldering】: This smart car solder practice kit is easy to build and the principle is simple. The connection that was clearly mapped and labeled on the PCB board. It's much easier to assemble which is great for students, teenagers, beginners and DIY hobbyists.
- ✔【English Manual】: We provide paper English instruction come with the product. You can scan the QR code in the last picture to get PDF manual. You can also download the Installation Manual on the Product Page Named "Technical Specification" Section (Due To Character Limit).
Safety before building
The project uses tools and a LiPo battery that call for care. Parra specifically warns against short-circuiting the battery, charging it above 4.2 V or discharging it below 3 V. The documented construction also involves a trimming knife, needle, hot glue and soldering equipment; the heat-shrink process described uses an open flame. Supervise tool and heat use appropriately, and follow safe LiPo handling and charging practices.
Possible sensor modifications
The documentation describes two ways to change what L.I.O.S. responds to. Replacing the LDRs with CNY70 reflective sensors can adapt it for line following; the code comparison changes from a greater-than threshold to a less-than threshold, and the threshold may need adjustment. Replacing the sensors with snap-action switches makes a collision-detection robot, which the author says requires no source-code change.
Quick Recap
Sources
- Hackaday coverage of L.I.O.S. by Jesse Congdon, October 1, 2012, describes it as an introduction to robotics for classrooms.
- Oscar Rodriguez Parra’s L.I.O.S. project documentation provides the parts list, build instructions, firmware details, measurements and safety notes.
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