OpenScale Applications and Hookup Guide
The SparkFun OpenScale makes reading load cells easy. Attach a four-wire or five-wire load cell of any capacity, plug OpenScale into a USB port, open a terminal window at 9600bps, and you’ll immediately see mass readings. To learn more about load cells see our tutorial on Getting Started with Load Cells. This board also has the Load Cell Combinator built in so you'll be able to read four load sensors as 1 load cell as well.
OpenScale combines the HX711 breakout board with an Atmega328P running Arduino and extensive pre-loaded configuration firmware to create an off-the-shelf solution for load cell reading.
OpenScale was designed for projects and applications where the load was static (for example a bee hive) or where constant readings are needed without user intervention (for example on a conveyor belt system). A load cell with OpenScale can remain in place for months without needing user interaction.
OpenScale makes it easy to zero and calibrate your scale via a simple to use configuration menu. Serial output and control is available through the mini-B USB port or through an FTDI compatible connection. This allows OpenScale to be attached seamlessly with a datalogger (OpenLog) or to a wireless Bluetooth transmitter (such as SparkFun Bluetooth Mate Silver). In the bee scale application , OpenScale is hooked up to Blynk Board and the data collected is pushed to a data-streaming services.
A precision digital temperature sensor is included on OpenScale to report the local temperature. An external connection is also available for a DS18B20 compatible temperature sensor to take temperature readings of the load cell. Please note that OpenScale reports the local and remote temperature readings but it does not alter the scale reading due to temperature fluctuations. It is up to the user to properly calibrate and post process these temperature readings to get the maximum scale accuracy.
OpenScale is fully open source hardware and software. OpenScale comes with a Arduino Uno compatible bootloader (STK500, 115200bps, 16MHz). Making modifications to the firmware is as easy as loading new code onto an Arduino. You can find the all the source in the OpenScale repository on GitHub.
We will just be hooking up a load cell with the OpenScale's HX711 amplifier, and showing how you would hook up four load sensors. To follow along, you'll need:
If you are planning on using load sensors, you will need to obtain or purchase four units to connect the single strain gauges into a wheatstone bridge type load cell. (Single strain gauge load cells only have three wires instead of four.)
If you aren't familiar with the following concepts, we recommend reviewing them before following along with the project example at the end of the tutorial.