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Proximity Sensor Based Circuit

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Ergh

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Hello, this is the first time I have used this forum. I was hoping I might be able to get some advice regarding a circuit design. The design specification states there voltage must be clamped to a range of 0v - 3.3v and must use a sensor.

Right, my idea was to use a proximity sensor (Sharp infared upto 30 cm detection) and have 3 conditions. From 30cm to 20cm display a green LED, from 19cm to 10cm display an orange LED, and from 9cm to 0cm display a red LED and activate a buzzer. If I was able to use a micro controller for this it would be very easy, however I assume I will have to use 3 comparators, which I am not too sure how to go about using, as I've not really used them.

Any help on getting to grips with this analogue project would be deeply appreciated.

Thanks.
 
If you want to use a micro controller then you can just select one with an ADC (analogue to digital converter).

But yes you can also do this with comparators. Have you tried looking up comparator in google, you'll find all the information you need.
 
Sorry I did not state this in my previous question, but the specification states "no micro controllers can be used. yeah I've used google to research the comparators, however I don't underdtand how to use 3 within one circuit?

Thanks.
 
Do you want only one LED lit at any time, or are you happy that all LEDs be lit for an object at <9cm?
If its the latter then you only need three independent comparator circuits.
For the former you would need three window comparators.
 
Ideally I would like one LED lit at one time. How hard would this be in comparison to all three lit at once?
 
Ideally I would like one LED lit at one time. How hard would this be in comparison to all three lit at once?

To have a circuit where all three could be lit at the same time is the easiest circuit. Just three comparator circuits. Try building / or drawing a comparator circuit for just one LED at the moment. Post your progress here and we'll give you more specific help.
 
You could also use an LM3914 dot/bar generator. It has 10 built-in comparators connected to a reference voltage network with drivers to light 10 LEDs sequentially (dot mode) or all in sequence (bar mode) as the input voltage increases. You can, of course, use only 3 of the 10 outputs if that's all you need. But you could use 3 green, 3 orange, and 3 red LEDs, for example, that could light in sequence to the proximity sensor output signal. The 10th output could light another LED and activate the buzzer.
 
That's actually a better Idea!! Something like this:
... Thank you "Crutschow & Misterbenn" I'll try and get on with this now!!
 
Ra,Rb,Rc as a group and Rd,Re,Rf as another
one should be between the reference 3.3V and ground, the other should be from the sensor's output.
Also if you use an op-amp for comparator, it may be ok however the buzzer will not sound, but if you will use a comparator like LM339, the LED's should be between +V and comparator out pin with a series resistor to limit the current.
The sensor sends IR and reads its reflection from surface. The data sheet says it used triangle calculation to avoid reflection differences between shiny and dull objects.
 
A good start on the schematic. As a concept that works but for a working circuit A few modifications are needed.

You've got an op-amp giving you a gain of 1.2 but you've omitted the nesasery resistors to set the gain. You'll be wanting a non-inverting amp, you probably knew this already but omitted it for the sake of simplicity?

You've tied both voltage dividers to the amp signal, this won't work.You'll want the comparitor inverting input to be your voltage reference and the non-inverting to be your signal reference.
So you want the Rd-Rf resistor chain to come off 5v and you don't need Ra-Rc just a direct link from your amp output to comparitor non-inverting input.

I suggest using a Fet at the comparitor outputs, this might not be nesasery depending on the comparitor and LEDs used.

LEDs need series resistor. I think you probably know this.

All ICs should have a capacitor across the power pins and as close as possible.
 
how bout this ,maxim max924 comparator data sheet, page 13 but any similar comparator would work.
 
Your really should consider the LM3914. It has all the resistors and comparators in the chip and also has a current output for the LEDs so you don't need added resistors for that either.
 
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