Stepper motor driver

[Mooncat]

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?

 

[MP1]

You should post your schematic and board layout if you have it. If you know the specs on the steppers, please also post that. All of this information is needed to properly answer the question that you are asking.

MP

 

[Mooncat]

Here is the circuit I am using

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.

 

[audioguru2]

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.

 

[Mooncat]

Thank you, I'll add the capacitors, remove the relay, and see how it goes.

 

[Mooncat]

Success!  Circuit working well, even though it's still on my breadboard.  The stepper motor becomes hot, more than 35C, is this normal?  Total circuit current is 225mA at 12.25V.

 

[audioguru2]

Most of the circuit's current is used by the motor so it is dissipating 12.25V x 225mA= nearly 2.7W. Maybe it gets hot because it is not designed to be driven with a voltage as high as 12V.

 

[Mooncat]

Good point, the voltage isn't marked on it, I assumed it was a 12V motor.  I'll try it on 5V and see if it's better