The $5 DIY Digital Scale You Can Build Today

Whether you are trying to get the perfect mix for your epoxy or conductive adhesive, or you need to get the thermal compound mixture just right to dissipate heat from a chip you are pushing to its limits, a high-precision scale will come in very handy. However, these scales can be quite expensive. And considering that most of us use them infrequently, we tend to do without them and simply eyeball things to the best of our ability.

There is no need to do that if you are willing to put in a little work, however. As Clive Mitchell has just demonstrated, a highly accurate scale can be hacked together in just a few minutes for under $5. You’ll only need a small number of basic components to get the job done.

In a recent video, Mitchell, an electronics educator and YouTuber, walks viewers through the simple technology that powers many digital scales. At the core of the DIY system he creates are two key parts: a load cell that detects weight and a tiny interface module built around the HX711 load cell amplifier module.

The load cell is composed of carefully engineered pieces of steel. It looks like a simple metal bar with holes drilled through it, but those holes are important to its function. Their size and placement determine how much the metal can flex when weight is applied, which in turn defines the maximum load the sensor can measure—whether that’s one kilogram or twenty.

Attached to this metal structure are strain gauges, zigzag-shaped resistors bonded directly to the surface. When the metal flexes even slightly under load, these gauges stretch as well. That tiny deformation causes a slight change in electrical resistance.

On their own, those resistance changes are extremely small and difficult to measure. That’s where the HX711 module comes in. This inexpensive chip supplies a stable voltage to the load cell, filters out electrical noise, and amplifies the signal coming from the strain gauges. It also includes a high-resolution 24-bit analog-to-digital converter, allowing it to translate minute resistance variations into precise digital readings that are shown on an onboard seven-segment display.

The physical build is straightforward. One end of the load cell is fixed to a base, while the other supports a small platform. When weight is placed on the platform, the metal bends ever so slightly, triggering the strain gauges and producing a measurable signal.

Calibration is also simple. After powering up the module, the user first performs a zero calibration to clear any baseline reading. Then a known reference weight is placed on the platform. Adjustment controls allow the scale’s internal calibration factor to be tuned until the displayed reading matches the reference weight exactly. Once set, those values can be stored in memory so the device remains accurate even after being powered off.

If you want to build your own digital scale at a bargain price, check out the video below for more details.