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help with My MCS51 final project


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anewbie

Tue Apr 28 2009, 10:31PM

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i have some project for my final graduation project

can any body help me for:
- project temperature sensing using LM35
- ADC using ADC 0808
- Wireless communication between Uc
- PWM for driving DC motor using L298

those are my final project for my graduation
right now i'm working on those 2 in first list

do you have any schematic diagram for communicating LM 35 with MCS 51 by ADC 0808
i ordered to use a OpAmp tu amplify the temperature range i use LM 741 for the OpAmp

but still i didn't get how should i make the circuit

Ajay Bhargav

Wed Apr 29 2009, 01:32PM

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LM35 gives you o/p at a step change of 10mV/*C
and voltage o/p ranges from 0 for 0* to 1.5V for 150*

now the range you want is.. 0-5V
which means you need to amplify in such a way that 1.5V should come as 5V at o/p.
I hope you know how opamps work, so calculate the R1 & R2 values of resistance in amplifier more to get that much of gain. take help from your opamp book

if you need help do post.

and interfacing of ADC0808 is simple just look into ADC's Datasheet.

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anewbie

anewbie

Wed Apr 29 2009, 10:23PM

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thanks man,
that is geenral problem, now when i try to measure the voltage output of LM 35 i use, 3K ohm in graound, and branch the out put to ground using 200 ohm resistor,

i get the voltage correctly, near 0.278V (at normal temperature 27C)

but when i finish to measure, and unplug all supply, include Power supply and touch the LM 35, it's feel burn, i mean hot, it is normal, or i need to increase the resistance from output to ground?

let say 5K its that okay?

Ajay Bhargav

Thu Apr 30 2009, 05:09AM

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check datasheet of LM35 first page. it better not to ground the o/p use it directly.

or you have to pull down with -VCC instead of ground and resistance is calculated as

R = -VCC/50uA

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