Need help understanding how to use opto-isolator

M

mjohnson

Guest
I want to build an automatic garage door closer with an alarm clock and
my garage door remote. I realize that I could just buy something but I
want to build it so I can learn something and have some fun (and
frustration).

Here is a block diagram of what I am imagining:
http://img98.echo.cx/img98/3411/phase12nt.jpg

My question is what do I need to do to take the output voltage at the
clock's buzzer to activate the interface circuit. The voltage I read
on the buzzer when it's going off is 395mV (.395V). If for example, I
just want to turn on an LED (baby steps right) what would I need to do
to couple the alarm clock to the LED circuit?

I'm assuming that the actual coupling of the LED circuit to the buzzer
will represent a new load to the alarm clock which it wasn't designed
to take. So my guess is that I would need an opto-isolator and run the
LED circuit on it's own power supply? But is 395mV is enough to drive
the opto-isolator?

thanks for your time and help!
 
On 21 Apr 2005 05:17:35 -0700, "mjohnson" <crvmp3@hotmail.com> wrote:

I want to build an automatic garage door closer with an alarm clock and
my garage door remote. I realize that I could just buy something but I
want to build it so I can learn something and have some fun (and
frustration).

Here is a block diagram of what I am imagining:
http://img98.echo.cx/img98/3411/phase12nt.jpg

My question is what do I need to do to take the output voltage at the
clock's buzzer to activate the interface circuit. The voltage I read
on the buzzer when it's going off is 395mV (.395V). If for example, I
just want to turn on an LED (baby steps right) what would I need to do
to couple the alarm clock to the LED circuit?

I'm assuming that the actual coupling of the LED circuit to the buzzer
will represent a new load to the alarm clock which it wasn't designed
to take. So my guess is that I would need an opto-isolator and run the
LED circuit on it's own power supply? But is 395mV is enough to drive
the opto-isolator?
Click to expand...
---
I posted a circuit to another thread, (a ircuit to swith a relay by
alarm clock) which might work for you with a few modifications, so
could you post some more information about your system? Specifically,
on your remote control are the OPEN and CLOSE functions separate or
does a single button toggle them?

What supply voltages do you have to work with?

Do you need the output which is going to the remote to stay on for as
long as the alarm clock provides an output or do you just need a
pulse? If a pulse, how long a pulse?

Could you post some information as to what you used to measure the
395mV and how you went about it? That is, was it an AC or DC meter?
Did you measure the voltage across the buzzer, or from one of its
terminals to ground?

I'm assuming that you're planning on paralleling the contacts on the
remote's keypad with whatever will be actuating it. Am I right?

--
John Fields
Professional Circuit Designer
 
Specifically, on your remote control are the OPEN and CLOSE functions
separate or does a single button toggle them?
Click to expand...

It's a toggle switch, I need it "pressed" for a little less than a
second for it to activate the garage door then I have to let it go or
else the motor won't respond. So I would imagine I need a pluse that
last about 800 to 900 milliseconds.

The alarm clock runs off 3V DC. I measured the DC voltage with a
multimeter between the two solder points on the buzzer itself -- so it
was across the buzzer. Should I be measuring it someplace else?

I'm assuming that you're planning on paralleling the contacts on the
remote's keypad with whatever will be actuating it. Am I right?
Click to expand...

I wanted to extend two leads from the solder points on the buzzer to an
opto-isolator which would activate the "pulse" to the garage door
remote through an intermediate circuit.

Here's a new diagram, as well as front/back images of the remote.

http://img195.echo.cx/img195/4791/diagram6yf.jpg

Front side of the remote:
http://img195.echo.cx/img195/1594/remotefront5nd.jpg

Back side of the remote (red lines are show the traces)
http://img195.echo.cx/img195/6156/remoteback8tt.jpg

I'm having a hard time getting a for the voltage accross the toggle
switch on the remote. I read 0 no matter if the switch is toggled or
not. I am probably not laying my probes across the switch correctly.
Do I need to touch both pairs of connectors at the same time?

I'm assuming that I would use an opto-isolator to interface the pluse
circuit to the remote and that the output of the opto-isolator will be
enough to activiate the remote? I guess I'll just have to try it an
see.

I was going to use an 4N27 opto-isolator
(www.vishay.com/document/83519/83519.pdf) between the clock and between
the remote.

thanks again, let me know if y'all have any thoughts or questions...
 
The alarm clock is powered by two AAA batteries and has a piezo buzzer
so I don't think there's any AC involved.
 
I guess I'm not sure how to measure the AC then. My multimeter has an
ACV seeting for 200 and 750. I might not understand how to use the
meter. Is that what what I use to measure the VC and do I measure it
across at the two leads attached to the buzzer?

Sorry for my ignorance...
 
Ok, I tried using the diode but I think my multimeter isn't fast enough
to sample the data but I did see values ranging from 800mV to 1V this
time (actually, I would see it ramp up from 80mV to generally topping
out at 800mV, 900mV, and 1V).

What do you think? Does ~1V sound like a reasonable voltage across the
buzzer? Are there any other tests I should try? I probably should
invest in an analog multimeter. Is this where SWAG comes into play?

thanks again!
 
I was going to use an optical sensor to determine if the door was up or
down so the device would be very close to the door. The garage door
button is opposite from the door itself so it wouldn't be very close
(13' away). Anyway, this project is just for fun. I just want to do it
as an experiment to learn something from the whole process. Like I
said I could go buy something but the goal isn't to solve a problem
it's just for exploratory purposes.
 
I was thinking that I was just going to have an LED/Detector as the
sensor which is coupled to the logic circuit with an AND gate. So when
the detector is sensing the door in the up position and the buzzer is
going off then pulse a signal to garage door remote.

Here's is an extremely high level diagram (i realize the AND function
is more involved than what is represented).

+----------------+
[BUZZER]->|---\ |
| ON \ |(activatation pulse)
| AND---[555]---|-------------------->[REMOTE]
| UP / oneshot |
[SENSOR]->|---/ |
+----------------+
LOGIC CIRCUIT
 
On 27 Apr 2005 09:39:37 -0700, "mjohnson" <crvmp3@hotmail.com> wrote:

I was thinking that I was just going to have an LED/Detector as the
sensor which is coupled to the logic circuit with an AND gate. So when
the detector is sensing the door in the up position and the buzzer is
going off then pulse a signal to garage door remote.

Here's is an extremely high level diagram (i realize the AND function
is more involved than what is represented).

+----------------+
[BUZZER]->|---\ |
| ON \ |(activatation pulse)
| AND---[555]---|-------------------->[REMOTE]
| UP / oneshot |
[SENSOR]->|---/ |
+----------------+
LOGIC CIRCUIT
Click to expand...
---
So if the door is up and the alarm clock goes off, the circuit will
pulse the remote, but if the door is down and the alarm clock goes off
the remote won't be pulsed?

--
John Fields
Professional Circuit Designer
 
Yup... that's the plan for phase 1. Plan for phase 2 (assuming phase 1
ever works) is to add another sensor to determine if there is actually
a car (or movement?) in the garage. If there is no car (or if there is
movement) then the remote won't activate.
 
Wow! thanks for doing drawing up that schematic. That was very kind of
you.

I do have a question, since the buzzer will be buzzing I need to
"absorb" the transitions between the buzzer oscilations. Functionaly,
I just need to know that the buzzer is going off. Is that the reason
for the .1 uF cap between the alarm and the rest of the circuit, to
absorb the oscilation and keep the voltage high for the duration of the
alarm?

thanks!

ps: I have order my components and I'm waiting for them to arrive in
the mail....
 
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