drive circuit for IR sensor

[baftab]

hey
i am working on a project and i need to connect at89c51 interrupt to an ir sensor

my ir sensor has an output of 2 v, when its nc
when its broken, its output goes to .8v

i cannot drive my controller with 2v, so made a drive circuit
i havent yet connected it to my controller
here is the schematic...tell me...is it enuff to convert 2v to 5 v??

thanks

 

[ericgibbs]

hi,
As the signal Vmax is only 2.1V and the Vbe junction of the transistor is about 0.7V, this means the 10K series resistor has only 1.4V across it.
This gives a base current of only 0.14mA!, if the transistor has a gain of 100,the transistor will only have a collector current
in the order of 14mA, which is too low to drive a relay.

I would reduce the 10K resistor to a value of about 330R.

What is the purpose of the relay in the IR sensor circuit,
[do not connect as relay to a MCU as you have drawn it, the back emf could damage the MCU]

It would be possible to connect a 4K7 resistor in place of the relay and use the transistor collector out of 0V/+5V to drive
the MCU pin.
[the signal would be inverted, but this should be easy to correct in the program].

 

[baftab]

oh am sorry...i am not connecting a relay...
i was thinking of directly connecting the output to the mcu....the two wires tht say "to microcontroller"

i dont intend to drive a relay...wrote it wrongly in the title...

i'll change the base resistor , but the collector resistor is fine..right??
i dont intend to use a relay

is there anything else wrong??

 

[ericgibbs]

oh am sorry...i am not connecting a relay...
i was thinking of directly connecting the output to the mcu....the two wires tht say "to microcontroller"

i dont intend to drive a relay...wrote it wrongly in the title...

i'll change the base resistor , but the collector resistor is fine..right??
i dont intend to use a relay

is there anything else wrong??

Hi,
The collector resistor is OK.
I see from your drawing that you have +6V to the top of the resistor, will your MCU accept a +6V input! or does it specify a maximum of +5V?

 

[ericgibbs]

hi,
The 10K will limit the input to the MCU pin to +5V.

 

[baftab]

thanks a lot

 

[baftab]

one thing more
using uln2803...will it work?
i mean instead of a frive circuit...can i use uln2803???

 

[kasungayantha]

dear sir,
can u send me remote controller circuit for control two relayas !!
please reply me soon as possible (kasungayantha@yahoo.com)

thankyou !!