On Tue, 06 Jun 2006 22:54:56 +1000, Jason S wrote:
> 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?
Well, in addition to the bypassing and catch diodes that w2aew mentioned,
I'd say, go ahead and post the schematic on
news:alt.binaries.schematics.electronic ; I notice you're not posting from
google, so I'm assuming you have a real newsserver and a real newsreader.
Put something recognizable in the subject line, and call attention to it
here, or even copy/paste the message ID.
There are also free places where you can post an image, but you'd have to
look them up.
I'd really like to see this circuit, because it sounds like it could be
simplified. One question: does this magnet go past some switch, which
starts the "turn around" process, the motor coasts to a stop, the motor
goes the other way, what happens when the magnet passes the switch again?