autonomous mobile robot capable of avoiding obstacles circuit


Posted on Feb 6, 2014

The infra-red receiver requires the infra-red light to be modulated at 38 kHz, this is quivalent to a period of 26 µs. The specifications on the receiver suggested using a 50% duty cycle. We found however that this did not work the way we intended. To overcome this we reduced the duty cycle to 5%. The infra-red sources used were 6mm infra-red (88


autonomous mobile robot capable of avoiding obstacles circuit
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0 nm) LEDs. Using a bank of four of these LED`s across the front of the robot gave an even coverage in the sensor ’s field of view. To modulate the light we drove the infra red LEDs using a 555 timer chip. This timer was tuned using a trimpot to give exactly 38 kHz, which is the receiver ’s centre frequency, however the receiver is susceptible to frequencies between 25 khz and 60 kHz. The output pin of this timer chip drove the two infra-red LEDs. An ATMEL 89C2051 micro controller was used to control the operation of the dieBot. The benefit of using a micro controller is that the function of the robot can be reprogrammed. This allows for easy design, redevelopment and dubugging. The two inputs to the micro were the outputs from the left and right infra red sensors. There were four outputs from the micro that were connected the motor driving circuit (L293E). The logic of the controller was simple, if the robot sensed a object on the left it would turn right and visa versa. We found difficulties that the robot was very apprehensive when it approached an obstacle. It was found that the ouput signal from the infra red receivers was a digital signal and flickered greatly before changing state. Some form of filtering had to be performed on the input signal. A crude form of filterering was achieved by waiting for the transmitter to detect high for a period of 0. 1 seconds before actually sensing an object. This method of filtering...




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