Motor direction controller
Description: This circuit can control a small DC motor, like the one in a tape recorder. When both the points A & B are "HIGH" Q1 and Q2 are in saturation. Hence the bases of Q3 to Q6 are grounded. Hence Q3, Q5 are OFF and Q4, Q6 are ON. The voltages at both the motor terminals is the same and hence the motor is OFF. Similarly when both A and B are "LOW" the motor is OFF. When A is HIGH and B is LOW, Q1 saturates, Q2 is OFF. The bases of Q3 and Q4 are grounded and that of Q4 and Q5 are HIGH. Hence Q4 and Q5 conduct making the right terminal of the motor more positive than the left and the motor is ON. When A is LOW and B is HIGH, the left terminal of the motor is more positive than the right and the motor rotates in the reverse direction. I could have used only the SL/SK100s, but the ones I used had a very low hFE ~70 and they would enter the active region for 3V (2.9V was what I got from the computer for a HIGH), so I had to use the BC148s. You can ditch the BC148 if you have a SL/SK100 with a decent value of hFE (like 150). The diodes protect the transistors from surge produced due to the sudden reversal of the motor.
This circuit utilizes a combination of transistors and diodes to control the direction of a small DC motor, commonly found in devices such as tape recorders. The circuit operates based on the logical states of two input points, A and B.
When both A and B are HIGH, transistors Q1 and Q2 enter saturation, grounding the bases of transistors Q3 to Q6. Consequently, Q3 and Q5 are turned OFF, while Q4 and Q6 are ON. This condition results in equal voltage at both terminals of the motor, effectively keeping it in an OFF state. Conversely, when both A and B are LOW, the motor remains OFF as well.
The circuit allows for directional control of the motor. When A is HIGH and B is LOW, Q1 saturates while Q2 remains OFF. In this configuration, the bases of transistors Q3 and Q4 are grounded, while Q4 and Q5 receive HIGH signals. This causes Q4 and Q5 to conduct, making the right terminal of the motor more positive than the left, thus turning the motor ON in one direction.
In the opposite scenario, when A is LOW and B is HIGH, the left terminal of the motor becomes more positive than the right terminal, resulting in the motor rotating in the reverse direction.
The choice of transistors is critical to the circuit's performance. While SL/SK100 transistors could have been used, the selected transistors had a low current gain (hFE) of approximately 70, which necessitated the use of BC148 transistors. If a SL/SK100 with a higher hFE of around 150 is available, the BC148 transistors may be omitted.
Additionally, diodes are incorporated into the design to safeguard the transistors from voltage surges that occur during the rapid reversal of motor direction, ensuring the longevity and reliability of the circuit. This protection is vital in preventing damage to the transistor components from inductive kickback generated by the motor.This circuit can control a small DC motor, like the one in a tape recorder. When both the points A & B are "HIGH" Q1 and Q2 are in saturation. Hence the bases of Q3 to Q6 are grounded. Hence Q3,Q5 are OFF and Q4,Q6 are ON . The voltages at both the motor terminals is the same and hence the motor is OFF. Similarly when both A and B are "LOW" the motor is OFF. When A is HIGH and B is LOW, Q1 saturates ,Q2 is OFF. The bases of Q3 and Q4 are grounded and that of Q4 and Q5 are HIGH. Hence Q4 and Q5 conduct making the right terminal of the motor more positive than the left and the motor is ON. When A is LOW and B is HIGH ,the left terminal of the motor is more positive than the right and the motor rotates in the reverse direction. I could have used only the SL/SK100s ,but the ones I used had a very low hFE ~70 and they would enter the active region for 3V(2.9V was what I got from the computer for a HIGH),so I had to use the BC148s .
You can ditch the BC148 if you have a SL/SK100 with a decent value of hFE ( like 150).The diodes protect the transistors from surge produced due to the sudden reversal of the motor.
This circuit utilizes a combination of transistors and diodes to control the direction of a small DC motor, commonly found in devices such as tape recorders. The circuit operates based on the logical states of two input points, A and B.
When both A and B are HIGH, transistors Q1 and Q2 enter saturation, grounding the bases of transistors Q3 to Q6. Consequently, Q3 and Q5 are turned OFF, while Q4 and Q6 are ON. This condition results in equal voltage at both terminals of the motor, effectively keeping it in an OFF state. Conversely, when both A and B are LOW, the motor remains OFF as well.
The circuit allows for directional control of the motor. When A is HIGH and B is LOW, Q1 saturates while Q2 remains OFF. In this configuration, the bases of transistors Q3 and Q4 are grounded, while Q4 and Q5 receive HIGH signals. This causes Q4 and Q5 to conduct, making the right terminal of the motor more positive than the left, thus turning the motor ON in one direction.
In the opposite scenario, when A is LOW and B is HIGH, the left terminal of the motor becomes more positive than the right terminal, resulting in the motor rotating in the reverse direction.
The choice of transistors is critical to the circuit's performance. While SL/SK100 transistors could have been used, the selected transistors had a low current gain (hFE) of approximately 70, which necessitated the use of BC148 transistors. If a SL/SK100 with a higher hFE of around 150 is available, the BC148 transistors may be omitted.
Additionally, diodes are incorporated into the design to safeguard the transistors from voltage surges that occur during the rapid reversal of motor direction, ensuring the longevity and reliability of the circuit. This protection is vital in preventing damage to the transistor components from inductive kickback generated by the motor.This circuit can control a small DC motor, like the one in a tape recorder. When both the points A & B are "HIGH" Q1 and Q2 are in saturation. Hence the bases of Q3 to Q6 are grounded. Hence Q3,Q5 are OFF and Q4,Q6 are ON . The voltages at both the motor terminals is the same and hence the motor is OFF. Similarly when both A and B are "LOW" the motor is OFF. When A is HIGH and B is LOW, Q1 saturates ,Q2 is OFF. The bases of Q3 and Q4 are grounded and that of Q4 and Q5 are HIGH. Hence Q4 and Q5 conduct making the right terminal of the motor more positive than the left and the motor is ON. When A is LOW and B is HIGH ,the left terminal of the motor is more positive than the right and the motor rotates in the reverse direction. I could have used only the SL/SK100s ,but the ones I used had a very low hFE ~70 and they would enter the active region for 3V(2.9V was what I got from the computer for a HIGH),so I had to use the BC148s .
You can ditch the BC148 if you have a SL/SK100 with a decent value of hFE ( like 150).The diodes protect the transistors from surge produced due to the sudden reversal of the motor.
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