10-08-2012, 05:03 PM
PC-BASED DC MOTOR SPEED CONTROLLER
PC-BASED DC MOTOR SPEED CONTROLLER.pdf (Size: 78.33 KB / Downloads: 101)
This circuit allows you to control the
speed of a DC motor (in eight levels)
from your PC’s parallel port.
The PC uses a software program to control
the speed of the motor.
The motor is connected to the PC
through an interface circuit. The interface
circuit consists of 1-of-8 decoder IC
74LS138 (IC1), hex inverter ICs 74LS04
(IC2 and IC3), resistor networks, timer IC
555 (IC4) and motor driver transistor SL100
(T1). The decoder IC accepts binary
weighted inputs A0, A1 and A2 at pins 1,
2 and 3, respectively. With active-low enable
input pins 4 and 5 of the decoder
grounded, it provides eight mutually exclusive
active-low outputs (Q0 through
Q7). These outputs are inverted by hex
inverters IC2 and IC3.
R. KARTHICK The resistor network comprising presets
VR1 through VR8, resistors R1 and
R2 and capacitor C1 are the timing components
of timer IC 555 (IC4), which is
configured in astable mode. The output of
IC4 is a square wave, which is fed to the
base of transistor T1 via current-limiting
resistor R3. Transistor T1 is used to drive
the motor.
The pulse-width modulation (PWM)
method is used for efficient control of the
motor. The output of the PC is decoded to
select a particular preset (VR1 through
VR8). The value of the selected preset,
along with resistors R1 and R2 and capacitor
C1, changes the output pulse width
at pin 3 of IC4. Thus the motor speed can
be increased/decreased by choosing a particular
resistance. For high-power motors,
the transistor can be replaced by an IGBT
or a power MOSFET.
The software (speedM.c) is written in
‘C’ language and compiled using Turbo C
compiler.
Initially, when the motor is ‘off,’ the
program prompts you to press ‘Enter’ key
to start the motor. Once you press the
key, the motor starts running at full speed.
After a few seconds, the program asks you
to press any key from the keyboard to go
to the next screen for controlling the speed
of the motor. This screen has options for
increasing and decreasing the motor speed
and also for exiting from the program. For
increasing the speed enter choice 1 and
press ‘Enter’ key, and for decreasing the
speed enter choice 2 and press ‘Enter’ key.
This action changes the speed by one step
at-a-time and the message “Speed decreased”
or “Speed increased” is displayed
on the screen. To go to the main menu,
again press ‘Enter’ key.