DC Motor speed control using microprocessor 8085

Introduction

The DC motor is controlled by the microprocessor (8085). The kit used was dynalog 8085 kit.
The DC motor is very difficult to control unlike the stepper motor, which can be controlled by giving the appropriate CONTROL WORD. By knowing the DC motor theory we know the different methods used to control the motor, the most primitive and the once upon a time the most popularly method was WARD-LEONARD motor speed control, but this had many disadvantage, so the world of Electronics brought in the thyristor control, which were very flexible and can be employed to use AC instead of DC cause they had a inbuilt convertor. The thyristor-based system is good but when used with Microprocessor based speed controller they are really good. We have shown the block diagram, circuit diagram used by us to control a small tape recorder sized motor

SPEED CONTROL:-

. The microprocessor takes a feedback from the 'CONTACTLESS INFRARED LED SPEED MEASUREMENT' designed and developed by us. It is similar to a rotary encoder we used only one wooden rigid disc with a hole (even at center for mounting purpose). Then using a sensor (Infrared) like those readily available in the market (we have shown it in diagram) or a common infra LED pair mounted and aligned properly to sense each other. When the DISC rotate the counter starts counting but it increment only when the LED come in sight of each other which is possible when the hole portion of the disc comes in turn we can find the speed of the rotation by proper calibration .The main task of counting, calibrating, calculating, comparing is incorporated in the software used the 8085 system (EPROM).So by comparing the speed reading with the w anted/predetermined speed we can adjust the threshold controlling the DC motor power supply and hence in turn control the DC motor.

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