Design and construction of microprocessor based remote speed measurement, monitoring and control of d. C motor

1.5 METHODOLOGY
To achieve this project, the design is divided into two major parts: the transmitter section and receiver section as illustrated in the block diagram below.

The transmitter section comprises of sensor, Operational amplifier and ASK transmitter and the receiver section comprises of ASK receiver, Processing unit (including monitoring and control) and Display unit. The circuit diagram of the Transmitter section and the Receiver section is shown in Figure 1(a) and 1(b), respectively. The components that will used are infrared (IR) sensor which is a reflective sensor that includes an infrared emitter and PIN photodiode in a surface mount package which blocks visible light and there is complete optical isolation between the emitter and the photodiode. To convert angular velocity into the corresponding frequency a small reflective strip will be placed on the rotating object which can then be detected by the sensor whenever it passes from its front. Whenever the reflective strip passes from the front of the sensor, some part of IR light gets reflected from it which increases the voltage across the Photo-diode. The output produced by the sensor will be fed into non-inverting terminal of the operational amplifier (op-amp) LM 358 IC set to operate as a non-inverting comparator. Input Voltages “V_Q” and reference Voltage “V_P” is compared by the op-amp whose output depends on the difference between the two voltages. Voltage V_P is set at 2 Volts by making use of zener diode voltage regulator (shunt-voltage regulator configuration), which is fed via inverting terminal of the LM358 comparator. For wireless transmission, the comparator’s output, is connected to the ‘DATA’ pin of the ASK transmitter IC “TX-433”, which transmits the signal at 433 MHz. For the reception of the transmitted ASK modulated signal RX-433 RF IC is used. Both TX-433 and RX-433 supports a data rate of up to 10Kbps, which is sufficient for this design. The demodulated output of the RX-433 is then fed to the processing unit, which consists of a microcontroller “8051” manufactured by ATMEL CORPORATION where most of the calculations are done through a well written code.

Figure 1(a): Transmitter Section

Figure 1(b): Receiver Section
A provision for controlling the motor speed using a potentiometer will be also included in the circuit. This includes transistors (H- bridge) used for driving the motor and its base will be connected to pulse width modulation (PWM) pin 9 of the 8051 microcontroller through the current limiting resistor R1. Wiper of the speed control potentiometer (POT) is then connected to analog pin A0 of the 8051.

The input to the microcontroller is basically a train of pulses where each pulse corresponds to one revolution, thus the total number of pulses in one second corresponds to the Revolutions per Second (RPS) of the spinning object.

The inbuilt counter and timer of the 8051 IC are used to calculate number of pulses in 1/4th of a second; such three values are first averaged and then converted into RPM. If the average value is ‘R’ i.e. there are R number of pulses in 1/4^th of a second, then the RPS will be ‘4xR’ and the RPM will be ‘4xRx60’. The results obtained from the Processing unit are then fed to the display unit. The display unit can either LCD, 4 digit seven 7 display or computer for data logging through which result 8051 microcontroller are display.