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amplify 3.5 volt to 5 volt

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agmechatronics

New Member
hi every body
i have an analog signal from a sensor it is varying between 2.5 volt to 3.5 volt and i want to amplify it to (zero volt and 5 volt)
what is your suggestions
thank you
 

JLNY

Active Member
There are a lot of factors to consider, but I think the simplest solution would basically boil down to an op amp in a non-inverting configuration with a fixed gain. If you need higher current, you may need to add a buffer in front of it.

Also keep in mind that if you run an op-amp on a regular 5V supply, it will not swing all the way to 5V, but will come pretty close depending on what you use. If this is just an amplifier for an ADC or something like that, this may be acceptable. If you absolutely need the voltage to swing all the way to 0 and 5 volts and not just as far as the op amp will swing for a 5V supply, you may need a positive supply rail higher than 5V.

What is the application?
 
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alec_t

Well-Known Member
Most Helpful Member
Welcome to ETO!
You can use an op-amp configured as a non-inverting one with a gain of 5 and an off-set of -2V. The op-amp will, however, need a supply voltage greater than +5V. It may also need a negative supply voltage if you want exactly 0V at the output.

Edit: JLNY beat me to it!
 

agmechatronics

New Member
There are a lot of factors to consider, but I think the simplest solution would basically boil down to an op amp in a non-inverting configuration with a fixed gain. If you need higher current, you may need to add a buffer in front of it.

Also keep in mind that if you run an op-amp on a regular 5V supply, it will not swing all the way to 5V, but will come pretty close depending on what you use. If this is just an amplifier for an ADC or something like that, this may be acceptable. If you absolutely need the voltage to swing all the way to 0 and 5 volts and not just as far as the op amp will swing for a 5V supply, you may need a positive supply rail higher than 5V.

What is the application?
 

agmechatronics

New Member
ok
the application a laser stop device it consist of a laser source and photo-diode sensor to receive the beam of laser then to a micro controller and when i cut the beam an indication led is turn on the problem is the beam is cut by a very small thin string about 0.1 mm and this give a very small signal its not noticed as i cut the beam with my hand or with an wire about 1 mm
so i need to amplify the signal
 

ericgibbs

Well-Known Member
Most Helpful Member
hi ag,
How quickly does the string cut/block the laser beam.
Is the 2.5 volt to 3.5 volt pulse or a level signal.
E
 

alec_t

Well-Known Member
Most Helpful Member

MikeMl

Well-Known Member
Most Helpful Member
hi every body
i have an analog signal from a sensor it is varying between 2.5 volt to 3.5 volt and i want to amplify it to (zero volt and 5 volt)
what is your suggestions
thank you
Start reading at post#68 in this forum thread. A bit simpler than your post #6.

Gain = (5-0)/(3.5-2.5) = 5
Gain of a non-inverting amplifier = 1+R2/R1, so R2/R1=4

Pick R1 = 10K, therefore R2=40K

Middle of V(in) input range = (2.5+3.5)/2 = 3V
Middle of V(out) output range = (5+0)/2 = 2.5V
(V(ref)-V(in))/R1 = (V(in)-V(out))/R2

Subst, and rearrange, V(ref) = (R1/R2)*(V(in)-V(out)) + V(in) = (10K/40K)*(3-2.5) + 3 = 3.125

34a.png
 
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MikeMl

Well-Known Member
Most Helpful Member
You detect the AC not the DC.
Good idea. You could have an AC gain much higher than the gain of 5 in my post above... If you block DC, then the amplifier adjusts itself (slowly) for ambient light changes.
 

ericgibbs

Well-Known Member
Most Helpful Member
Good idea. You could have an AC gain much higher than the gain of 5 in my post above... If you block DC, then the amplifier adjusts itself (slowly) for ambient light changes.
This is why I asked the OP ref the laser beam 'blocking' speed, an AC coupled amplifier could be a better solution.

Another option would be DC amplifier/slicer with a limited auto ambient light correction.

The OP has not said how the amplified signal is going to be used.?
I am assuming just a pulse detection circuit.?

E
 
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