AVR-Chat

Bi-directional communications with a single LED? Been doing that for years!

However to achieve higher speed as a sensor you really need to operate 
the LED in current mode rather than photo-voltaic mode. This requires 
something as simple as a single NPN and maybe a pull-up resistor in the 
collector if necessary. Usually I use a PNP to drive the LED and an NPN 
to sense it. The I/O pins are usually the UART. This worked perfectly 
fine on an 8535 as well as other processors using IR LEDs at close range 
running at 4800 baud.

Nothing stopping you from using visible LEDs except maybe the 
interference you might get. The IR leds will work fine unless you have 
direct sunlight, in which cas the sensor just saturates.

Additionally, in one case I did double duty with the LED and even 
modulated it to communicate to a HP calculator printer.

I call it my 20 cent wireless coms.

Basic circuit connections:-
GND ~~ [LED- LED+] ~~ 10K ~~ BASE
             LED+] ~~ 100R ~~ OUTPUT PORT   ( or use a PNP for more 
drive or if using a UART )
VDD ~~ PULL-UP ~~ COLLECTOR ~~ INPUT PORT
GND ~~ EMITTER


*Peter*

fjch100 wrote:

>>>fjch100 wrote:
>>>      
>>>
>>>>HI, I just upload a new pdf file with information about using 
>>>>        
>>>>
>>normal 
>>    
>>
>>>>LEDs like sensor to interchange information between modules.
>>>>I just found it surfing the web, but I feel the need to share 
>>>>        
>>>>
>>with all 
>>    
>>
>>>>the AVR comunity. I may be some one can write a driver in GCC 
>>>>        
>>>>
>to 
>  
>
>>just 
>>    
>>
>>>>include and use in all the AVR projects....
>>>>        
>>>>
>>>Wanna tell us the file name?
>>>
>>>erikc
>>>
>>>      
>>>
>>the program name is:
>>
>>Comm_using_Bidirecctional_LEDs.pdf
>>
>>    
>>
>This is the abstrac of the file:
>
>A novel microprocessor interface circuit is described which 
>can alternately emit and detect light using only an LED, 
>two digital I/O pins and a single current limiting resistor.
>
>This technique is first applied to create a smart illumination 
>system that uses a single LED as both light source and sensor. 
>We then present several devices that use an LED as a generic 
>wireless serial data port. 
>
>An important implication of this work is that every LED connected
>to a microprocessor can be thought of as a wireless two-way 
>communication port. 
>
>We present this technology as a solution to the "last centimeter
>problem", because it permits disparate devices to communicate with 
>each other simply and cheaply with minimal design modification.
>  
>