Load sensor amplifier

i bought two of these 20kg load sensors with 4 wires. but the amount of resistance is so tiny to read. is there an amplifier i can buy to read it or is there a simple circuit i can make myself? please help

Have you tried in another tab with 'google' to search for load cell amplifier, when I did I got back 'About 2,230,000 results (0.31 seconds)', with a zillion images of circuits and products, even some that looked Arduino'ish.

So, yes to both your questions, you can build and obviously you can also buy otherwise such a product would be useless. For building, what are your electronic building skills like?

These load cells are 4 wire and essentially a resistance bridge where you need to provide excitation across the bridge to measure the voltage on the opposite side of the bridge. You don't want to measuring the resistance directly, that won't work.

TrailerTrash:
i bought two of these 20kg load sensors with 4 wires. but the amount of resistance is so tiny to read. is there an amplifier i can buy to read it or is there a simple circuit i can make myself? please help

Typical you supply a well regulated DC voltage to the red + and black - wires (called the excitation voltage), and measure the load cells output voltage across the green and white wires. The output change is so many millivolts per volt of excitation voltage used, so a given load cell will output twice the output voltage for a given load weight if driven by 10 vdc Vc 5 vdc. This small millivolt output is best read via a differential instrumentation op-amp IC where you set the gain of the amp to have the full scale output for the cell match the full scale capacity of your ADC measurement range.

These devices tend to cost around $100 or more for the more robust version such as you shown. There are models available that have a maximum weight range of just some grams and are very sensitive. Load cells’s internal resistance bridge is usually designed to be self-cancelling for temperature changes and are considered industrial quality sensors.

Lefty

so i will do a search for "voltage op-amp IC" gotcha dude, thanx

TrailerTrash: so i will do a search for "voltage op-amp IC" gotcha dude, thanx

Better to search on instrumentation op-amp. Note that standard op-amps can be wired up as a instrumentation op-amp, but such purpose amps tend to have better specifications that support low level measurements.

http://www.google.com/search?q=instrumentation+op+amp+ic&hl=en&tbm=isch&tbo=u&source=univ&sa=X&ei=Qjk1UayLLsatqwHg7IDABg&ved=0CHkQsAQ&biw=1038&bih=788

Lefty

You would be better off if you did search for the terms 'load cell amplifier' as I mentioned. Searching for 'voltage op-amp IC' will not directly lead you to what you need. You will get lots of hits on IC's and not so many for the circuit you need.

As Lefty says, using a load cell needs a special type of op-amp circuit. Many years ago I used really big load cells to measure the weight of CO2 vessels at a beer brewery. The CO2 was a by product of fermentation.

Sorry Lefty, I guess we posted together almost.

thats great but i only shop on ebay and i see several kinds. is this it? http://www.ebay.com/itm/2-pcs-NE5532-Dual-Low-Noise-Op-Amp-Texas-Instruments-/180860200848? no, i need to search for "instrumentation op-amp -texas"

aha i found it, and theres two. http://www.ebay.com/itm/OP06-HIGH-GAIN-INSTRUMENTATION-OP-AMP-NOS-LOT-OF-2-/281060129205

and next i buy this for my SeeLevel II tank sensor strip http://www.ebay.com/itm/270941562338

If I were you, I would buy a ready made load cell amplifier board. From the google search I gave you, here is one such board, nice and small and easily fits in your iCamper, http://www.leobodnar.com/products/LC-amp/ Hook it up and you're done.

You need to know your load cell output volts per volt of excitation.

rockwallaby: If I were you, I would buy a ready made load cell amplifier board. From the google search I gave you, here is one such board, nice and small and easily fits in your iCamper, http://www.leobodnar.com/products/LC-amp/ Hook it up and you're done.

You need to know your load cell output volts per volt of excitation.

Hit buy it and it says not found. Does someone else make/sell such a module? http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=73&products_id=199 Lefty

Bugger. Hit on their contact button or click here and ask them http://www.leobodnar.com/shop/index.php?main_page=contact_us

I'm sure another five minutes spent looking in google search will have you a hand full of similar units.

rockwallaby: Bugger. Hit on their contact button or click here and ask them http://www.leobodnar.com/shop/index.php?main_page=contact_us

I'm sure another five minutes spent looking in google search will have you a hand full of similar units.

Nope, I'm a limited face time impulsive type buyer, they lost this fish that will now swim after some other shiny object. :D

Lefty

so we all came up empty searching so we will design our own onto breadboard. but i see different schematics on google images.

i think i found it at http://cbtechnical.blogspot.com/2011/04/amplifier-circuit.html

one 200 ohm two 10k ohm 0.1 uF capacitor INA-122 (DIP package) chip

I'd'a thunk that the vendor of the loadcell hardware would have sold a compatible, tried-and-tested, electronics package with it?

I would buy this IC http://www.ebay.com/itm/INA125-Instrumentation-Amplifier-w-precision-voltage-reference-INA125PA-OpAmp-/181049159026?pt=LH_DefaultDomain_0&hash=item2a275eed72 I have used INA125's for load cell amps in the past and this has the benefit of a precision voltage that you can excite the load cell with.

For schematics get the datasheet for the IC and read it.

JimboZA: I'd'a thunk that the vendor of the loadcell hardware would have sold a compatible, tried-and-tested, electronics package with it?

They often do, but marketing to the industrial base they tend to be pretty expensive. Omega Engineering company sells lots of load cells and accessories for them.

Lefty

$0.99 50 x Resistors 250 Ohms OHM 1/4W 5% Carbon Film $0.99 50 x Resistor 10K Ohm 1/4W 0.25W 5% Carbon Film $0.99 3 x 0.1uF 50V Radial Capacitor Tantalum $14.28 2 x INA122 Precision Instrumentation Amp, 2-36Vsup R-RO

Total: $17.25

worth it?

TrailerTrash: $0.99 50 x Resistors 200 Ohms OHM 1/4W 5% Carbon Film $0.99 50 x Resistor 10K Ohm 1/4W 0.25W 5% Carbon Film $0.99 3 x 0.1uF 50V Radial Capacitor Tantalum $14.28 2 x INA122 Precision Instrumentation Amp, 2-36Vsup R-RO

Total: $17.25

worth it?

Priceless! ;)

What you'll find is that when the cell is at rest it will report some non-zero voltage (load cells are never perfectly balanced), and then you'll want to get the largest voltage swing possible from that point when load is applied. You'll be doing a lot of fiddling with the gain resistor when you're setting this up and will want to have 500R or 100R or maybe even 10R trimmers on hand to do that.