Measuring Weight with Strain Gauges and Load Cells

The world of precision measurement is vast and fascinating, and one of its many applications is measuring weight using strain gauges and load cells. These devices have become an essential tool for engineers, scientists, and makers alike, offering a high degree of accuracy and versatility in measuring forces.

One common method used to measure weight is by utilizing strain gauges. Strain gauges are small resistive sensors that change their resistance when subjected to mechanical stress, such as pressure or force. The basic setup involves gluing the strain gauge to an object we want to apply force to and measuring its resistance right after it's been applied. However, this approach has a major drawback: non-extreme weights create a very small, almost negligible change in resistance, making it difficult to measure accurately.

To overcome this issue, a Wheatstone bridge is employed. By replacing the single strain gauge with multiple resistors – typically precise 120 ohm resistors – and applying a faithful supply voltage to the circuit, we can get a voltage difference of zero volts between the resistors when no forces are applied. This setup effectively converts the change in resistance into a measurable voltage, which can be amplified by a differential op-amp configuration. With a gain of 196 for example, this allows us to accurately measure the force applied.

However, there's another challenge that arises from the nature of strain gauges: temperature sensitivity. The resistance of these sensors is highly dependent on temperature, and small changes in temperature can lead to significant errors in measurement. This is why it's recommended to use a Wheatstone bridge with two or four strain gauges to mitigate this issue. By having both strain gauge resistances influenced by the temperature, any temperature-related errors are effectively abstracted away.

While building up a proper strain gauge setup can be time-consuming and daunting, there's an alternative solution known as load cells. These devices consist of aluminum profiles with multiple holes for mounting and come pre-equipped with a Wheatstone bridge already attached. All that needs to be done is connect the red wire to 5 volts deep and the black wire to ground, then measure the voltage between the white and green wires. This setup correlates directly with the force applied to the load cell.

To create an accurate scale using this method, we need to build up a simple amplifier circuit as before. However, there's an even simpler solution: removing the op-amp circuits and utilizing the HX7-111 breakout board from Sparkfun. The HX7-111 features a 24-bit ADC with an integrated amplifier that boasts a maximum gain of 128. By soldering this chip to its right connector, we can amplify the voltage signal received from the load cell. Connecting the data pin to Pin 7, the clock pin to Pin 8, and powering it through 5 volts and ground, we can use the Arduino library provided by Sparkfun to output the readings through the serial monitor.

This setup offers a significant advantage over traditional strain gauge setups: with a 24-bit resolution that equals voltage steps of 0.298 micro-volts, we can measure much smaller forces than before. While this may lead to more noise in the readings, it allows us to accurately measure forces with greater precision and flexibility.

In conclusion, measuring weight using strain gauges and load cells has become an essential skill for engineers, scientists, and makers. By understanding the basics of these devices and their applications, we can create accurate and reliable measurement systems that are capable of detecting even small changes in force. Whether through traditional strain gauge setups or more modern solutions like load cells and HX7-111 breakout boards, there's a wealth of options available to suit our needs.

In addition to being used for measuring weight, these devices have numerous applications across various fields. For example, in aerospace engineering, strain gauges are often employed to measure stress on aircraft components during flight tests. In industrial settings, load cells are commonly used to weigh materials and track inventory levels. And in robotics and automation, precision measurement is crucial for controlling movement and detecting forces.

The world of precision measurement is vast and fascinating, and it's exciting to see how these devices continue to evolve and improve with new technologies. As makers and engineers, we can harness the power of strain gauges and load cells to create innovative solutions that push the boundaries of what's possible.

WEBVTTKind: captionsLanguage: enfor the past year I've been working in secrets on an improved version of my electric longboard and so far I implemented a new power switch and new remotes a new control circuits that cannot only receive information from the remote wirelessly but also integrates a weight measuring system this way if you ever lose control of the electric longboard and must jump off it recognizes stats and breaks automatically the key component that makes this weight measuring system possible is a so-called strain gauge which is attached to my longboard underneath a protective layer of silicon such strain gauges are actually pretty common when it comes to measuring masses or forces electrically so in this video let's have a closer look at them and find out how we can integrate them in the circuits in order to measure weight / force easily over my controller let's get started on closer inspection is a strain gauge just a flexible piece of plastic on which a zig-zag pattern of resistance wire is secured by soldering two thin wires to its contacts and measuring the resistance of this particular strain gauge then we get a value of around 120 point 4 ohms which correlates with its data sheets besides the 120 ohm value there also exists 358 700 or 1000 ohms as standard values and while my example strain gauge is kind of big there also exists smaller variations even sometimes with different patterns but enough about the outer appearance let's rather find out how a piece of plastic can measure weights and the answer is actually quite simple by stretching or compressing the strain gauge the resistance of which wire pattern increases or decreases slightly that means the strain of the strain gauge is proportional to its resistance which logically means we can calculate the mass of an object so all we have to do is to properly glue the strain gauge to the object we want to apply force to and measure its resistance rights well it's not that simple since non extreme weights aka more realistic forces only create a very small almost not measurable change in the resistance what we have to utilize instead to fix this problem is a so-called wheatstonebridge by replacing our one with the strain gauge and the rest of the resistors were precise 120 ohm resistors and applying a faithful supply voltage to the circuits we would get a voltage difference of zero volts between the resistors if no forces applied and the voltage proportional to the strain the forces applied that means we successfully converted the change in resistance into a voltage that we could now amplify with a differential op amp configuration we have a gain of for example 196 and then measure it with the analog to digital converter of a microcontroller but there's still a noticeable problem which comes to mind when we have a look at the data sheets it seems like the resistance of our strain gauge is temperature sensitive which can easily mess up the measured voltage difference of the wheatstonebridge that is why you usually avoid such a quarter bridge with only one strain gauge and instead utilize a half bridge with two strain gauges or a full bridge or four strain gauges I always like to use the half bridge since both strain gauge resistances are influenced by the temperature and this mistake then gets abstracted by the nature of the Wheatstone bridge of course you could also use four strain gauges to compensate for all kinds of undesired forces but let's rather stick to the basics for now now to easily adjust the resistance values of three and AH four corresponding to the strain gauge values it is recommended to utilize ten turn trimmers so that after building up the circuits and connecting the strain gauges you can adjust them until the output of your microcontroller ADC splits out the voltage in between the supply voltage and ground now by applying force to the objects we can see that the a DC's measured values change accordingly which means we can use those values to measure weights but since building up a proper strain gauge setup can be quite daunting and time-consuming there's also a cheap and easy alternative known as a load cell those are basically aluminum profiles were four and four holes for mounting to which a complete wheatstonebridge is already attached all we have to do is to connect the red wire to five volts deep black wire to ground and measure the voltage between the white and green wire like before it is the voltage difference of the wheatstonebridge that once again correlates with the force that we apply it to the load cell that means we could simply attach the load cell to two pieces of woods with m4 spacers and screws build up the same amplifier circuit as before feed it into Nod we know and use the setup as a crude scale but another even simpler solution is to remove the op-amp circuits and instead utilize this HX seven one one breakout board the HX seven one one I see here is a 24-bit ADC with an integrated amplifier that features a maximum gain of 128 by soldering for virus to its right connector pets and thus connecting its data pin to pin 7 its clock pin to pin 8 and its power pins to 5 volts and ground oven Arduino and connecting it's a plus e minus a minus and a plus pets to the load cell wires like I showed right here and utilizing VHX seven-11 Arduino library from Sparkfun we can output this readings through the serial monitor which now reacts even to the tiniest changes in weights the reason is that the 10-bit ADC of the atmega328p male controller features a resolution of 1024 steps which equals voltage steps of 4.9 millivolts but now we got a 24-bit resolution which equals a total of lebanon arts 16,777,216 steps which subsequently equals voltage steps of 0.298 micro volts this way we might get more noise in the readings but we can measure way smaller forces and with that being said you should now be familiar with the basics of strain gauge / load cells and how to use them to measure weight easily I hope you enjoyed watching this video if so don't forget to Like share and subscribe stay creative and we'll see you next timefor the past year I've been working in secrets on an improved version of my electric longboard and so far I implemented a new power switch and new remotes a new control circuits that cannot only receive information from the remote wirelessly but also integrates a weight measuring system this way if you ever lose control of the electric longboard and must jump off it recognizes stats and breaks automatically the key component that makes this weight measuring system possible is a so-called strain gauge which is attached to my longboard underneath a protective layer of silicon such strain gauges are actually pretty common when it comes to measuring masses or forces electrically so in this video let's have a closer look at them and find out how we can integrate them in the circuits in order to measure weight / force easily over my controller let's get started on closer inspection is a strain gauge just a flexible piece of plastic on which a zig-zag pattern of resistance wire is secured by soldering two thin wires to its contacts and measuring the resistance of this particular strain gauge then we get a value of around 120 point 4 ohms which correlates with its data sheets besides the 120 ohm value there also exists 358 700 or 1000 ohms as standard values and while my example strain gauge is kind of big there also exists smaller variations even sometimes with different patterns but enough about the outer appearance let's rather find out how a piece of plastic can measure weights and the answer is actually quite simple by stretching or compressing the strain gauge the resistance of which wire pattern increases or decreases slightly that means the strain of the strain gauge is proportional to its resistance which logically means we can calculate the mass of an object so all we have to do is to properly glue the strain gauge to the object we want to apply force to and measure its resistance rights well it's not that simple since non extreme weights aka more realistic forces only create a very small almost not measurable change in the resistance what we have to utilize instead to fix this problem is a so-called wheatstonebridge by replacing our one with the strain gauge and the rest of the resistors were precise 120 ohm resistors and applying a faithful supply voltage to the circuits we would get a voltage difference of zero volts between the resistors if no forces applied and the voltage proportional to the strain the forces applied that means we successfully converted the change in resistance into a voltage that we could now amplify with a differential op amp configuration we have a gain of for example 196 and then measure it with the analog to digital converter of a microcontroller but there's still a noticeable problem which comes to mind when we have a look at the data sheets it seems like the resistance of our strain gauge is temperature sensitive which can easily mess up the measured voltage difference of the wheatstonebridge that is why you usually avoid such a quarter bridge with only one strain gauge and instead utilize a half bridge with two strain gauges or a full bridge or four strain gauges I always like to use the half bridge since both strain gauge resistances are influenced by the temperature and this mistake then gets abstracted by the nature of the Wheatstone bridge of course you could also use four strain gauges to compensate for all kinds of undesired forces but let's rather stick to the basics for now now to easily adjust the resistance values of three and AH four corresponding to the strain gauge values it is recommended to utilize ten turn trimmers so that after building up the circuits and connecting the strain gauges you can adjust them until the output of your microcontroller ADC splits out the voltage in between the supply voltage and ground now by applying force to the objects we can see that the a DC's measured values change accordingly which means we can use those values to measure weights but since building up a proper strain gauge setup can be quite daunting and time-consuming there's also a cheap and easy alternative known as a load cell those are basically aluminum profiles were four and four holes for mounting to which a complete wheatstonebridge is already attached all we have to do is to connect the red wire to five volts deep black wire to ground and measure the voltage between the white and green wire like before it is the voltage difference of the wheatstonebridge that once again correlates with the force that we apply it to the load cell that means we could simply attach the load cell to two pieces of woods with m4 spacers and screws build up the same amplifier circuit as before feed it into Nod we know and use the setup as a crude scale but another even simpler solution is to remove the op-amp circuits and instead utilize this HX seven one one breakout board the HX seven one one I see here is a 24-bit ADC with an integrated amplifier that features a maximum gain of 128 by soldering for virus to its right connector pets and thus connecting its data pin to pin 7 its clock pin to pin 8 and its power pins to 5 volts and ground oven Arduino and connecting it's a plus e minus a minus and a plus pets to the load cell wires like I showed right here and utilizing VHX seven-11 Arduino library from Sparkfun we can output this readings through the serial monitor which now reacts even to the tiniest changes in weights the reason is that the 10-bit ADC of the atmega328p male controller features a resolution of 1024 steps which equals voltage steps of 4.9 millivolts but now we got a 24-bit resolution which equals a total of lebanon arts 16,777,216 steps which subsequently equals voltage steps of 0.298 micro volts this way we might get more noise in the readings but we can measure way smaller forces and with that being said you should now be familiar with the basics of strain gauge / load cells and how to use them to measure weight easily I hope you enjoyed watching this video if so don't forget to Like share and subscribe stay creative and we'll see you next time