Hi,
I am not a pro in either electrics or electronics. So, my question might seem a little bit strange. I have read your datasheets and almost all the comments. But, I couldn’t find the exact spot/terminal on your load cell amplifier shield to add resistor to change the gain. Also, please let me know whether the resistor added to the shield needs to be soldered or we can simply plug it in a socket on the board. Please, clarify this issue in a way that I would not have to ask another question in this regard. In addition, please let me know if we add resistor to that spot/terminal on the shield, whether we would be needing to change the Arduino code ( or adding something to the code) or it has a self-correction ability.
@CE The Gain resistor is SMD Resistor already soldered on the Shield. Please see the picture “Amplifier Gain Resistor” in the section “Gain” in this article. The default resistor value is 100ohms for a gain of 495. The formula to calculate the gain resistor knowing the gain you want is Rgain= 49400/(Gain-1). To modify the gain, you will need to desolder the gain resistor and replace it with the resistor you have calculated. Please note that you will need some SMD soldering experience to do this. You won’t need to modify the code.
Thanks.
I want to measure the water pressure of the pipe by attaching a strain gauge outside the pipe and form a wheat stone bridge and then take the Excitation + and Excitation- and Signal + and Signal- and plug them in to your shield while being stacked on my Arduino Uno board and then Using your Arduino code file, read the strain and interpret it to pressure using Hoop pressure equation and Hook’s law. I was wondering whether the above-mentioned approach is the correct way to measure the water pressure inside the pipe or I should take another action to do so? (since your shield is designed to work with load cell and not my customized wheat stone bridge). Your help would be extremely appreciated on this matter.
Regards
@CE Although the Shield is specifically designed to work with Load Cells, it should in theory work with any Wheatstone Bridge (as long as it is in the requirements of the amplifier’s voltage specifications). However, since you are planning to measure water pressure, you might want to use a Pressure Sensor as this Bar30 High-Resolution 300m Depth/Pressure Sensor or this Adafruit Water Flow Sensor
Hi,
Thanks.
I used my wheatstone bridge (instead of loadcell) on the bread board and connected it to your amplifier and then using Arduino Uno and your Arduino code I got the force.So, it seems that it is working. As I said, I am using a quarter-wheatstone bridge to measure water pressure inside the pipe. I simply, attached a single strain gauge on the water tube and using wheatstone bridge concept and also your amplifier, read the forces using Arduino Uno and your Arduino code. the only problem is that your Arduino code gives me forces instead of pressure. Could you let me know by what number (Area) I should divide the force that I get from serial monitor to have pressure.
@CE As you are aware, force is pressure over an area. In the case of most load cells, the area is minimal, and whatever calculations you make will not provide accurate results. Can you create a new topic on the RobotShop forum with diagrams / images of your setup? Perhaps we can suggest options.
Hi, I am trying to use Uno with this shield and an industrial pressure transducer (full bridge) with 5V excitation and 20mV/V sensitivity. Applying 3000psi (3/5 of full scale) and exciting with 3.3V should yield ~40mV, or analogRead result of 8. With the shield, I am getting analogRead of 15, or ~74mV compared to 0psi. Does that mean that the effective gain of the shield is 1.85, and not 495 with the stock 100Ohm resistor? Moreover, I’ve read in one of the threads above that the shield output varies within 1.25V within 0-3.3V range - what are the input limits then if thew gain is 495? Essentially the same question, I suppose. Hope someone can advise. Thank you!
@Ivan The Wheatstone Bridge Shield output should saturate at about 1.8V (when 3.3V powered) due to the 1000Hz low pass-filter in the output. This means that with 40mV output from the wheatstone bridge, the output of the whatstone bridge shield (one of the analog pins) should be 1.8V with a gain of 45 and you should get an AnalogRead of 360. Please post on the RobotShop forum or contact us on our Support Center with pictures of your setup and as much as possible of details.
I am trying to measure strain on a barbell with 3 strain gauges, they are suppose to be set up in a quarter bridge circuit and each strain read individually. the reason for this is to eliminate error due to bar rotation. Can I use this shield for this application?
@Ethan We suggest you to post your question on RobotShop’s forum with more details/drawings on your project to have the RobotShop’s community input about this.
Hi i purchased the board to use for final year project. i’m planning on using the board to read strain measurement from two strain gauges. i started to run the test procedure to see if the board is functioning correctly. i was able to adjust the first pot to give the correct value but the second did not respond to the pot it just kept going up and down on its ow. any help would be appropriated
Hi i’m a mechanical student so i’m not too familiar with electronics. my question is how do i actually calibrate the board to read strain values. ive gone to the test procedure and iv applied my strain gauge but i dont seem to be getting any readings
@Damilola A linear 2 point calibration with 2 known loads is possible. You can find an Arduino example code performing a calibration through this link.
Here is also a link for the Github repository of the Shield.
In case you have gone through the testing procedure and the RAW values you’ve got are not near the minimum and maximum for each test, than please contact us through our Support Center.
Is there a way to amplify the signal? I changed the gain resistor from 100 ohm to 10 ohm as suggested, but my 20kg load cell flat lines at 2 kg now - also the signal isn’t great compared to if I use the amplifiers in digital mode.
These load cells come with amplifiers - is there a way to hook them up to analog input like you’re suggesting?
I’ll mention I’m a ChemE, so I’m not super familiar with anything circuitry related, as was probably evidenced in the question I asked.
@Peter It will depend on the amplifier circuitry attached to the load cell you have. If you load cell comes already interfaced with an amplifier + ADC, the output from the ADC won’t work with the shield. This Load Cell Shield is intended to work directly with wheatstone-bridge based load cells. You can probably remove the attached amplifier+ADC stage from your Load Cell and connect directly the Excitation+/- and Output+/- wires from the load cell on the shield.
