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Offline ManojkumarsmksTopic starter

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ir sensors
« on: August 30, 2010, 12:22:06 AM »
i have built a sensors as given in the following link

http://www.societyofrobots.com/schematics_infraredemitdet.shtml

i have not connected  lm358 ckt,
i want the output of T1(as in first diagram) to be given to MUC 8051 but  the output is analog one..
how do i get the digital output???
to give the output of L1 and T1 to comparator, the output measures around 1.8v!!
please help... please

Offline ballbreaker

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Re: ir sensors
« Reply #1 on: August 30, 2010, 01:35:34 AM »
am not an expert and maybe am wrong but i think in order to get a digital signal you are gonna need to connect a uf ceramic capacitor to filter the analog signal to digital
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Offline waltr

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Re: ir sensors
« Reply #2 on: August 30, 2010, 09:43:30 AM »
Try thinking a a digital signal as really being a analog signal that is either almost 0V (a low) or almost at Vcc (5V) (a high). So there are a few ways to get the output from the photo-transistor to be either a low or high logic levels.
1- addition amplification that swings the full voltage range, 0 to 5V and what the light from the LED reflects from, black or white but not in the greys.
2- Use a comparator IC, the LM339 is a common one, to threshold the input voltage to a low or high logic level.
3- Use a logic gate that has a Schmidt trigger input like a 7414 IC (this is the generic part number so a real part will have a prefix and some letter between the 74 and the 14).

Offline ManojkumarsmksTopic starter

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Re: ir sensors
« Reply #3 on: August 30, 2010, 11:56:46 AM »
hey thanks..will tryout it by 2moro and let u know guys..
thanks a lot...never though ppl will reply!!!
thank u..

Offline Soeren

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Re: ir sensors
« Reply #4 on: August 30, 2010, 05:46:15 PM »
Hi,

i have not connected  lm358 ckt,
i want the output of T1(as in first diagram) to be given to MUC 8051 but  the output is analog one..
how do i get the digital output???
to give the output of L1 and T1 to comparator, the output measures around 1.8v!!
please help... please
There's no LM358 in the first schematic, which is a purely analog circuit and will be best suited for an A/D-input.
No matter how much gain you add, there will always be a range where you have an analog transition.
As waltr mentioned, digital is merely analog driven to the extremes.

The op-amp circuit is also best suited for an A/D-input, but could be changed relatively easy (move the feedback resistor) to give a digital output, just change the negative feedback to be a positive feedback an adjust the value for a sensible shift point. That way the output signal will be either "1" or "0".

If you want to stay with transistors, let the photo transistor control a 2-transistor Schmitt-trigger  and you will get approximately the same functionality.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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