Intro: Simple Light Based Proximity Sensor
This is mostly based on the intensity of light
The intensity(magnitude) always increases with the decrease in distance between the source and the object.
Step 1: Gathering Components
you will need -
1-NE 555 ic.
2-Any output source under 5V (the LED is fantastic).
3- LDR (light dependent resistor)
6-10 K resistor
7-100 µf capacitor
8- 9V power supply
Step 2: Basic Info
-The Light Dependent Resistor aka LDR is a device that I think works on Photo Electric Effect
When light falls on the surface, Electrons are emitted bridging the zig-zag gap.
More the light less the resistance.
-The NE555 IC is timer based -for now just know that it generates electrical pulse
Step 3: PIN OUT's for the 555 Timer IC
(Always remember that the nearest pin to the circle is pin one)
PIN 1- Ground
PIN 2- Trigger
PIN 3- Output
PIN 4- Reset
PIN 5- Control voltage
PIN 6- Threshold
PIN 7- Discharge
PIN 8- Power
note- The pins that we will be requiring are 1,2,3,6,7 and 8.
Step 4: A Voltage Devider
a voltage divider is basically a series of resistors or capacitors which can be tapped at any intermediate point to produce a specific fraction of the voltage applied between its ends.
In the above circuit schematic R1 and R2 are resistors connected in series and a wire is drawn out a from the junction.
Step 5: Connections
1- Place the IC on the bread.
2- Make a positive and a negative rail. (note-in the above picture the top rail is positive and bottom rail is negative.)
3- Connect pin 8 to positive and pin 1 to negative.
4- Connect your output source's positive to pin 3 and negative to the bottom rail.
5- Connect a capacitor from pin 2 to the bottom rail.
6- Connect pin 6 to pin 2.
7- Connect the resistor from pin 8 to pin 7.
8- Connect the LDR from pin 7 to pin 6
Thats mostly it.
Step 6: Why Introduce the Voltage Devider
Notice that there is a voltage divider built in the resistor block.
Here instead of a resistor we installed the LDR in place of R2,which is a variable resistor.
Step 7: What the Output Should Be
The LED should blink really fast in bright light and as the intensity decreases, the on and off time increases
in other words as the light gets dimmer the LED takes a longer time to turn on and off.
(And like I stated in the start "intensity/magnitude increases with decrease in distance between an object and a source")
Step 8: Just Suggesting
Try putting some different value resistors and capacitors to suit you.
It will simply change the on off period's ratio.
To give a little accuracy try making a black duct tape pipe of the same diameter as the LDR and place it on the LDR
That shall narrow down the stream of light falling on the LDR's surface and hence decreasing unwanted interferences.