TRT-25 and Arduino Uno

I am reaching out for help on a project I am working on. We are trying to integrate a reaction torque sensor and I am having a hard time deciding how to go about it. Previously I assumed that like my load cell I would be able to use the HX711 module to connect my Torque sensor to my Arduino. The Torque sensors uses a Wheatstone bridge configuration, which is great for this module. The problem I ran into is that the TRT-25 Torque sensor requires an excitation voltage of 10V and my Arduino is only supplying 5V. When I tried powering my sensor separately with 10V I quickly found out that these HX711 modules are not designed to handle 5V...

Needless to say that I am now wondering how I should be power my sensor, but also which A/D converter can be used to get this working. The same manufacturer sells all the components to get this working, but it is hundreds of dollars more and our budget doesnt allow for it. I am posting links here so you can see the sensor. What I am considering now is finding a 10V source and connecting the signal pins to my analog pins on my Arduino. I am hoping based on the raw value I can compute a torque measurement based upon this small piece of information their tech support gave me. (X mv/v * EXCITATION v = TORQUE in/lbs).

FYI, I don't have much more information outside of what it is on the site for the sensor. My project uses a small enclosure and I have a Arduino proto shield to power my other 3 sensors. I am limited on space but could probably incorporate a small supply and replace the current HX711 module.

Did you try the E+ and E- pins on the unknown module for excitation? 25 oz in will still be 2mV/V, if excitation voltage is 4V, 25 oz in will be 8mV instead of 20.

You should be able to use the excitation from the HX711, as @JCA34F has mentioned all that will happen is scaled down readings.
@pcr6955 pinouts of sensor;

Tom... :grinning: :+1: :coffee: :australia:

Hi, I am using the HX711 with the HX711_library for a project.

I am using a torque sensor (TRT-25) which has been calibrated for giving torque given a mV/V value.

Is there some way to get the HX711 readings converted in mV/V (from the library API or manually)? The data I am currently getting with the (scale.get_units()) is a really high value I dont understand. Please help.


I will take a SWAG, it has been a very long time for me doing something like this. If I remember torque sensors have a minimum signal of x mV /V , or at least x millivolts for each volt of applied excitation at full scale torque. You can use simple math to convert the values. These values are dependent on the excitation voltage. It is like a bridge with a variable leg in the circuit.

This is the formula I have (mv/v * excitation (5v) = in/lbs). I already began calculating some of these values. So I know what to expect based on the mV being read. I only have 5V to power my sensor, so already my readings are expected to be half what the document says. The part I am confused on is how to incorporate this in my program. Should I still be using these HX711 libraries and the module? Or would recommend not using this HX711 at all and going some other route?

That's quite an expensive sensor, so it is surprising that you'd want to use a hobbyist ADC such as the HX711 for it, but you certainly can. A better alternative would be the compatible components provided by the sensor manufacturer. But if you do use the HX711, use its excitation voltage, which is stable, not your 5v supply.

You should calibrate your system with known torques (if possible) and then interpolate/extrapolate based on the raw HX711 output at the known torque(s).

Alternatively, you could estimate the torque thus: approximate torque = raw count x full scale torque / (sensitivity x gain x 2^24), provided that under no load the raw count is zero.

For example, if you use channel A (128 gain), and for some random torque your raw count is 2,000,000, then the torque should be approximately 2,000,000 x 25 in-lb / (0.00252 x 128 x 2^24) = 9.2 in-lb

The long way to that result is: with an excitation of, say, 4.3 volts, under full load the sensor will input about 0.00252V/V x 4.3V = 0.0108V to the HX711. With a 128 gain, the HX711's ADC will see 128 x 0.0108V = 1.39V. That's this fraction of the ADC's voltage capability: 1.39V / (4.3V/2) = 0.645 So at full torque, the HX711 should output a count of (0.645 x 2^24) / 2 = 5,411,700 And if everything is linear, then a raw count of 2,000,000 represents (25 in-lb / 5,411,700 ) x 2,000,000 = 9.2 in-lb

This should be adjusted, 'course, if under no load the raw count is not zero.

@DaveEvans Thanks for getting back. I am seeing that the raw count is not 0 so I am still a bit stumped on how to determine what my raw count should see. I am getting 6 digital values when using the read() function from HX711 library.

@pcr6955, please do not cross-post. Threads merged.

When you tested your sensor with 10 v excitation, as recently discovered when your other thread was merged into this one, you violated the common mode limit shown in the datasheet. If I were you, I'd be using a new, un-violated HX711.

Also, there are versions of the HX711 that don't have E- connected to ground. You should ensure you don't have one of those.

I assume you mean you are getting a six digit no-load raw count.

If you are doing this ^^^ as recommended, then you don't need to "determine what your raw count should (be)". Just take the raw count at no load and the raw count at full (or some other) load(s), and interpolate between the two (or more) points.

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