Didactic electronic scale (IoT SCALE) (ART555E)

This assembly is the first stage in an even larger project for an electronic IoT scale. In this article, we will deal with a simple assembly where we analyze the analog part, which is simple, without going into the data processing part and sending the information to a central or another device. This assembly can be applied to learn how an electronic scale works and, from there, add improvements to the system until it becomes a scale for commercial or scientific use.

 

Important: this project, as an scale and as it is presented, is not metrologically valid. In other words, this project, as presented, cannot be used commercially as a scale, nor can it be subjected to metrological evaluation. If the necessary implementations and adjustments are made in software and hardware (electronics and mechanics), it is possible to build a real IoT balance based on the concepts presented here.

 

The objective of this project is to set up a scale as easy and intuitive as possible, to highlight its functionalities linked to IoT.

 

Operation

As we can see in Figure 1, we have the circuit and the assembly diagram.

When we put a weight on or put pressure on the RM1 resistive force sensor, the resistance between the terminals reaches a few kohm. When we have no weight or pressure on the RM1 resistive force sensor, the resistance between the terminals reaches Mohms (Megaohms).

 

Protoboard
Protoboard | Haga click en la imagen para ampliar |

 

 

 Diagram
Diagram

 

 

https://drive.google.com/open?id=1I91yUlaT8Kmm79TydQyY5nXUUXm2hFUw

 

The resistor R2 makes it possible to work with the sensor in order to read its values under no-load, under-loading and under-discharge conditions.

We use the multimeter to analyze the operation of the circuit, in other words, the electrical voltage present at the measurement point, which during the loading and unloading of the resistive force sensor. The reader can add LEDs to the system instead of the multimeter.

 

Editorial note: we also suggest using our ART329E to obtain a “simplified digital scale” with 4 scale points, expandable to 8. An interesting didactic setup.

 

 

Assembly

The assembly is very simple, it was applied to a 440-pin protoboard. Below, we have a photo of the assembly and a video of its operation. The material used is easy to find and is found in the list below.

 

Link to video of its operation:

https://drive.google.com/open?id=1BnRXOS87-6TKhN0uOTwNIw3zpxrSTSDu

 

1 - 5V / 1A USB source (here, a simple cell phone charger with micro-USB connection fits well)

1 - resistive force sensor 0.5 "

1 - 1k / 0.25W resistor

1 - 440 point protoboard

Male-male and male-female jumpers

 

Conclusion

With this simple circuit, the resistive force sensor was tested, thus verifying its resistance variation inversely proportional to the load / force variation on it. Also, using this circuit topology used in this test, it is possible to verify (in a very similar way) the operation of any analog sensors that present as variable magnitude the resistance between their terminals (like an LDR, for example).

 

 


Circuit Bench