Load Cell Bricklet¶

Features¶

• Measures output of load cells
• 24bit ADC for high resolution
• Up to 80 weight measurements per second

Description¶

The Load Cell Bricklet can be used to extend the features of Bricks by the capability to measure load cells. Only a single known weight is required to calibrate the load cell. It is possible to measure weight differences of few grams in objects that weigh many kilograms.

Load cells with different maximum weights are available in the shop:

• Load Cell 1kg CZL635
• Load Cell 5kg CZL635
• Load Cell 20kg CZL601
• Load Cell 50kg CZL601

The Bricklet has an LED that can be turned on trough the API, e.g. to show that a weight measurement is in range.

Technical Specifications¶

Resources¶

• HX711 datasheet (Download)
• Schematic (Download)
• Outline and drilling plan (Download)
• Source code and design files (Download)
• 3D model (View online | Download: STEP, FreeCAD)

Connectivity¶

The Load Cell Bricklet has four terminals. The PWR and GND terminals are for the excitation voltage and the IN+ and IN- terminals are for the signal measurement.

A typical load cell will have four or five wires. Check the specification of your load cell for its pinout and connect it according to the table below.

Plugin version 2.0.0 for the Load Cell Bricklet had a bug that resulted in inverted weight measurements. To avoid this you could swap the signal wires connected to the IN+ and IN- terminals. This bug was fixed in version 2.0.1 and the signal wires can be connected according to the table above now.

Test your Load Cell Bricklet¶

To test a Load Cell Bricklet you need to have Brick Daemon and Brick Viewer installed. Brick Daemon acts as a proxy between the USB interface of the Bricks and the API bindings. Brick Viewer connects to Brick Daemon. It helps to figure out basic information about the connected Bricks and Bricklets and allows to test them.

Connect the Load Cell Bricklet to a Brick with a Bricklet Cable. Additionally connect and calibrate a load cell.

If you connect the Brick to the PC over USB, you should see a new tab named "Load Cell Bricklet" in the Brick Viewer after a moment. Select this tab. If everything went as expected you can now see the weight in gram and a graph that shows the weight over time.

After this test you can go on with writing your own application. See the Programming Interface section for the API of the Load Cell Bricklet and examples in different programming languages.

Calibration¶

The Load Cell Bricklet has to be calibrated for the connected load cell and the specific setup.

Connect a load cell to the Bricklet as described above. Then start Brick Viewer and click the "Calibration" button on the "Load Cell Bricklet" tab. With no weight on the load cell, click the "Calibrate Zero" button. Now put a known weight on the load cell, enter the known weight in gram as the "Current Weight", then click the "Calibrate Weight" button.

Now the Load Cell Bricklet is calibrated for the connected load cell and the specific setup.

Scale Kit¶

The Scale Kit is build from MakerBeam, a 1kg Load Cell and laser cut plastic parts. It is available in the Tinkerforge shop, but you can also just use the description to get an idea on how to mount a load cell in general.

• Building up the Scale Kit is pretty easy. Start by removing the protective foil from the plastic parts (there is foil on both sides).
• Screw the 60mm MakerBeam and the load cell to the top plastic part. Ensure to screw the load cell with the arrow side to the plastic part and that the arrow is pointing away from the plastic part.

• Screw the 100mm MakerBeam and the load cell to the bottom plastic part.

• Use the double sided tape to attach the round plate to the 60mm MakerBeam.

• Mechanical construction done! Finally, connect the load cell to the Bricklet as described in the connectivity section.

Case¶

A laser-cut case for the Load Cell Bricklet is available.

The assembly is easiest if you follow the following steps:

• Screw spacers to the Bricklet,
• screw bottom plate to bottom spacers,
• build up side plates,
• plug side plates into bottom plate and
• screw top plate to top spacers.

Below you can see an exploded assembly drawing of the Load Cell Bricklet case:

Hint: There is a protective film on both sides of the plates, you have to remove it before assembly.

Programming Interface¶

See Programming Interface for a detailed description.