Posted by Circuits Arena on Wednesday, 25 January 2017
Digital Tachometer using 8051 Microcontroller-Contactless type is the artlcle explaining Digital Tachometer using 8051 Microcontroller A tachometer is basically used to measure angular speed of a motor. It ca...
Digital Tachometer using 8051 Microcontroller
A tachometer is basically used to measure
angular speed of a motor. It can be mechanical device with a warm gear
and spindle arrangement or a electrical device which converts the
angular speed into electrical signal. The electrical tachometer in turn
can be an AC tachometer or a DC tachometer. While a conventional
tachometer is a contact tachometer which can produce erroneous results
due to change in contact parameters, a digital tachometer is preferred
which doesn’t requires any contact with the device whose speed is to be
measured. It basically works on the principle of retro reflective
scanning, wherein a light source device like LED transmits light signal
to the retro reflective target device which reflects the light, which is
in turn received by the light detector.
Circuit Diagram of Non Contact Digital Tachometer:
How to Design Digital Tachometer:
Sensor Circuit Design: The
sensor circuit consists of the white LED, a phototransistor and a
timer. The timer circuit is designed such that the 7555 timer operates
in monostable mode with a timing of at least 11m sec. Given the time
period, T = 1.1 RC and assuming C to be 1uF, we found R to be equal to
10K. Here select a 1uF electrolyte capacitor and a resistor of 100K
ohms.
Keeping in
view the phototransistor load resistor to be less than Vcc/Ic (Ic being
the collector current of 2N5777) and the value of Vcc and Ic being 5V
and 1mA respectively, we select the resistor value to be 2K ohms.
Controller Circuit Design: The
controller circuit consists of the microcontroller and its interfaces.
Here we chose AT89C51 microcontroller. Microcontroller reset circuit
consists of a resistor and a capacitor with values such that the voltage
at the reset pin doesn’t falls below 1.2V and the timing constant is
never less than 100ms.
Here we
select a 10K resistor and 10uF capacitor. Since microcontroller
oscillating frequency here is 12MHz, we select the values of ceramic
capacitors to be 15pF.
The
interfacing is accomplished by connecting the 7555 output pin to port
pin P0.0 and the LCD display to ports P1 and P2 such that the data pins
of the LCD are connected to port P2 and the command pins are connected
to P1.
