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help regarding hw to detect the changes in analog signals using MC


Moderators: Ajay, Junied , abbas1707, Arun Kumar V, pdi33, Shailesh NAYAK, ۞ TPS ۞, shyam, sashijoseph

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anjel

Mon Aug 18 2008, 12:45AM

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hey!!
i m working on a project titled "EOG based wheelchair direction control"
we have acquired the EOG signals.these signals are in the form of a +ve and -ve pulse when looking left and right.so my application is to turn the wheelchair in left direction on a +ve pulse and in right direction on acquiring a -ve pulse. My problem is " how does the microcontroller recognize and differentiate between +ve and -ve pulse" as we futher have to interface the respectine motors of the wheels and control its speed using controllers.We havn't studied controllers as a subject and it is all self-study that i m doing.
i have worked on 2 ideas:
1.) using a comparator to detect the +ve or the -ve pulse and give it directly as a trigger interrupt to controller and then do the programming and m confused here.
2.) using ADC to interface with microcontroller. Now here the problem arises as i don't kw the slightest to use ADC.
i have read theoritically as hw to use to use ADC bt m not clear as in my application.

CUD U PLZ HELP ME OUT!!!! AWAITING REPLIES.......

pdi33

Mon Aug 18 2008, 06:25AM

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Hi anjel,
if the input pulses are digital in nature, i.e. if the pulses attain a discrete +ve/-ve level, then u do not need a ADC for the job. The simplest way would be to give the signal to the base of a NPN transistor ( to sense the +ve signal) and a PNP transistor ( to sense the -ve pulse) and connect the output of these transistors to two ports/ interrupts of the uC.
here is a possible circuit. values of resistor depend upon the voltage level of the input.

edit:
the correction rightly pointed out by SJ has been done and posted later in this thread.

[ Edited Thu Aug 21 2008, 11:17AM ]

* inspired to develop,developing to inspire *

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anjel

sashijoseph

Tue Aug 19 2008, 11:23AM

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If the input signal is TTL,you could directly connect the +ve pulse through a 10k current limiting resistor to a port pin and the -ve pulse through the pnp inverter as suggested by Pdi above.

Let there be music........

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anjel

anjel

Wed Aug 20 2008, 10:15PM

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Thanks for reply!!!!

We never thought of this approach!!!!
One more doubt regarding interrupts.......

which kind of interrupt to use here??

A lot many regards to u guys!!! My problem has been solved to great extent!!

sashijoseph

Wed Aug 20 2008, 11:40PM

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You'll have to use external interrupts(P3.2 and P3.3).Edge triggered would be better.
Use the ckt provided by Pdi(both transistors) if using interrupts.

@Pdi ... plz edit the pnp ckt and connect the output to the emiiter(it's now tied to Vcc!!)

Let there be music........

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anjel , pdi33

anjel

Thu Aug 21 2008, 03:19AM

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one more thing ......the problem with our signals is that being a biological signal(EOG), it will have a considerable amount of noise.....so won't the transistors detect +ve of noise as input signal. Though the difference between noise +ve and signal +ve is large enough. And wt kind of transistor have we to use e.g:BC547 etc.....