Builders guide robot pacman.pdf

Figure 15. MC145027 Decoder Block Diagram4.2.2.1 Error detection and filteringThe encoder chip contains nine bits of information. The first fivebits contain the address of the encoder and the other remainingfour bits contain the data bits. These nine bits of information aresent serially to the RF transmitter module. The RF transmittermodule then sends the serial data asynchronously at 418MHz tothe receiver module. For this project, only three out of the fourdata bits were used. The fourth bit was left opened. The decoderreceives the serial data via the RF receiver module, unscramblesthe data and checks to see if two consecutive addresses arematched to the local address of the decoder. Secondly, it checks tosee if the four data bits match the last valid data received. If bothconditions are met, the data bits are outputted to themicrocontroller.Both encoder and decoder chip contain an internal RC oscillator.Since the RF modules were tested and found to operate best forinput frequencies up to 2kHz, the encoder and decoder clockfrequencies were set to approximately 1.7kHz. This resulted in anoutput frequency of approximately 420Hz to the RF modules. Asseen in the figure below, each data bit generated from the encoder12