# How to connect this strain gauge?

#### kusspuss

Aug 25, 2023
32
recently i bought this strain guage where vender said it is 4bridge, i am not sure how to connect this with power suppl so that this strain gauge operate safe the resistance of bridge is 120ohm strain gauge.

#### Attachments

• sG.jpg
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• SG1.jpg
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Feb 19, 2021
621
Its a full bridge strain gauge, so power goes to Red and Black,
Green and White to A/D or IA input.

The lower R valued ones may need a R in series with power connection
to limit current, which creates a CM Voltage so A/D has to be differential
input, or use IA. Does information describe current limit allowed, max ?

Regards, Dana.

#### kusspuss

Aug 25, 2023
32
Its a full bridge strain gauge, so power goes to Red and Black,
Green and White to A/D or IA input.

The lower R valued ones may need a R in series with power connection
to limit current, which creates a CM Voltage so A/D has to be differential
input, or use IA. Does information describe current limit allowed, max ?

Regards, Dana.
yes i have AD620 module too amplify it , the vender told me 25mA.how much safe power supply should give and how can i connect this with breadboard

Edit: do i need voltage divider , i have voltage regular 3-24V DC

thankyou very much

Last edited:

Feb 19, 2021
621
A good starting point would be Fig 38 in :

Regards, Dana.

#### kusspuss

Aug 25, 2023
32
A good starting point would be Fig 38 in :

Regards, Dana.
i understang this Amp , i want to know that how should i suppl power

Feb 19, 2021
621
What A/D are you going to use to read the output of AD620 ?
In other words what is the desired output range you want out

Will you be feeding the AD620 output to an A/D, if so whats is
its input range allowed ?

Regards, Dana.

#### kusspuss

Aug 25, 2023
32
What A/D are you going to use to read the output of AD620 ?
In other words what is the desired output range you want out

Will you be feeding the AD620 output to an A/D, if so whats is
its input range allowed ?

Regards, Dana.
the mv voltage from AD620will be feed into Arduino , the voltage allowed output from AD620 is 9V .

Feb 19, 2021
621
Tha allowed Arduino input range is 0 - Vcc, Vcc is either 3.3 or 5V.

So you cannot overdrive the input. Circuits you can use to accomplish this :

The Ad620 has to be operated at higher V than Arduino Vcc if you want maximum range, becuse its limited,
not rail to rail :

Regards, Dana.

#### kusspuss

Aug 25, 2023
32
Tha allowed Arduino input range is 0 - Vcc, Vcc is either 3.3 or 5V.

So you cannot overdrive the input. Circuits you can use to accomplish this :

The Ad620 has to be operated at higher V than Arduino Vcc if you want maximum range, becuse its limited,
not rail to rail :

View attachment 60410

Regards, Dana.
if i supply 3-5 V to AD620 , will it will be enough ? secondly i want to know that how can i suppl power to 4 strain gauge full bridge if wheatstone bridge not required

#### bertus

Moderator
Nov 8, 2019
3,034
Hello,

The AD620 works from +/- 2.3 AKA 4.6 Volts;

This is the gauge circuit from the datasheet:

Bertus

#### Attachments

564.4 KB · Views: 0

Aug 25, 2023
32

#### Attachments

• n.jpg
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#### bertus

Moderator
Nov 8, 2019
3,034
Hello,

It looks like it uses a ICL7660 as voltage converter for the negative voltage:

Bertus

#### kusspuss

Aug 25, 2023
32
Hello,

It looks like it uses a ICL7660 as voltage converter for the negative voltage:
View attachment 60415

Bertus
so i should supply 3.5-10V to AD620?

Feb 19, 2021
621
The gauge circuit is driving the ground, in this case, of the Arduino which would
pose additional problems interfacing to it.

You have a bridge, connected to Vcc, lets say 5V. Its CM V is 2.5V. Its deviation
you have to compute, but for this example, when bridge unbalanced ranges
+/- 100 mV. So its output ranges from 2.6V to 2.4V.

Your arduino, says its running off 5V, the A/D input range is 0 - 5V.

So you have to translate 2.4V to 2.6 V to 0 V to 5.0 V. So start with G needed.
G = 5V / .2V = 25. So that gives you the slope of Vout / Vin.

Now you have to offset that by the CM voltage of 2.5 V so you get 0 - 5 V.
The easy way is to have a - supply as well on AD620 and use a OpAmp
differential circuit to subtract out the offset. A tool you can play with :

A design method for offset OpAmp is :

Of course you dont have to use the entire range of Arduino A/D, you can
trade that off for other considerations.

For negative supply you can use PWM output of Arduino and this :

Because the AD620 has excellent PSRR that should be OK, but doing an error buget or
sim always prudent.

Regards, Dana.

Last edited:

#### bertus

Moderator
Nov 8, 2019
3,034
Hello,

The 10 Volts limit is set by the ICL7660.
It could be lower as 3.5 Volts, The LM358 works from +/- 1.5 Volts, The AD620 from +/- 2.3 Volts.
The board should be able to handle 2.3 to 10 Volts.

Bertus

#### Attachments

• LM158 LM258 LM358.pdf
1,009.4 KB · Views: 1
• icl7660.pdf
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Feb 19, 2021
621

Sim for -V generator, you will have to juggle values to get AD620 output
swing down to 0V (to maximize Arduino A/D input range). Also use Schottky
diodes versus the Si I used, to get more - V. Basically strive for
~ 2V so that AD620 can swing to ground. Note using Schottky's versus IN914
should get closer to -2V needed.

I ran Arduino PWM at 1 Khz.....to drive this neg V generator.

Regards, Dana.

Last edited:

#### kusspuss

Aug 25, 2023
32
Hello,

The 10 Volts limit is set by the ICL7660.
It could be lower as 3.5 Volts, The LM358 works from +/- 1.5 Volts, The AD620 from +/- 2.3 Volts.
The board should be able to handle 2.3 to 10 Volts.

Bertus
for this Fully strain gauge bridge how can i power it up , there are four terminals , two terminal S+ and S- go to AD620 signal + and signal -

#### kusspuss

Aug 25, 2023
32
The gauge circuit is driving the ground, in this case, of the Arduino which would
pose additional problems interfacing to it.

You have a bridge, connected to Vcc, lets say 5V. Its CM V is 2.5V. Its deviation
you have to compute, but for this example, when bridge unbalanced ranges
+/- 100 mV. So its output ranges from 2.6V to 2.4V.

Your arduino, says its running off 5V, the A/D input range is 0 - 5V.

So you have to translate 2.4V to 2.6 V to 0 V to 5.0 V. So start with G needed.
G = 5V / .2V = 25. So that gives you the slope of Vout / Vin.

Now you have to offset that by the CM voltage of 2.5 V so you get 0 - 5 V.
The easy way is to have a - supply as well on AD620 and use a OpAmp
differential circuit to subtract out the offset. A tool you can play with :

A design method for offset OpAmp is :

Of course you dont have to use the entire range of Arduino A/D, you can
trade that off for other considerations.

For negative supply you can use PWM output of Arduino and this :

View attachment 60416

Because the AD620 has excellent PSRR that should be OK, but doing an error buget or
sim always prudent.

Regards, Dana.
i have question that the Module i have , do i need to make another OP and connect AD620 MOdule with it ?

#### bertus

Moderator
Nov 8, 2019
3,034
Hello,

I have written the boards input names on your sensor picture:

Do you have a datasheet of the gauge?
That way we can see the maximum exiting voltage of the gauge.

Bertus

#### kusspuss

Aug 25, 2023
32
Hello,

I have written the boards input names on your sensor picture:
View attachment 60422

Do you have a datasheet of the gauge?
That way we can see the maximum exiting voltage of the gauge.

Bertus
the company said that , the working current during static measurement is about 25mA , unfortunately could not find datasheet

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