Probably a simple question, but...

I want to have a motor started by tripping a relay when someone breaks
a beam of light (dark activated relay). I then want to power to the
motor to cut when it makes one revolution by tripping a rocker switch
or something similiar, which would cut the power (close the relay). I
already have the circuitry for the beam of light relay.

I initially thought a second relay, between the light relay and the
motor would do it, but I cannot think how to wire it up where the
middle relay stays on. Wouldn't it just open and close real quick as
the light relay opens and closes?

What do I need to do to have the dark activated relay activate another
relay that stays on and runs my motor, then allows my motor to turn the
middle relay off when the motor trips a rocker switch upon one
revolution?

 

Nowadays, with small, cheap microcontrollers so available something like
this might be easier to throw together as a digital system rather than
with relay logic. However ...

\_
/
v
| .-. |
o---------( L )----------------------o
| '-' |
| . |
| . |
| . |
| L1| | KA .-. |
o-o--------| |---------o---( K )-----o
| | | | | '-' |
| | | . |
| | | . |
| | | . |
| | B1 | . |
| | | |/ A1| | | . |
| '--|/|----------| |--' . |
| /| | | | . |
| . . . |
| . ........... |
| . . |
| . . |
| . A2| | .-. |
o-----------------| |------( M )-----o
| . | | '-' |
| . . |
| . . |
| . . |
| . . |
| . . |
| KB.-. M1| | |
'---( K )-------------------| |------'
'-' | |
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)


1. An event at light sensor L shuts L1, energizing KA.
2. KA shuts sustaining relay A1 and motor power relay A2.
3. When the motor reaches the end of its travel, it shuts M1.
4. M1 energizes KB which opens B1, turning off KA.
5. When KA is de-energized, A2 opens, turning off motor M.

This assumes that the motor is in the active zone holding KB energized
long enough to drop KA, and that the motor coasts through far enough
after being turned off to release KB at the end of travel. Otherwise,
use a timer for KB with a fixed "on" state time.

If the light sensor stays active, KA stays energized and the motor keeps
running, which may or may not be desirable depending on the actual
application.

Personally, I'd use something like an ATtiny11 (8 pins, internal
oscillator, priced at $0.54 qty one at Digikey) with the light sensor,
one microswitch at the motor, and one relay for the motor power.

 

---
Use the output from the beam-break detector to fire a one-shot which
sets a latching relay (or an RS latch) which drives the motor-run
relay.

Use the output from the motor switch to fire another one-shot which
resets the latch, de-energizes the motor-run relay and stops the
motor.

Tell us what kind of voltage and current the motor needs to run on,
what the beam break relay and the motor switch look like, and I'll
draw you a schematic if you want one.

 

Rich - no question that a microcontroller would be the way to go as I
understand that logic better than going the electronic relay route. I
do a lot of programming in my job and having an output be triggered by
an input is much easier for me to wrap my head around. Unfortunately, I
do not have the time to get all the pieces, learn how to use it and
then learn how to implement it. After this project is over I will begin
learning how to use microcontrollers. I have never heard of the
ATtiny11 (really just the PIC series microcontrollers), but will being
looking into this soon. Thanks a lot for the reply.

John - I had not heard of a latching relay. This appears to be exactly
what I am looking for. I knew that I probably needed some kind of
elecronic switch that stayed in it's last position, but didn't know
what to look for. Would I need an "impulse relay" to do this? Is this
something I can get from Radio Shack?

Everything will be 12V. I planned on building the dark activated relay
like the one on the left side of the page here:

http://www.uoguelph.ca/~antoon/circ/actrelay.htm

only with using parts rated at 12V. I was just going to use a rocker
switch to turn off the current from the motor. Is there a better idea
than using a rocker switch? I planned on the motor just spinning around
and having it hit the rocker upon one complete revolution. If there's a
better way here let me know.

 

What if the light switch applied power for a period of time (say 60
seconds using a capacitor)?

How would I get this to work:

The motor gets power and turns. When it does 1 revolution, it hits a
switch (SW1).

The SW1 closes, it activates a relay (R1) that cuts power to the motor.
As long as power is coming from the light switch, R1 keeps cutting
power to the motor. When power is cut after 60 seconds, R1 goes back
and once again allows power to the motor when it is triggered.

Would this work? If so, can someone draw it up - I can't seem to make
sense of it.

 

Jamie - The message I posted immediately after your first reply was
done before I read your first message. I think we are thinking the same
thing though. Could you do a simple schematic so I could get a visual?
Just the part after the light switch.

 

---
There is a better way. The detector circuit shown doesn't have a
clearly defined switching point and should be designed around a
comparator. I don't know, physically, how you plan to mount the
rocker switch, but unless the motor continues past the point where
the switch cuts the motor off and returns the switch to the ON
position, you'll never be able to start the thing again!

The solution there is to use the one-shots and latch I recommended
earlier since the stop and start aren't dependent on each other.
I'll post a schematic for you on abse sometime today.

 

to make your job easier since it looks like your looking for a simple
solution.
use the optical method as you are now to hold on a relay.
use a normally closed proximity switch that would hold a control lock
loop closed on this same relay when the sensor is not being tripped.
the idea is to position the optical in such a way that it will say on
long enough to get the motor rotating enough to move the index away from
the proximity switch so that it will complete the lock loop control line
which will hold the relay on until the rotor comes all the way around
and trips it once again to open the lock loop.

basically a double pole relay is needed here, one pole to start your
motor and the other pole use to create a loop lock.
the magnetic switch will break the loop when it's on target.
just remember that the optical must be position so that is will say on
long enough to get the magnetic off target so that the loop will be closed.
actually, you could use magnetics on both sections..
you could also use a flip flip and use only 1 sensor..

 

Just have the rocker switch cut the power to the whole circuit.

or do you one it to start again next time the beam is broken?


Bye.
Jasen

 

--
have the light switch start a one shot timer relay that
will energize the main relay for the motor.
have the stop switch also loop around from the 120 control
line source to directly energize the main relay..
by the time the one shot timer has expired, the motor shaft
will be well out of the position of the light switch and the
stop switch will be off it's stop position in the close state
keeping control power to the main relay coil.
when the switch hits the stop position again, it will simply
open up and thus turn off the main relay for the motor.
like i said before, you can do it with out a one shot timer
if you simply position the light switch so that what ever
trips it will stay in view long enough for the motor to turn enough
to get the stop switch in the close position.


Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

To do it the way you mentioned, you need a double pole relay in
addition to your existing beam of light relay, plus the rocker
switch (or whatever) you mentioned.

I'll assume 12 volts for the circuit below. RY1 is your existing
beam of light relay.

RY1 Contact
/
+12 ---+---o o----------------+---[RY2]--- Gnd
| |
| o
| / /
+---o o--------------o
RY2 Contact #1 Rocker Switch


RY2 Contact #2
o-------------- to motor
/
o
|
+---------------- to motor

How it works: When RY1 (beam of light relay) energizes, the
contact closes and RY2 is energized. RY2 contact #1 provides
a path for 12 volts to reach the RY2 coil, through the rocker
switch, to keep RY2 energized even after RY1 is no longer
energized. RY2 contact #2 is used to complete the circuit
to the motor. When the motor spins and activates the rocker
switch, the path to RY2 is interrupted, RY2 denergizes, and
the motor is turnrd off.

RY2 is a double pole relay, chosen for a contact rating that
can handle your motor's rating.

Ed

 

neither can I. try this.

----+--+------+--------------------+------------- +12
| | | ||+ | .
| | +--[R1]----+----||---+ .
| | | ||C1 .
SW2 | | SW1 | o .
| o | |-| .
|-| | | o o-----.
| o | _-~ | _-~ |
| `--~. o----------)-----~. o--. |
| . | . | +----.
+-----+-. +-----+-. | | |
| | |RY1 | | |RY2 | | |
| | | | | | | | |~|
| | | | | | | | /~~~\
| .--+-' | .--+-' | | |motor|
| | | | | | | |
| | +--)---------' | \___/
| | D1 | | |_|
`--)---------|<---------)------------+ |
| | |
------+--------------------+-----------------+--- ground

sw2 is your light (dark) sensor when it closes relay one energises
while relay 1 is energised current flows through its contacts and through
relay2's contacts to run the motor, should switch 2 be released current also
flows through the diode D1 maintaining relay 1 in the on state.

when the motor has done a full rotation it closes SW1

current flows through the capacitor and closes relay2 this breaks the
circuit feeding power to the motor which stops and if SW2 is now open
there is no source of current to energise RY1 which opens

if SW2 is still held closed current flows through the ry1 contacts and the
now closed RY2 contacts and maintains RY2 in a closed state until SW2 is
released and RY1 opens

When RY1 opens the power is cut to RY2 which opens
immediately in the case where the motor has progressed slightly past SW1
before halting or after C1 has charged up in the case where SW1 is still
closed

for motors upto 15A automotive headlight (RY1) and horn (RY2) relays
may be suitable

D1 can be any GP rectifier diode (eg 1N4001)

if R(ry2) is the resistance of the relay 2 relay coil.
R1 should be about 10 times R(Ry2)
and C1 should be about 10000/R(Ry2) microfarads

for SW1 a microswitch with a roller on its actuator arm would be a good
choice.

 

Would using a cam on the motor to operate micro switches do the trick?

David

 

That's pretty much how windshield wipers work, at least on older cars.
A switch kept applying power to the motor until the cycle was completed.
I have no idea what they do now, prolly pretty much the same thing.