Week 7 and 8 Progress

This chapter 4 shows the design and development of the project. The design is important to develop the best project. This section includes design of remote control circuit (transmitter and receiver), DC motor drive, forward and reverses motor circuit, photoelectric sensor circuit and design of mechanical structure. This is the main part of this project. 

4 Channel RF Remote Control Transmitter

According to Vasilis (2004), the transmitter is constituted by AT90S2323 microcontroller and TLP434A RF transmitter module at 433MHz. This design of the transmitter is suitable for more battery economy and safe transmition of the data.

1. The battery economy is made by the used of power down mode of Automatic Voltage Regulator (AVR). In this case the AVR goes to sleep with less than 1uA (microampere) current and wait for external interrupt on pin PB1 to awake from sleep mode and continue operating. If the S2 key is pressed, the logic of this pin goes to '0' (0V) and AVR awake from sleep mode (because PB1 is INT0) and will check if the S1 key is pressed. If not, the AVR will assume that the S2 is pressed. If yes, the logic of this pin and PB1 (through 1N4148) goes to '0' (0V). When the INT0 pin (PB1) of AVR goes to 0V, the transmitter TLP434A is working. If pressing of the switch S1 or S2 is stopped, the TLP will stop working.

2. The safe transmitted data based on the transmition of 4 bytes with serial form at 2400 bps (bits per seconds). 1st and 2nd byte are for recognition of valid remote control from receiver (like ID bytes), 3rd byte is command byte. The relays status dependent by the value of this byte. Finally, the 4th byte is the checksum of the earlier 3 bytes. 

4 Channel RF Remote Control Receiver

According to Vasilis (2004), the receiver is constituted by RF receiver module RLP434A at 418MHz. The microcontroller AT90S2313 and the 4 relays can handle any electric (or electronic) device up to 10 Amps (the contacts of relays are 10Amp at 250Volts). The RLP434A is an RF receiver module with receipt frequency at 418MHz with ASK modulation. 

There are 4 outputs from this module, the digital, with levels from 0v to VCC (5 volts) and the analog output. Analog output is not used. The transmitters send 4 bytes with 2400bps 4 times and the receivers RLP-434A collect them and move them to AT90S2313 to RxD pin, PD0. The antenna is used a cable of 30 - 35cm long. The reasons to select AT90S2313 (20pins) instead of AT90S2343 (8pins) is because with AT90S2313 it can drive up to 14 relays with future upgrade of the firmware, one relay to each pin.       

The Power Supply of RF Receiver

According to Vasilis (2004), the power supply of RF receiver has 2 voltage regulators, LM7812 and LM7805. The first (12V) is only to turn on the 2 relays and the 2nd (5V) to turn on the AVR microcontroller and the RF receiver module. The LED is the voltage indicator and the 4 capacitors are to flattening the voltage.

Forward and Reverse Motor Circuit

Figure 4.4 shows the forward and reverse motor circuit using NPN transistor and integrated with relay to control a motor. Actually this circuit is an additional circuit for RF remote control receiver. The circuit can be connected to output microcontroller AT90S2313. 

DC Motor Drive

This simple DC motor drive circuit use almost 741 operational amplifier operating as a voltage follower where its non inverting input is connected to the speed and rotation direction of a potentiometer VR1. When VR1 is at mid position, the op-amp output is near zero and both Q1 and Q2 is OFF. When VR1 is turned towards the positive supply side, the output will go positive voltage and Q1 will supply the current to the motor and Q2 will be OFF. When VR1 is turned to the negative supply side, the op-amp output switches to the negative voltage and Q1 will turn OFF and Q2 ON which reverses the rotation of the motor's direction. As the potentiometer VR1 is moved toward either end, the speed increases in whichever direction it is turned (Rakes, 1997).