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Questions about 8051 and IR LEDs in a black line follower robot

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blueshift

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I am making a black line follower robor usibg Atmel 89c1 chip and programmed using C under KeilC development s/w. I have the following doubts in it:

1. Why do we use pull-up resistor at port 0 of 8051?

2. We are using 3 pairs or IR Tx and Rx diodes. Are these operated in forward bias or reverse biased?

3. How does it detect black line? Has that got anything to do with wavelength? What is the wavelenth of black color?
 

Re: 8051 and IR LEDs

Please someone reply.
 

Re: 8051 and IR LEDs

please tell me to what the pull up resistor is connected... i mean whether something is connected to the port 0 or just a pull up to the supply is used...

The IR Tx is operated in forward bias and Rx in the reverse bias...


black color is just the absence of all colors and hence it doesn't absorb radiations and hence black line is used.... \]
 

Re: 8051 and IR LEDs

1-port 0 of 89c51,2(or s51,2) is open collector(drain) port.(the collector of internal transistors not connected to supply )
so we must use of external pull up resistor and so this port can supply current more than other ports.
 

Re: 8051 and IR LEDs

use of pullup reg is
for Port 0. Having the "pull up" resistor, Port 1 is fully compatible with TTL circuits.

Added after 2 minutes:

ans 2 : Now we are using the 3 led for sensing the veichle whether going right or left or it is on the track i.e. the black tape of not .
 

Re: 8051 and IR LEDs

Port 0 is open drain / open collector and as such needs to be connected to the supply. This has the advantage of being able to supply more current to the circuit.

Cheers
Slayer
 

Re: 8051 and IR LEDs

it has open drain output so as to interface with external memory..
We need a true bidirectional port for interfacing of memory.. and PORT 0 serves as both data bus ( D0-D7) and lower address bus( A0-A7).. these are time multiplexed
and lower byte of address is latched with the help of an octal latch and ALE signal.
 

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