Build a Digital Kitchen Scale with Arduino Uno and a Load Cell
A DIY digital kitchen scale works by converting a physical bend into a number: a load cell — a small metal bar with strain gauges bonded to it — flexes by a few micrometers under the weight of whatever sits on the platform, and that flex changes the electrical resistance across the gauges by a tiny, otherwise unreadable amount. The HX711 amplifier module sits between the load cell and the microcontroller specifically to solve that unreadable-amount problem: it boosts the signal and converts it to a digital value an Arduino can read over two dedicated pins, one for data and one for a clock signal. The Arduino then applies a calibration factor to turn that raw number into grams and pushes it to a small screen. Every part of that chain — load cell, amplifier, microcontroller, display — has to agree on wiring and calibration before the number on the screen means anything.
What parts does a digital kitchen scale need?
At minimum: a load cell to sense weight, an HX711 amplifier module because the load cell's raw signal is too weak for a microcontroller to read directly, a microcontroller such as an Arduino Uno to run the calibration math, a small display to show the result, jumper wires, and a power source. That's five active components in total, plus wiring — there's no separate "scale" chip; the load cell and HX711 do the sensing, and everything else is the same general-purpose hardware used in most beginner electronics builds.
How does a load cell measure weight?
A load cell is a machined metal bar (usually aluminum) with four strain gauges bonded to it in a Wheatstone bridge arrangement. When weight bends the bar, two gauges stretch and two compress, unbalancing the bridge and producing a tiny voltage difference proportional to the load — typically on the order of millivolts, far too small for an Arduino's analog input to resolve usefully on its own. That's the entire reason the HX711 exists: it's a 24-bit analog-to-digital converter built specifically for load cell bridges, amplifying that millivolt-level signal and outputting a clean digital reading over two pins. A load cell alone, wired straight to a microcontroller, will not produce a usable weight reading.
How do you calibrate a DIY scale for accuracy?
Calibration means telling the firmware what "zero" looks like and what a known weight looks like, then computing a scale factor between the two. In practice: power the scale up with nothing on the platform and record the HX711's raw reading as the zero offset (tare), then place an object of known weight — a bag of sugar you've verified on another scale, or a set of calibration weights — on the platform and record the new raw reading. The difference between the two readings, divided by the known weight, gives the calibration factor the firmware multiplies future readings by. Skip this step and the display will still show a number, but it won't correspond to real grams. Compoden's storefront assistant flagged this directly when it carded this build's parts: "load cell calibration" and "incorrect wiring, especially with the load cell amplifier" were the two problems it named as most common on this exact build.
What weight capacity load cell should you pick?
Load cell capacity should roughly match what you intend to weigh, not exceed it by a wide margin — a 50kg load cell reading a 200g spice measurement is working at less than 1% of its rated range, which costs resolution. Compoden's catalog carries 1kg, 5kg, 10kg, and 50kg strain-gauge load cells at ₹140, ₹150, ₹130, and ₹45 respectively. For a kitchen scale meant to weigh ingredients (grams up to a few kilograms), the 1kg or 5kg option gives finer resolution than the 50kg cell that Compoden's assistant defaulted to below; if you also want to weigh larger stock pots or bulk ingredients, the 10kg or 50kg cell trades resolution for headroom. All four use the same four-wire bridge output and wire to the HX711 identically, so swapping capacity later doesn't change anything else in the build.
How do you wire the HX711 and display to an Arduino Uno?
The HX711 needs two separate digital pins on the Arduino — one for data, one for a clock signal — because it communicates over a simple two-wire serial protocol, not a single line. A build with only one of those two pins connected cannot read anything; both are required. Here's the correct wiring for this build, using DT on pin 2 and SCK on pin 3:
| Arduino Uno | HX711 module | Signal |
|---|---|---|
| 5V | VCC | power |
| GND | GND | ground |
| D2 | DT (DOUT) | data, out of HX711 |
| D3 | SCK | clock, into HX711 |
| Load cell wire | HX711 terminal | Signal |
|---|---|---|
| Excitation + | E+ | bridge power |
| Excitation – | E– | bridge ground |
| Signal + | A+ | bridge output + |
| Signal – | A– | bridge output – |
| Arduino Uno | Display (I2C) | Signal |
|---|---|---|
| 5V | VCC | power |
| GND | GND | ground |
| A4 | SDA | I2C data |
| A5 | SCL | I2C clock |
The load cell's four bridge wires go to the HX711's screw terminals, not to the Arduino directly — the Arduino only ever talks to the HX711. Compoden's own build assistant separately flagged a real voltage mismatch worth knowing before wiring: some I2C displays run 3.3V logic while the Uno's I2C bus is 5V, which "can cause problems if not handled correctly, potentially damaging the display or preventing communication" — check your specific display's logic voltage before connecting it directly.
Watch it built live: a real Arduino Uno + load cell project
Rather than describe a generic build, we typed one real sentence into Compoden's AI build assistant on the storefront and let it pick parts, price them, and explain the build — unscripted, screenshotted as it happened:
"I want to build a digital kitchen scale with a display using an Arduino Uno and a load cell"
It carded six in-stock parts: an Arduino Uno, a 50kg load cell, an HX711 amplifier module, a 0.96 inch I2C OLED display, a 5V 2A power adapter, and jumper wires. On the amplifier, it explained: "The HX711 Load Cell Amplifier Module is needed because the signal from the load cell is too weak for the microcontroller to read directly. This module takes the tiny analog signal from the load cell and amplifies it, making it much stronger and converting it into a digital signal." It also estimated total current draw at roughly 110mA and named the two failure modes it considered most likely on this build up front: "problems with the load cell calibration, where the scale gives inconsistent or incorrect readings if not set up properly," and "incorrect wiring, especially with the load cell amplifier, which can lead to no readings or unstable readings."
Watch the firmware get generated
We then asked Compoden's build companion, Soldr, to write the actual Arduino sketch for this project — targeting the Uno specifically, reading the load cell through the HX711 and showing the result on a display:
The generated sketch wired the HX711's DT to digital pin 2 and SCK to digital pin 3 — two separate pins, exactly as the two-wire protocol requires — and the display over I2C on A4 (SDA) and A5 (SCL), with a starting calibration factor of -22000.0 that Soldr was explicit needs adjusting: "you will need to calibrate this value for your specific load cell by placing a known weight on it and adjusting the calibration_factor until the displayed weight is accurate." Soldr also flagged, before letting the code be flashed, that no parts were carded in that session to check the wiring against: "nothing is in your build yet, so this code has not been checked against any board. I could not verify the pins or compile it." That caveat is exactly why the wiring table above — matched against the actual parts this build carded on the storefront — is the one to build from, not a substitute for it.
Who this build is for
This is a reasonable first sensor project for someone who has already wired at least one basic Arduino circuit and wants to move beyond blinking an LED into reading and displaying a real physical measurement. The parts count is small, none of the wiring is exotic, and the one genuinely fiddly step — calibration — is a repeatable procedure rather than trial and error. It's not a plug-and-play kitchen tool; expect to spend time getting the calibration factor right before the numbers on the display are trustworthy.
Get everything in this build
The six parts Compoden's assistant picked above, at today's live price and stock — each links straight to checkout, or add the whole tray in one click.
| Part | Qty | Price | |
|---|---|---|---|
| Arduino Uno R3 CH340G ATmega328P Board | 1 | ₹230 | Add to cart → |
| 50kg Load Cell (Strain Gauge) | 1 | ₹45 | Add to cart → |
| HX711 Load Cell Amplifier Module | 1 | ₹120 | Add to cart → |
| 0.96 inch OLED Display Module 128x64 I2C Yellow/Blue (SSD1306) | 1 | ₹246 | Add to cart → |
| 5V 2A Micro-USB Power Adapter | 1 | ₹140 | Add to cart → |
| Male-to-Male Breadboard Jumper Wires (20cm, 24 AWG) | 1 | ₹40 | Add to cart → |
| Total | ₹821 | Add all 6 to cart → |
Prices and stock verified live at the time this was written; Compoden's storefront always reflects the current price at checkout. Swap the 50kg load cell for the 1kg or 5kg option in the catalog if you're weighing small kitchen quantities and want finer resolution — the wiring above doesn't change.
Built and Backed by Compoden
Every part above ships from Compoden's own India stock, tested for compatibility before it's carded together — not sourced individually and hoped to work. Delivery in 3–7 days across India, with COD and UPI available at checkout. If a part in this build doesn't perform as described, Compoden's support team will help you troubleshoot or replace it.
FAQ
Why does the HX711 need two Arduino pins instead of one?
It communicates using a simple two-wire serial protocol: one pin (SCK) is a clock signal the Arduino sends to the HX711, and the other (DT/DOUT) is the data the HX711 sends back in response to each clock pulse. With only one pin connected, there's no clock to trigger a data transfer, so no reading is possible. Both DT and SCK must go to separate, distinct digital pins — pins 2 and 3 in this build.
Can I use a different load cell capacity than the 50kg one shown here?
Yes, and for a kitchen scale it's usually a better choice. Compoden also carries 1kg, 5kg, and 10kg strain-gauge load cells that wire to the HX711 identically; a lower-capacity cell gives finer resolution for the small quantities a kitchen scale typically weighs.
Why does my scale show a random number the moment it powers on?
That's the HX711's raw, uncalibrated reading before any tare or calibration factor has been applied in firmware. It's expected on first power-up and goes away once the sketch tares the scale (zeroing it with nothing on the platform) and a calibration factor has been set for grams.
Does the display need different power than the Arduino Uno?
It depends on the specific display. Some I2C displays run 3.3V logic while the Arduino Uno's I2C bus runs at 5V; connecting a 3.3V-only display directly to the Uno's 5V I2C lines can damage it or cause unreliable communication, so check your display's rated logic voltage before wiring it.