Structure and principle of a cellular or Wi-Fi hive scale

The structure and principle of all cellular and Wi-Fi hive scales are very similar and are described below. The terms "beehive scale," "hive scale," or "bee scale" are used synonymously in this article. This is a weighing device used to determine the weight change of a bee colony.

GPRS is a packet-based service for transmission in GSM networks. GSM is the abbreviation for Global System for Mobile Communication and describes the transmission protocol for mobile communications.
 

I.) Weighing module or load cell module
 

The weighing module essentially consists of two parts: a load cell and a structure that applies the weight to the load cell. The load cell is usually an aluminum block that bends under the force of the weight. A strain gauge is attached to this aluminum block, which changes its resistance proportional to the strain. This resistance is part of a bridge circuit. The change in resistance of the strain gauge is converted into a small voltage change by the bridge circuit.

In order for the weight of a bee colony to act on the load cell, a corresponding construction is necessary. Many hive scales use a steel construction, as shown in Figure 2. This construction has proven itself over many years. To protect against corrosion, the steel is usually galvanized (electrogalvanized or hot-dip galvanized) or painted. Hot-dip galvanized offers the best corrosion protection, although electrogalvanized hive scales may be more visually appealing.

However, new designs have also been developed in recent years. Some new hive scales also use four load cells mounted in all corners. This eliminates the need for the heavy steel construction. This makes sense, as the price of the load cells and the measuring amplifier has fallen significantly.

II. Measuring amplifier or load cell amplifier
 

The bridge circuit delivers a very small output voltage, which is too low to be processed directly by the microcontroller. Therefore, a measuring amplifier is required to amplify the output signal of the bridge circuit accordingly. Above all, the measuring amplifier should be temperature-independent and low-noise. These two requirements can quickly drive up the price of a measuring amplifier. Most open-source scales use the HX711 load cell amplifier for this task.
 

The HX711 measuring amplifier features a 24-bit analog-to-digital converter integrated into the chip, enabling very high resolution. The HX711 module is sufficiently temperature-stable and low-noise for a beehive scale.

III.) Microcontroller Board
 

The microcontroller board is the heart of every digital online scale, as it processes the incoming signal in program code and forwards the signal. A GSM/GPRS online bee scale requires a microcontroller board with a GSM module. The GSM module can be installed directly on the microcontroller board or plugged onto the board as a so-called shield. Two GSM chips are currently widely used in the Arduino world. These are the SIM800 or SIM900 from SIMCom and the Sara-U2 series from u-blox. The SIM800 or SIM900 are used, for example, in the GBoard from Itead Studio and the Feather 32U4 Fona from Adafruit, and the Sara-U260 or Sara-U270 are used in the Electron from Particle and the Dash board from Hologram.

The microcontroller boards do not just differ in their GSM module, but in many different technical features. For example, for a hive scale that is intended to operate in the open over a longer period of time without an external power supply, power consumption is a crucial feature. Some microcontroller boards already have a charge controller onboard, which allows the battery to be charged via a solar cell. For building your own bee scale, the programming interface and the available libraries are also an important differentiator. The Electron from Particle and the Dash from Hologram, for example, have the option of OTA (Over the Air) programming. Program changes can therefore be made directly via the Internet without a physical connection to the device. These two microcontroller boards are also supplied with a SIM card whose data plan is optimized for Internet of Things applications. A full explanation of the differentiating criteria would go too far here and will be dealt with in a separate article (article to follow).

IV.) Internet Service Provider
 

The services of an internet service provider are also required to transfer data to the internet. The connection to the internet service provider is established via the SIM card. SIM card contracts vary widely in terms of data volume, contract duration, commitment, and costs. National internet service providers generally target their offerings at smartphone customers who want to use high data volumes for as little money as possible. However, for a GSM bee scale that only transmits a value every hour, 1 MB per month is usually sufficient. The rapid rise of Internet of Things applications that require a small amount of data has prompted some internet service providers to offer corresponding data packages. For example, Hologram is not only a manufacturer of the Dash microcontroller board, but also an internet service provider that offers the appropriate data package. Another advantage of the Hologram SIM card is that it can be managed directly online. The Hologram SIM card can be activated and deactivated online at any time. Furthermore, the Hologram dashboard offers easy cost control.

Particle's Electron also comes with a SIM card and can also be managed online.

V.) Data Server - cloud4Bees.at

Finally, we need a way to store and further process the measured data. The cloud4Bees.at data server offers a simple programming interface for storing and reading the measured values ​​in a database. This makes it easy to manage the data and display it graphically. The open programming interface makes it easy to implement program extensions and apps for Android smartphones or iPhones.