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How to use .5 volts signal ?

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Q411

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Hello , this is my first post I know the basics but am not an electronician ,
more of a handyman .

Here is what I want to do :

My door opener has a magic eye ,when the car is clearing the path of the infrared sensor ,
a tiny led comes out faintly illuminated . The led is hard to see .

The led is illuminated by .5 volt ( half a volt) thus few milliamps

Can I use this tiny voltage to trigger a bigger source of light .

The lowest relay I found is 3.5 volts ...



Thanks , Robert
 
The led is illuminated by .5 volt ( half a volt) thus few milliamps
I think that's extremely unlikely. What did you measure it with? A LED normally needs at least ~ 1.5V before you get any significant brightness. But yes, you could use the LED voltage (or current) to control a transistor which in turn controls a relay or turns on a brighter light. Avoid a relay if you can; it wastes current and its contacts could corrode in a garage environment.
 
alec,
Its possible the OP is measuring a pulsating drive to the LED, using a DC meter,so he reads 0.5v.
 
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Agreed, Eric. Using a low-impedance meter could also drag the measured volts down.
 
Agreed, Eric. Using a low-impedance meter could also drag the measured volts down.

Thanks to all.

I measure with a TES 2712.
There is no ac voltage , it is dc. The led is the very tiny type.View attachment 60195

When the infrared ray is not blocked : voltage .467 ( led is on )(the car clears the door)
when blocked the voltage goes up to .5 (led is off)
To help me see the led I installed a black background.

I have on hand a pnp transistor but dont know the ''montage'' to be done.
I was thinking to use 4 volts dc supply to light up a bank of leds.

Thanks.
 
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When the infrared ray is not blocked : voltage .467 ( led is on )(the car clears the door)
when blocked the voltage goes up to .5 (led is off)
That does not sound right. what is the model number of the sensor assy?

As said before most LEDs have a forward voltage of 1.2 volts or more. They can not be made to work off a lower voltage.
You are saying the LED has more voltage when its off than it does on. Try switching your meter leads around and see what the voltage is.
And yes most door opener magic eyes run off AC.
 
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That does not sound right. what is the model number of the sensor assy?

As said before most LEDs have a forward voltage of 1.2 volts or more. They can not be made to work off a lower voltage.
You are saying the LED has more voltage when its off than it does on. Try switching your meter leads around and see what the voltage is.
And yes most door opener magic eyes run off AC.

You are so right .

I removed the led and checked the wires (set 2):
.94 volt AC is present when the sensor received the ray (car clears the path).
When the sensor is blocked : drop to zero volt.

There are 2 sets of wires : set 1 is supplying 6 volts to operate the sensor.
: set 2 is the status led , which I want to use.

So I have a differential of .94 volt ac

Could I prank open the sensor and change some resistance that would let more juice
to the led ?

Thanks.
 
I have a safety sensor here but its not the same brand.
Can you open yours and take a picture of the parts on the board?
Also if you can take a pic of the back of the board.
I need to know the part numbers on the parts please list them.
I an shore we can come up with something.
Andy
 
You could just use the 6V supply (rectified if necessary) as the supply for a simple npn-transistor switch. Connect a LED or two in series with a current-limiting resistor in the collector path. Ground the emitter. Use the .94V AC signal to drive the transistor base via 470 Ohms.
 
You could just use the 6V supply (rectified if necessary) as the supply for a simple npn-transistor switch. Connect a LED or two in series with a current-limiting resistor in the collector path. Ground the emitter. Use the .94V AC signal to drive the transistor base via 470 Ohms.

alec; He may already have enough power to light more LEDs. Thats why I want to see the parts inside the sensor.
 
The middle pic seems to be different. It has a different back ground and no green LED. Is the green LED there now?
Can you get a better pic of the bottom of the board?
 
The middle pic seems to be different. It has a different back ground and no green LED. Is the green LED there now?
Can you get a better pic of the bottom of the board?

You are right , I change the background to obtain a better pic.

When I installed the red led , I did not remove the original green led just cut one leg ...but
now I removed it definitively.

I set the cam to higher resolution tell me if better is needed , will take wife's cam .
View attachment 60228
View attachment 60229
 
What is the number on the three leged part (transistor) under where the brown wire is soldered to the board.
 
As far as I can tell that is a MMBT2907 transistor good for 800ma. So all you may have to do is change a resister.
Now there needs to be a current limiting resister between the transistor and the led. Looks like the lower one left of the transistor. Can you follow the tracks on the board from the center single lead on the bottom of the transistor to a resister and from the other side of the resister to the LED?
 
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As far as I can tell that is a MMBT2907 transistor good for 800ma. So all you may have to do is change a resister.
Now there needs to be a current limiting resister between the transistor and the led. Looks like the lower one left of the transistor. Can you follow the tracks on the board from the center single lead on the bottom of the transistor to a resister and from the other side of the resister to the LED?

Tomorrow I will study your advice and see if i undestand well , i had to re-install the sensor otherwise the door become
inoperable .

Thanks.
 
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As far as I can tell that is a MMBT2907 transistor good for 800ma. So all you may have to do is change a resister.
Now there needs to be a current limiting resister between the transistor and the led. Looks like the lower one left of the transistor. Can you follow the tracks on the board from the center single lead on the bottom of the transistor to a resister and from the other side of the resister to the LED?

Thanks for taking the time .
Here are the resistors list.
View attachment 60262

Can you tell me which resistor should be changed and the mounting of the led.

Thanks.
 
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