Re: Need help understanding how to use opto-isolator

On 22 Apr 2005 05:57:14 -0700, "mjohnson" <crvmp3@xxxxxxxxxxx> wrote:

>>Specifically, on your remote control are the OPEN and CLOSE functions
>separate or does a single button toggle them?
>
>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?

---
Across the buzzer should be OK, but 395mV sounds awfully low, so I
suspect it's being driven by AC. Measure it with your meter set to AC
VOLTS and see what you get.
---

>>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?
>
>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.

---
Before anything can happen we need to find out definitively what's
happening at the buzzer when the alarm goes off, or we need to find a
signal somewhere in the clock which changes state when the alarm goes
off. Either that or couple to the clock acoustically in order to
detect the sound of the buzzer and use that to trigger the chain of
events leading to the activation of the remote.
---

>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?

---
No, it looks like you only have to get across the terminals with trace
connected to them. But, since we don't know how the switch is being
used in the circuit, it would be best to use relay contacts (instead
of the out of an optocoupler) across the switch terminals in order to
activate the remote. Test it by shorting the terminals momentarily
and see if it works the door. If it does, then relay contacts will be
fine.
---

>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 wouldn't use an opto because of the current required for its LED and
the uncertainty of being able to use its transistor output to trigger
the remote.

Here's what I see as a much simpler solution, with only the clock
output needing to be defined in order to make it work:

INTERFACE
BATTERY
CLOCK 4.5V REMOTE
BATTERY | BATTERY
3V +---------+---------+ 3V
| | | | |
+--+--+ +--+--+ +--+--+ +--+--+ +--+---+
|CLOCK|---|ALARM|---|1SEC |---|REED |---|REMOTE|
+-----+ | DET | |MONO | |RELAY|---|SWITCH|
+-----+ +-----+ +-----+ +------+


--
John Fields
Professional Circuit Designer
.

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