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 16777216 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.
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