Need help with Photocell design

Thread Starter

Photocell213

Joined Jul 30, 2021
6
I am trying to create a small (easy to hide) unit which will sense a flash of LED light in any outdoor setting. The goal is to send or remove a 12 volt signal to a timer whenever it detects a Flash of light.

The product will need to be able to detect the flash in all outdoor settings (Sunny clear sky, Dusk, and Dark Night). Is it possible to do this using a photocell? Won't the photocell be held open during changing sky conditions?
 

MrChips

Joined Oct 2, 2009
24,189
Welcome to AAC!

Think of how a TV remote controller works and is not responsive to other interference.

1) It uses IR detector that is covered in a dark material that is opaque to visible light.

2) The emitted IR signal is modulated at 38kHz so that it is unaffected by continuous IR.

3) The signal is encoded with a checksum to make it immune to random noise.
 

Thread Starter

Photocell213

Joined Jul 30, 2021
6
Welcome to AAC!

Think of how a TV remote controller works and is not responsive to other interference.

1) It uses IR detector that is covered in a dark material that is opaque to visible light.

2) The emitted IR signal is modulated at 38kHz so that it is unaffected by continuous IR.

3) The signal is encoded with a checksum to make it immune to random noise.

Thank you MrChips! Could you dumb this down for me a little bit? I'm just a beginner in the electronics game, kind of doing it for a hobby.
 

ericgibbs

Joined Jan 29, 2010
13,624
hi 123,
You will find that in 'Sunny' lighting there is sufficient IR to saturate the IR detector.
Pulsed or continuos.

We need much more information
E
 

MrChips

Joined Oct 2, 2009
24,189
This is what a Panasonic PNA4602M IR detector looks like.

Panasonic PNA4602M
1 - Signal
2 - GND
3 - +5V
1627653547945.png

The signal transmitted and received might look like this:

1627653670357.png
 

MrChips

Joined Oct 2, 2009
24,189
To Trigger a 12 volt signal when the light activates
You told us that already.
Why do you want to trigger a 12 volt signal?
What causes the light?
What is the purpose of all of this?
Is this a game or a commercial invention, for example a garage door opener?
Why are you so secretive about this?
 

LowQCab

Joined Nov 6, 2012
1,096
No he's building a "Christmas-Tree-Sensor" for Drag-Racing.
For those of You not familiar with Drag-Racing ........
There is a pole at the Starting-Line with a series of lights that create a "Count-Down" to Green.
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What you need to do is mount a Low-Power Rifle-Scope on your Dash which will
concentrate the Light coming from the "Christmas-Tree" into
an LED which is the same Color as the LEDs on the Christmas-Tree.
An LED will act as a Photo-Detector also,
and the Color of the Light that it is designed to emit
is the Color of Light that it is also the most sensitive to when used as a Photo-Detector.

So, You want a Yellow-LED to use as a Photo-Detector for another Yellow LED Light.

The change in Current is pretty weak,
so it will need substantial amplification,
a MOSFET Transistor, or a JFET-Input-Op-Amp will be required,
with a concentrating Lens,
to create a reliable signal.

Everything You need to know is contained in the attached *.Doc
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Attachments

LowQCab

Joined Nov 6, 2012
1,096
No matter how You do this, experimentation is going to be required.

First the Optical part ........
You need to find a way to concentrate the Light coming from the Bulb You want to detect,
and block-out Light coming from any other source,
especially outside Light that is the same Color, or "White"-Light.

If You use any type of Lens arrangement to do this,
the LED must be placed exactly at the focal-point of the Lens,
which may change slightly depending upon the average distance from the Light-Source.

Once this is accomplished,
it's time to document the sensitivity of the particular LED that You have chosen.
This can be done by measuring the Voltage that the LED generates when the Light is "On",
verses the Voltage that the LED produces with only ambient Light.

The LED is only capable of producing a very tiny amount of Current,
but the Voltage may actually be surprising.
For this reason, a good Digital-Multi-Meter must be used,
which does not present a significant Load to the LED.

Putting additional, identical, LEDs in parallel will increase the available Current,
and may be required to make this project feasible.

There is a remote chance that the LED(s) put out a definite, repeatable, Voltage,
so much so that a High Value Resistor would be a bonus to "Load-Down" the Output.
But, most likely, you'll have to fight and fiddle with this arrangement to get a usable result.

An Op-Amp, set up as a Voltage-Comparitor will be required to "amplify" the "Signal".
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Tree Trigger 1 Flat .png
 
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