Circuit Lake

Electronic Project and Circuit Collection

RS485 Voting Pad System

12/10/2010 Category: AVR, Digital, Interfacing, Microcontroller, Miscellaneous, Project

This integrated voting system similar to audience poll system on TV game shows, Who Wants to Be a Millionaire. The keypads consist of an ATmega88 microcontroller and a MAX485/DS75176 RS-485 Transceiver. They are connected to a single RS-485 bus using daisy chain topology with CAT5 cables as connector. Keypad nodes are interfaced to the RS-485 bus using a RS-485 to TTL converter. Four push buttons are used to get the input from the audience members. To display the selected option, the keypads is equipped with LEDs.

AVR voting polling system

The RS-485 network is connected to a host PC using a RS-232 to RS-485 bridge which consists of a MAX232 connected to a MAX 485/DS75176. An ATmega88 acts as the sniffer and is responsible for controlling the RX/TX enable of the RS-485 Transceiver. The RTS signal of the PC Serial port was too slow to enable or disable the TX or RX of the transceiver. For redundancy two RS-232 to RS-485 bridges can be connected to two serial ports of the PC with one operational at a time.

The front-end of the system uses of a Java application running on a PC which generates a bar graph to display voting data from audience. The microcontroller firmware is written in Embedded C language and is compiled using WinAVR. This AVR Voting Pad System is designed by Dhananjay Gadre, Sneha Lele, Anurag Chugh, And Parag Shah.