Load Cell Weighing Platform

A four-point weighing platform built from scratch: mechanical frame, load cell integration, a custom-designed summing junction board (KiCad), and transmitter calibration.

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Overview

The system measures weight using four load cells mounted at the corners of an aluminium plate. The cells are wired in parallel through a custom junction board, which sums their outputs into a single differential signal. This signal is read by a Baykon TX11 analog weight transmitter, which provides the digital readout and process output.

Platform capacity: 4 kg (4 × 1 kg)
Calibration references: 500 g and 1 kg

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System Architecture

[Load Cell 1] ──┐
[Load Cell 2] ──┤
[Load Cell 3] ──┼──► [Junction Board] ──► [Baykon TX11] ──► Display / Process Output
[Load Cell 4] ──┘      (parallel sum,      (excitation +
                        corner trim)         signal cond.)

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Hardware

Component	Detail
Load cells	4 × single point load cells, 1 kg each, corner-mounted
Transmitter	Baykon TX11, analog input
Junction board	Custom 2-layer PCB, designed in KiCad
Platform	Aluminium plate, 200 × 100 mm
Supply	24 VDC

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Junction Board

The junction board handles three jobs:

1. Excitation distribution — feeds the transmitter's excitation voltage to all four cells in parallel.
2. Signal summing — combines the four differential outputs into a single SIG+/SIG− pair.
3. Corner trimming — series trimmer positions on each cell's signal line, allowing individual corner sensitivity to be balanced.

Schematic and PCB source files are in /kicad.

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Assembly and Wiring

1. Load cells bolted to the four corners of the plate with the specified preload.
2. Individual cell resistances measured and recorded before wiring (input/output bridge resistance checked against datasheet tolerance).
3. Cells wired in parallel via the junction board — EXC+/EXC− common, SIG+/SIG− summed.
4. Shielded cable used between junction board and transmitter, shield grounded at the transmitter end only.

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Calibration

Calibration was performed on the TX11 using 500 g and 1 kg reference weights:

1. Zero (dead load) — platform empty, zero point captured.
2. Span — reference weight applied at plate centre, span calibrated to the known value.
3. Corner test — reference weight moved to each of the four corners in turn; deviation recorded per corner.
4. Linearity check — verified at 500 g and 1 kg, deviation from the ideal line recorded at each point.

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Design Challenges

Corner trimmer resistance mismatch

Corner balancing on a four-cell platform requires trimming resistances in the 10–20 Ω range — the correction needed is a small fraction of the load cell's bridge resistance.

Every trimmer potentiometer available on the local market started at 470 Ω minimum. Fitting one would have made the correction range roughly 25× coarser than required, making fine balancing impossible and risking a large unintended signal offset.

Resolution: the trimmer footprints were kept on the PCB but bridged with 0 Ω links in the first revision, so the board could be tested immediately without waiting on parts. The footprints remain available for a future revision using either low-value multiturn trimmers or fixed precision resistors selected per corner after measurement.

Takeaway: component availability is a design constraint, not an afterthought. Reserving the footprint kept the option open at zero cost instead of forcing a board respin.

Commissioning issues

Bringing the platform from assembled hardware to a trustworthy reading surfaced several issues that had to be resolved in sequence:

Corner deviation. The same reference weight produced different readings depending on which corner it was placed on. This is what drove the corner trimming requirement described above.

Platform rigidity. The plate flexed under load because the mounting surface was not properly fixed. The assembly was taken apart and rebuilt with the mounting positions measured and aligned, which removed the flex and made corner readings repeatable.

Zero drift. The empty-platform reading was not stable. The cause was mechanical stress introduced during assembly — the plate was being loaded by the mounting itself rather than sitting free. Releasing and re-seating the corners removed the residual stress.

Unstable readings. The least significant digit fluctuated continuously under no load. Resolved by adjusting the TX11 filtering and averaging settings.

Transmitter configuration — fault isolation. At one point the excitation voltage parameter would not respond to changes on the TX11, while the mechanical assembly had already been verified. Rather than continuing to troubleshoot the full four-cell system, the platform was stripped down and the transmitter was tested against a single load cell. Isolating the system to its simplest working configuration made the fault visible and allowed the setup to be rebuilt from a known-good baseline.

Working through these in order made one thing clear: on a load cell system the mechanical installation determines the achievable accuracy long before the transmitter settings do.

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Repository Structure

├── kicad/              KiCad schematic and PCB source files
├── platform.jpeg       Assembled platform
├── schematic.png       Junction board schematic
└── README.md

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Tools Used

• KiCad — schematic capture and PCB layout
• SolidWorks — mechanical design of the platform and mounting
• Baykon TX11 — transmitter configuration and calibration

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Author

Habip Can Durmuş — Mechatronics Engineer LinkedIn · [email protected]