LN Tank Scale Creation

Assembling the Feet

LN Scale Wiring Diagram

LN Scale Tape and Rubber Seal Configuration

For each individual scale foot, assemble as follows:

1. Insert the load cell pad into the corresponding hole in the load cell foot and press until snug
2. Insert the load cell 50kg into the load cell rest and press until snug
3. Connect the load cell foot and rest together, lining up the notch in each
4. Place the scale foot into a clamp and tighten until the resistance sharply increases. Avoid over-tightening the clamp, as this could damage the plastic. After, the load cell pad should have a small divot in the center.

Assembling the Scale

1. Arrange the cells as shown in the wiring diagram for the scale and screw into place using the #6 x 113 PH SS screws.
2. Screw the LN scale electronics into place in the center, orienting so that the USB port is on the correct side.

Connecting the Wiring

Connect the black and white wires between the feet before connecting the red wires to the scale electronics. Splice them together as shown below to avoid creating a connection that is prone to catching on things.

1. Slide a 3/32" heat shrink tube onto one of the wires to be spliced. The tube should be about 3/4" long
2. Cut the wire ends so that the connection is long enough to have some give, but not long enough to flop around and cause issues.
3. Strip the wires to about 1/2" from the end (28 gauge wires) and solder them together
4. Fold the connection over on its side so that the stripped ends are flush with one of the wires, then slide the heat shrink over so it covers the soldered ends.
5. Tape the wires down to the scale surface using kapton tape to ensure they stay in place.

LN Scale Before Attaching Top

Connecting the Electronics Assembly

Wire the red wires from the scale feet to the scale electronics assembly, matching the labeled feet to the corresponding bridge port. Solder in place. Attach the 10in USB extension cable to the Pico board and use the 160 cable clamp to screw into place. Use kapton tape to ensure that the cable doesn't curve close to the board, as this could cause the connection to become less stable over time.

Attach the 10in USB extension cable to the Pico board and use the 160 cable clamp to screw into place. Use kapton tape to ensure that the cable doesn't curve close to the board, as this could cause the connection to become less stable over time.

Finishing the Mechanical Assembly

Clean the rubber seal with soap and water before attaching to the edge of the assembly. Use 1.5" strips of double-sided low surface energy tape to attach the seal, spaced evenly around the edge of the scale. Use another strip to adhere the end of the 10in USB extension cable to the edge of the scale as well. FInally, attach 1.5" strips to each pad, but do not remove the backing. Once the tape is attached, slowly lay the seal down and cut the length so that it will fit snugly around the edge while leaving a small space for the 10in cable. There will be a slight gap between the height of the rubber seal and the height of the cable, so use 4-5 strips of tesa tape stacked to make up the difference and ensure a better seal around the edge of the scale.

Downloading and Testing Code

In order to download and test the code, some programs and files must be on the computer beforehand. Thonny must be installed to download the code to the Pico, Serial Port Terminal should be installed to interact with the scale after the code is on the Pico, and Git should ideally be installed to make the code acquisition process easier. The interpreter file for the Pico should also be installed on the computer.

To download the code to the host computer, go to the Aeon Laboratories Github page and download the LN Tank Scale code. It should consist of two files, main.py and hx711.py. Download by cloning the repository with Git, or any other method of choice.

Once the code is downloaded, plug the scale into the host computer with the USB cable. The board should already be in boot mode since it's the first time plugging it in, but if the drive isn't appearing then manually start it in boot mode by holding the reset button on the board while plugging it in. Once the drive appears, copy the interpreter over to it in file explorer, which should restart the device.

Use Thonny to open the two files, and make sure to select the correct device in the bottom right of the window. The correct one is called Micropython(Raspberry Pi Pico), not Micropython(RP2040). Download the hx711.py to the Pico. If you want to test the code, run the main on the computer before downloading to the Pico to make sure it's running properly. Relevant commands include: z - displays the device name, the date of the code's last change, and the free memory on the Pico g [g1] [g2] - displays the gain, or sets the gain for each bridge amp. Omitting g2 causes g1 to be used for both amps. r [i] - displays a reading from the scale, or sets the output to display a reading on an interval of i seconds. h - displays a header showing the meaning of each value of the scale's readings shutdown - shuts down the board

Once the code is verified to be working correctly, download main.py onto the Pico using Thonny, then close Thonny. From this point onward, use the serial port terminal to interact with the board (turn CRC codes off beforehand). If necessary, unplug and re-plug the board in to re-initialize the code. Also, be aware of a bug in the serial port terminal program that causes the wrong COM port to be used. If the COM ports in the program and in the program window's header (upper left corner) don't match, select the proper COM port and click the reset button in the bottom right corner.

Finishing the Scale

Once the code is downloaded and tested, the lid can be attached.