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### Topic: Arduino Uno r3 + 1kN load cell = how to amplify problem (Read 3791 times)previous topic - next topic

#### TomKraft

##### Jan 31, 2013, 12:18 am
Hi there,

I have the following load cell : http://www.loadcellshop.co.uk/S-Beam-Load-Cells/19-S-Beam-Load-Cell-500N-1kN-2.5kN-5kN.html

in addition I purchased such amplifier http://www.elane.net/index.php?go=loadcell_amplifier

However it will only provide 5v excitation voltage, the load cell requires 10V.

Can I provide the excitation voltage from external supply? This would mean connecting  E+ to +10V, E- to common ground. S+ and S- would go to the amplifier and then +9V to AMP pin V , common ground (proto board) to G and arduino to sense signal via pin S.

I can alternatively build an amp with INA125P but the question remains, can I provide excitaiton voltage to the cell directly, leaving INA V-out disconnected?

Thanks for help!

#### MarkT

#1
##### Jan 31, 2013, 01:05 am
10V is the nominal excitation voltage.  Its still a strain guage at 5V or even 1V, you just get less resolution / more noise.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### retrolefty

#2
##### Jan 31, 2013, 01:31 am
Yes, just drive the bridge with +5vdc. The adjustable gain on that amplifier module will still allow you to set up the output voltage change you required. Looks like nice stuff.

Lefty

#### TomKraft

#3
##### Jan 31, 2013, 01:55 amLast Edit: Jan 31, 2013, 01:58 am by TomKraft Reason: 1
Thanks for help guys. As MarkT mentioned, with only 5V going in I will have 50% less voltage going out of the load cell. Lefty,  Did I understand you correct, that gain on the AMP will take care of that? How about resolution and noise? The cell is 1000N capacity, meaning that for 1N I will have 0.01mV (at 5V) going to AMP and I would like to get 0.1N resolution if possible.

Having that in mind, should I just use the amp as it is (let it provide 5V excitation) or boost the excitation to 10V externally?

#### retrolefty

#4
##### Jan 31, 2013, 02:04 am

Thanks for help guys. As MarkT mentioned, with only 5V going in I will have 50% less voltage going out of the load cell. Lefty,  Did I understand you correct, that gain on the AMP will take care of thatm how about resolution and noise? The cell is 1000N capacity, meaning that for 1N I will have 1mV (at 5V) going to AMP and I would like to get 0.1N resolution if possible.

Having that in mind, should I just use the amp as it is (let it provide 5V excitation) or boost the excitation to 10V externally?

I don't see a resolution issue as the amplifier you are using is analog and the adjustable gain will set the total voltage output measurement range the same no matter if you were using 10v or 5v bridge drive. The downstream analog to digital converter (assuming there will be one) is where resolution of step size is determined depending on if it's a 8,10,12,14, etc bit ADC converter, so it should be the same if handling the same analog input voltage range.

As far as signal to noise ratio goes, certainly the reduced bridge output voltage obtained (1/2) from driving the bridge at 5v Vs 10v, will be less, I don't think you will notice a difference at all in your real world measurements.

Lefty

#### TomKraft

#5
##### Jan 31, 2013, 02:30 am
I planned to use bare Arduino board to read the voltage, so would use on board adc. I possibly could obtain some code and hardware for 24 bit adc bu this would come if thenobtained results were poor.

Thanks Lefty! (Cannondale bikes fanatic?)

#### retrolefty

#6
##### Jan 31, 2013, 02:37 am

I planned to use bare Arduino board to read the voltage, so would use on board adc. I possibly could obtain some code and hardware for 24 bit adc bu this would come if thenobtained results were poor.

Thanks Lefty! (Cannondale bikes fanatic?)

Well 24 bit adc can be a real bear to deal with as far as layout and noise, one rarely can get the full 24 bit range unless buying a completed commercial module. If you find the 10 bit ADC on the arduino not to your final satisfaction (certainly give it a try to start with), Adafruit folks have some really nice I2C 12 and 16 bit ADC modules based on the TI ADS1015/1115 chips. They are really easy to work with, they have a arduino support library available, and really work well, and are a great buy.

http://www.adafruit.com/products/1083
http://www.adafruit.com/products/1085

Lefty

#### TomKraft

#7
##### Jan 31, 2013, 11:57 pm
Will arduino ADC be accurate? It compares the input to ref voltage from USB, which may vary from time to time.

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