Re: Need help with intermittent circuit failures - JK Flip Flops
- From: "petrus bitbyter" <pieterkraltlaatditweg@xxxxxxxxxxxxxxxxx>
- Date: Wed, 7 Jun 2006 17:03:48 +0200
"Jason S" <jst3712@xxxxxxxxxxxxxx> schreef in bericht
news:44857b20$1_1@xxxxxxxxxxxxxxxxxxxxxx
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.
Jason,
I have a real problem in understanding the details of your circuit.
(Although I understand very well what you want to achieve.) You can sent the
..JPEG to my address but you will have to remove the spamtrap which is in
Dutch: laatditweg(at)enditook means: leavethisout(at)andthistoo.
Meanwhile, the faults you describe are often caused by bad construction.
Wires too long, no or insufficient decoupling, bad solderjoints and so on.
Nothing to blame you. I learned it the hard way.
Why do you need a JK flipflop? A D-type will do the same job unless you've
something in your circuit I don't know about.
Do you switch the polarity change-over and the power relay at he same time?
May cause problems as electric current tend to be much faster than
electromagnetic switches i.e. relay. :) I'd power the motor let's say 50ms
after the switching of the change-over.
One of the programs to draw ASCII circuits can be found:
www.tech-chat.de
petrus bitbyter
.
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