Need help with intermittent circuit failures - JK Flip Flops

Hi,

I designed this simple circuit where it controls a gearhead motor. The
circuit is supposed to stop the motor for 1 sec (when triggered), and then
upon reactivation, the motor is to change its polarity and spin the opposite
direction, and so-forth.

What the circuit should do:
1) Motor spins (let's just say clockwise) until a timer is triggered.
2) Timer cuts off power to motor breifly (enough time for it to stop
spinning) for 1 sec.
3) 1 sec lapses.
4) Relay then changes state, changing motor polarity.
5) At the same time, power is reapplied to the motor (should spin
anti-clockwise this time).
6) Cycle repeated until timer triggered again.

The motor is to stop briefly before the polarity change-over for obvious
reasons (needs time to stop spinning before changing direction!).
The circuit consists of a 555 timer IC connected as a monostable which is
triggered by a reed switch and magnet (when magnet is nearby, the reed
switch closes and therefore activates the timer). The timer gives out a 1
sec 'high' pulse and then changes back to low state until it is triggered
again by the magnet. The timer's output controls transistors that affect
the behaviour of a JK Flip Flop (for direction control of the motor, via a
DPDT relay), and power for on/off of the motor.

Because I need the JK Flip Flop to change the relay polarity *after* the
motor stops for that 1 sec, I had to somehow invert the output from the 555
so the JK would flip-flop at the right time. Instead of using a 4069
inverter IC to do this, I connected up a couple of transistors with pull-up
resistors to achieve this.

The circuit works fine most of the time (like 80%), but it's unreliable, and
I don't know what I can do to make it work properly every time. Most of the
time the relay changes state 1 sec after motor stops (which is correct), but
other times it does other wierd things, like the relay would act as if it's
connected directly to the 555's output pin. Also, llthough very rare, the
JK Flip Flop would even ignore the clock signals it receives and therefore
the relay would do nothing - only the motor would stop for the 1 sec. Very
annoying, being intermittent faults.

I can forward a circuit schematic, but its too hard to draw in html format
(it's a little too complex) to do. I have a proper schematic i could email
though as a jpeg.

Anyone have any ideas? I need this thing to be reliable. I may be doing
something wrong?

Thanks,

Jason.


.

Relevant Pages

  • Re: Tech EM: Gottlieb Spirit of 76 multiple issues
    ... Yes, on SO76, the left and right pops are fired on the same circuit. ... Something happens on the PF to close a switch. ... The relay will cause the score motor to run and by virtue ... The motor runs until the cam at motor 1C drops into it's slot, ...
    (rec.games.pinball)
  • Re: Need help with intermittent circuit failures - JK Flip Flops
    ... I designed this simple circuit where it controls a gearhead motor. ... Motor spins until a timer is triggered. ... Relay then changes state, ...
    (sci.electronics.basics)
  • Re: motor starting and reversing.
    ... A bit more thought and several more bits of paper and I reckon this circuit ... the FWD or REV button and the relevant relay making contact (about ... relay is 75% of its nominal voltage but some will work at a much lower ... the start winding of the motor. ...
    (uk.rec.models.engineering)
  • Re: motor starting and reversing.
    ... the forward relay, once energised, breaks the circuit for the reverse button ... A bit more thought and several more bits of paper and I reckon this circuit ... that applying mains to the motor terminals 1&4 when the circuit, ...
    (uk.rec.models.engineering)
  • Re: Why two fuses for a 5 ton residential AC?
    ... OUTDOOR FAN MOTOR FLA 2.0 ... MAX FUSE OR HACR TYPE CKT BKR SIZE 60/60 AMP ... OUTDOOR CIRCUIT FACTORY CHARGE 118 OZ R22 ... and the 60 AMP SLO-LAG fuses at the shutoff box at the compressor. ...
    (rec.crafts.metalworking)