need to amp a voltage on a 5 volt dc circuit by 30-80%

W

wol6

New Member

• Sep 23, 2005

• #1

hi all
new it all this so please help

i'm after a amplifer to amp a voltage

i have a circiut working on 5 volts ,
i have a output from 0-5volts
i need a circiut that will change the reads to the reads below
the input reading are the readings i have coming out of my sensor
the output is the voltage i need

input output
0.5v 0.9v
1.0v 1.8v
2.0v 2.6v
3.0v 3.4v
4.0v 4.3v
working on dc voltage
all appox voltages give or take .25v
and to fit a varible resistor to change output from say 30% - 80% increase
from input appox
many thanks wol

or contact me @
scott.welsby@btopenworld.com

 

Styx

Active Member

• Sep 23, 2005

• #2

if you can live with:

Code:

INPUT OUTPUT
0.5	1.365
1	1.78
2	2.61
3	3.44
4	4.27

then it is possible
Those results fit a

y = mx + c

ie

output = 0.83x + 0.95
and y = 0.8x + 1 is pretty close as well

so you will need a gain and a summer

 

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W

wol6

New Member

• Sep 23, 2005

• #3

hi
do you have to have any more connection to the chips?? like earths and lives??
and also how do you get a -1v ref on a 5v dc circuit??
many thanks
wol

 

R

Russlk

New Member

• Sep 25, 2005

• #4

I plotted the response that you want, it is two straight lines, so a simple shaping network will do the job. I will work one up soon and post it.

 

R

Russlk

New Member

• Sep 25, 2005

• #5

This is the circuit, you can use almost any op amp, I used the LT1006 because LM358 is not in the library.

 

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W

wol6

New Member

• Sep 26, 2005

• #6

many thanks

hi
this looks great but can you explain a bit more
i.e
v1 =
v2 =
vr2
and the wiring up of the lt1006
and as for the table
the voltage across the bottom = in
and the voltage up the side = output

the r1,2,3,4 are ok
the d1,d2 are ok
many thanks
scott

 

R

Russlk

New Member

• Sep 26, 2005

• #7

V1 is the input voltage that is swept from 0V to 4V. V2 is the supply voltage, in this case, 12 volts. Vr is just a test point.

I re-drew the schematic to be easier to understand. VCC can be 6V to 12V, altho you will have to tweak R3 at other than 12 volts. The LM358 is a dual op amp, only one is used.

 

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W

wol6

New Member

• Sep 27, 2005

• #8

voltage increase

hi
the pic is great
if i was to run a car wiring the charging voltage in normally 14volts
would this all still be ok
and to change the gain from say 50%-80%
could i fit a variable resistor to increase the output?
many thanks
scott

 

W

wol6

New Member

• Sep 27, 2005

• #9

voltage increase

hi
would it be more stable if i could connect it to the 5v supply as this is more sable voltage
as for the 12volt feed comes to 14.2 when the alternator is charging
many thanks
scott

 

R

Russlk

New Member

• Sep 27, 2005

• #10

The op amp will run out of head room if run at 5 volts and will not reach 4.3 volts output. The error running from 14.2 volts will be minimal but you will want some noise filtering. Keep in mind that voltage spikes on the 12 volts can reach 60 volts. A 6.8 volt zener and 1K resistor would be good insurance. In that case, use 150K for R3.

 

W

wol6

New Member

• Sep 27, 2005

• #11

voltage increase

hi
so if i put A 6.8 volt zener and 1K resistor on to the vcc's (contact both together) zener 1st then the 1k resistor
this would down size the voltage to 6.8volts ?
then put a 150k resistor on the r3 this would compensate for the zener and 1k resistor ?
where would i fit the variable resistor to change the % of gain??
many thanks
wol
p.s a new picture would be great
p.ss have you any dvd players you would like to make region free for your time, as i sell unlock code but you can have for free!!!!

 

R

Russlk

New Member

• Sep 27, 2005

• #12

The 20K pot will allow the gain to be reduced to 1/2 or increased to infinity (not really, but more than you would want). If you want to reduce the gain more, use a larger pot.

 

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4electros

New Member

• Nov 1, 2005

• #13

clarify

could anyone here get to have clue.... just the basic or the pricinple of this post subject .. of course of that 's possible ..

thanks in advance!