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Stepper motor driver


Mooncat

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I am trying to build  a simple circuit to operate a stepper motor at 48 steps per minute.  I am using a 555 to generate clock pulses at 1.25Hz followed by a 4070 and a 4027 to sequence the motor via 4 BFY51s.  But, the clock pulses are too low a level, so I have inserted a sub-min relay to supply a 12volt pulse to step the 4027.  But it doesn't, should it?

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Here is the circuit I am using
steppercircuit.jpg

The relay is so as to produce a full 12volt pulse, not available from a 555 directly, though contact bounce could be possible.  The published circuit uses TIP31's or even 2N3055's but the BFY51 should be suitable for the motor.  The project is to operate a camera shutter, with a cam and follower, for time-lapse photography.

I also built a circuit using a LM324 and a SAA1027, but it is erratic, going into reverse at times.

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I don't see any supply bypass capacitors in your circuit. An ordinary 555 draws a current spike of 400mA when its output switches and the motors also draw a high current so maybe the supply voltage is collapsing for a moment. Then the CD4027 wouldn't work properly. Make sure the supply and ground wiring for the 555 and for the motors can handle the high currents without much voltage drop.
Add a 0.1uF ceramic disc and a 10uF electrolytic at the 555's supply pins, at the CD4027 supply pins and at the motors.

The output high voltage of a 555 is 10.8V with a 12V supply. The minimum input high voltage of a CD4027 is 8.4V with a 12V supply and should be fine without the relay with the bouncing contact. The relay conact didn't provide a logic low anyway.

The circuit might work better with a Cmos 555.

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  • 4 weeks later...

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