Hacked Tin Can Robot

This is my very first robot, which I made when I was nine. For my birthday I got a simple walking robot Tin Can Robot, which just moved forward and I wanted to hack it so that it could move both directions, change its speed and avoid obstacles. The hack is based on design ideas of my dad and brother, I just did PCB drawing, assembly, soldering and overall setup. 

Function:

The robot is driven by a single geared DC motor and holds a 12-oz soda can. Due to the egg-shaped wheels, its movement resembles a drunken sailor. Its original one AA battery was replaced by a battery-pack of four AA batteries, partially depleted from other toys, to get 4.5 – 5.5 V input voltage. The battery-pack was inserted inside the cut soda can with a PCB. The PCB (universal, line, e=0.1´´) contains a bidirectional motor driver L293D, three 555 ICs for adjusting the sensors and motor speed control and 74HC74 flip-flop IC for motor direction changes.

Motor speed is controlled by 50k potentiometer (P1) at 555 (IC5) input circuit. IC5 sends PWM signal to a bidirectional motor driver L293D, which changes direction of the motor based on a signal from a flip-flop 74HC74 (IC4). The flip-flop changes its output (10 or 01) when it gets a signal from one of IR sensors TSOP4838 positioned on a front side and a back side of the robot in separate boxes. The sensors are modulated for 38 kHz IR signal, which is emitted by IR LEDs placed next to the sensors. The 38 kHz IR signal is generated by another 555 (IC2) using a 10k potentiometer (P2) for precise frequency adjustment. A current in each LED can be set by 10k potentiometers (P3, P4), what defines the range for the obstacle detection (2 - 20 cm). Because TSOP4838 IR sensors can be overloaded by a long 38 kHz signal, the signal generator (IC2) must be interrupted by another 555 (IC3).

The robot walks forward until it approaches the nearest object, the front IR sensor gets a reflection of the IR LED beam, the flip-flop IC changes the direction of the motor driver and the robot walks back until back sensor gets the reflection and then the cycle repeats.

Table of components: 

Functional scheme:

Soldering scheme (universal line PCB; e=0.1´´):

PCB photos:

Back sensor photo:

Overall views:

From today’s perspective, when I already know how to program MCUs, the electronics of this robot seems to be quite complicated compared to what it actually does but it was fun and I liked to solder large PCBs J.