Motorized Video Camera Mount

The camera rotator circuit uses a 2716 EPROM to store a table of logic values that control the motor driver (H-bridge) circuit. The EPROM data is shown in the schematic. By using the EPROM, a large number of discrete gates are eliminated. The logic table is designed to allow the motor to turn clockwise until the clockwise limit sensor is activated
Motorized Video Camera Mount - schematic

. The same operation happens with counter clockwise rotation and the counter clockwise limit sensor. Four bits of input come from the limit sensors and the direction control switch, these go to the EPROM address lines. All of the input signals are low-active. Four EPROM outputs go to the four H-bridge transistor gates. The control switch signals are buffered through the 7400 quad NAND gate, this allows for a long control wire. The control wire should be a shielded type such as beldfoil and the shield should be grounded at only one side. The H-bridge array consists of two N-channel MOSFETs and two P-channel MOSFETs. Diagonal pairs of transistors are turned on to move the motor one way or the other. If all of the transistors are off, the motor does not move. Note that the P channel transistors turn on with a 0 logic output level and the N channel transistors turn on with a 1 logic output level. There are several disallowed output states, if the wrong two transistors are turned on, the transistors and voltage regulator would heat up and possibly be destroyed. Don`t do this. If the EPROM is programmed correctly, this should never happen.

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