The Challenge — Autonomous Hazard Response
The goal was to build a physical, autonomous mini-vehicle capable of navigating a simulated maze, detecting a localized flame source, steering towards it, and activating an onboard water pump to extinguish it. The twist? No microcontrollers or code were allowed. The entire control loop had to be hard-wired using analog infrared flame sensors, combinational logic gates, and a motor driver.
The Control Loop — Hard-wired Steering Logic
We positioned three infrared flame sensors at the front of the vehicle: Left, Center, and Right. These sensors evaluate light wavelengths and output a simple logical HIGH or LOW based on the presence of fire. To steer, the outputs of the sensors had to map directly onto the L293D motor driver inputs that control the dual DC motors.
"Without an Arduino to write conditional 'if' statements, the steering logic had to be baked into logic chips. If the left sensor detected a flame, we routed the signal through logic gates to spin the right wheel forward while keeping the left wheel idle, pivoting the chassis toward the heat source."
A center detection triggers both motors forward to charge directly toward the fire, while a proximity threshold triggers a relay to activate the water pump.
The Assembly — Motor Drivers & Pumps
The physical chassis is a 3-wheeled robot base featuring two gear motors and a front caster wheel. The control circuitry is wired on a breadboard mounted to the chassis, housing the logic gates, L293D H-bridge IC, a 5V mini-submersible pump, a small water tank, and a 1-channel relay module.
Physical Engineering — Back-EMF Noise & Voltage Dips
Building robotics on paper is easy; building them in the physical world is messy. During initial testing, the car tracked the flame perfectly. However, the moment the water pump relay clicked on to extinguish the fire, the car spun out of control, resetting its logic states in an endless loop.
"Inductive loads like DC motors and water pumps create massive voltage spikes and electrical noise when switched. This 'back-EMF' was traveling back through our single power rail, dipping the logic gate voltage enough to reboot the chips."
To resolve this, we split the power distribution into two isolated circuits: a 5V power source for the logic gates and H-bridge logic inputs, and a separate 9V battery rail for the DC motors and water pump. Decoupling capacitors (100uF and 0.1uF) were placed directly across the IC power pins to absorb residual electrical noise.
Retrospective — Optocouplers & Weight Distribution
Splitting the battery rails solved the noise issue, but a better approach would have been using optocouplers (like the PC817) to electrically isolate the logic signals from the relay circuits. Furthermore, carrying a heavy liquid payload caused rear-wheel slippage. In a future iteration, I would design a custom 3D-printed chassis with the water tank mounted directly over the driving axles for better traction.