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circuit design

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veenapriya

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Am transmitting a signal serially through LED.Am using a photo diode at the reciever.I want to increase the distance between the transmitter and reciever upto a meter.What are the key considerations for designing the circuit?
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

Here are a few...

1. Power of the LED.
2. Sensitivity of the photo diode.
3. Frequency of the carrier.
4. Selectivity of the receiver.
5. Directivity of the LED and photo diode, lensing.
 

ronsimpson

Well-Known Member
Most Helpful Member
Infrared Receiver:

http://www.mouser.com/ds/2/427/tsop382-531411.pdf
http://www.mouser.com/ds/2/427/tsop48-542449.pdf
http://www.mouser.com/ds/2/427/tssp40-461157.pdf
http://www.mouser.com/ds/2/427/tsop48-542449.pdf

On the TSOP48xx:
Look at what MrAl wrote:
These parts have a lens so they see light only from one direction.
The case is "black" to your eye but it is clear at IR. This removes most of the room light.
They work best if the light is turned on/off at some frequency (carrier) like 38khz.
The data should be of a certain type. pulses for 600uS then no pulses for 600uS.

Spend some time looking at this type of part on the receiver side.
 

MrAl

Well-Known Member
Most Helpful Member

MikeMl

Well-Known Member
Most Helpful Member
Optical Fiber between the LED and the Photodetector (blocks out incidental light)?

This is really tough to do because of incidental illumination due to room lighting or daylight. The only other hope is to modulate the emitter with a "carrier" (like 38kHz), and then build a narrow-pass band "receiver" with lots of ac-coupled gain...
 

ronsimpson

Well-Known Member
Most Helpful Member
Post #2 item 5.
On both the transmitter and receiver.
>On transmitter; focus the light so more power gets to the receiver.
>On receiver; it only needs to see the transmitter. A lens will remove some of the room light.
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

Yes, and a short to long tube with flat black paint in the inside for the receiver to narrow the field of view.
Helps a lot.
 
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