Hey guys,
I have a school project where I have to create an Arduino signal monitor and input conditioner. The details are outlined in the attachment below. Just wondering how I would go about creating a circuit that meets the specified requirements. Any sort of general guidance would be appreciated.
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Get yourself an op amp cookbook. There are simple op amp circuits to do all that stuff.
The spec needs clarification. There is no provision for the LEDs turning OFF once an "alarm" condition arises. Nor can any circuit know if the signal will always be in a particular range.
I've OCR'ed it (below) so it can be referred to.
Input Monitor
Design a circuit that accepts at its input a periodic (but not necessarily time harmonic) signal
ranging in magnitude from -9V to +9V with frequency components ranging from DC through
5000 Hz.
Your circuit should illuminate a green LED if the amplitude of the input signal is always in the safe range for observation by an Arduino Uno (from 0V to 5V).
If the input signal is not always in the safe range a warning should be produced.
The warning should consist of:
a single red LED being illuminated if the magnitude of the input signal ever exceeds 5V,
a single amber LED should illuminate if the magnitude of the input signal ever drops below 0V, and
both the red and the amber LEDs should illuminate if the input signal both exceeds 5V and falls
below 0V during its period.
Finally, if there are any frequency components in the signal that are above 250 Hz then a blue LED should illuminate.
Signal Conditioner
Design a circuit that accepts at its input a periodic (but not necessarily time harmonic) signal
ranging in magnitude from -9V to +9V with frequency components ranging from DC through
2500 Hz. Your circuit should ‘condition’ the input signal by modifying it in such a way that all
the frequency components below 150 Hz are preserved and the relative amplitudes of all
frequency components below 150 Hz are maintained. The output of this circuit should be
appropriate for observation by an Arduino Uno (from 0V to 5V) and provide for as much
dynamic range as possible.
Really ? Come on !
That's a text book "window comparator circuit - Search"
"window comparator circuit - Bing"
The only changeS you need to make the +Vcc needs to be +9Vdc and the -Vcc needs to be -9Vdc , which requres use of a bi-bolar supply instead of a single ended supply.
Also, you might want to use rail to rail op amps like the LTC1637
Hi,
Where does it say you need to use a microcontroller?
What class is this for?
It sounds like an analog electronics question.
Tom.... 
Not to be stuffy or anything but isn't the goal for you to learn not for us to get a get a good grade. Having said that I would assume prior to this project the instructor taught you some basic building blocks. For us (me) to help it would be best if you could tell us what circuits you have learned.
Not to be stuffy or anything but isn't the goal for you to learn not for us to get a get a good grade
Speak for yourself. I want a grade.
raschemmel:
Really ? Come on !
That's a text book "window comparator circuit - Search""window comparator circuit - Search"
The only changeS you need to make the +Vcc needs to be +9Vdc and the -Vcc needs to be -9Vdc , which requres use of a bi-bolar supply instead of a single ended supply.
Also, you might want to use rail to rail op amps like the LTC1637
Hey raschemmel,
Thanks for your input!! I was already under the impression that a window comparator would be the best approach to the the problem. I was thinking we could use a window comparator similar to the second link you posted but with an active LPF on the output. Let me know if this would be a reasonable approach to the problem as I have only been learning about Op-Amps for a couple of weeks and have yet to develop a full understanding of the concepts.
Thanks
Before you jump in and start messing around with window comparators you need to understand that which pin the Vref is connected determines whether the pulse is generated when the input is increasing or when it is decreasing.
Comparators, as opposed to OP AMPS are open collector, , so you can connect as many comparators you want to
the same output with a single pullup resistor and each detector will generate it's own pulse based on the input
signal, but all the pulses will be in the same waveform (pulse-1, pulse-2 , pulse-3 etc)