Tiny BOT is a simple obstacle avoiding robot with two wheels that can be fabricated using a handful of generally available and inexpensive discrete components. The robot can perform avoidance manoeuvres whenever it detects an obstruction in its path. The electronic part is simple and can be built on a small piece of prototyping board. Although not terribly complicated, the mechanics do require a little care all the same. The drawing shown below details the key parts and elements of the system. Tiny BOT can be fuelled by a 6V (1.5x 4) battery pack.
The Electronics inside the obstacle avoiding robot
Tiny BOT uses a front facing Infrared LED (Tx) to scan its path and a Photodiode (Rx) to detect light reverted from the obstacle by reflection. As soos as an obstruction is detected, Tiny BOT goes into reverse direction, and set off the locomotion in another forward direction. The sensor electronics is wired around the small Op-Amp LM358N (IC1), which is an 8-pin chip having two inbuilt Op-Amps. One part of IC1 used here is configured in comparator mode. The sensitivity of the circuit is controlled by the reference voltage at pin 2 of IC1 using a 10K trimpot (P1). P1 will help to reduce unwanted detections caused by external light sources.
Robot Electronics Parts
The Motor Trick
Normally relay RL1 switches the positive and negative supplies to both motors M1 and M2. In case of an obstruction detection, RL1 switches to reverse the polarity of the motor connections. D2 now becomes reverse biased and hence supply to M2 is not available. Now only M1 goes into reverse mode. When RL1 switches back (no obstacle detection) Tiny BOT returns to the initial condition.
Note that this circuit can detect obstacles upto a distance of 5 – 10 cm. The range depends largely on the reflective properties of the obstacle so black objects will only be seen at very short ranges!