An Arduino\u2019s analog input resolves about 5 millivolts, which is roughly a thousand times too coarse to see anything at all. The HX711 is the bridge. It is a 24-bit converter built specifically for load cells, with a built-in amplifier, and it turns those microvolts into numbers you can work with.<\/p>\n
This is the most precise measurement in the library, and the one that most depends on doing the calibration properly.<\/p>\n
Before you begin<\/h2>\nRequired parts and tools<\/h3>\n\n- An Arduino Uno or compatible board.<\/li>\n
- One HX711 module. This is Siratek product 2881.<\/li>\n
- A load cell, which is not included.<\/strong> Buy one rated a little above the heaviest thing you mean to weigh.<\/li>\n
- A soldering iron. The supplied ten-pin header is loose and must be soldered on.<\/strong><\/li>\n
- Something rigid to mount the cell on, and a known weight for calibration.<\/li>\n<\/ul>\n
The board has two sides<\/h3>\n
The green board is marked clearly:<\/p>\n
\nJ1<\/code><\/strong>, the load cell side: E+ E- A- A+ B- B+<\/code><\/strong><\/li>\nJP2<\/code><\/strong>, the Arduino side: GND DT SCK VCC<\/code><\/strong><\/li>\n<\/ul>\nE+<\/code> and E-<\/code> excite the load cell. A-<\/code> and A+<\/code> are the measurement input, channel A. B-<\/code> and B+<\/code> are a second channel at lower gain, which you can ignore for a single cell.<\/p>\nWiring the load cell<\/h3>\n
A four-wire load cell almost always uses these colours:<\/p>\n
\n\n\nWire<\/th>\n To<\/th>\n Meaning<\/th>\n<\/tr>\n<\/thead>\n \n\nRed<\/td>\n E+<\/code><\/td>\nExcitation positive<\/td>\n<\/tr>\n \nBlack<\/td>\n E-<\/code><\/td>\nExcitation negative<\/td>\n<\/tr>\n \nWhite<\/td>\n A-<\/code><\/td>\nSignal negative<\/td>\n<\/tr>\n \nGreen<\/td>\n A+<\/code><\/td>\nSignal positive<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nWhite and green are the pair that varies between manufacturers. If pressing down makes the reading go more negative, swap those two.<\/strong> Nothing is harmed by getting it wrong; the sign simply inverts.<\/p>\nSome cells have a fourth colour, often yellow, which is a shield. Connect it to GND<\/code> or leave it; do not put it on a signal pin.<\/p>\nMounting matters more than the electronics<\/h3>\n
This is the part people skip, and it is why a working circuit gives useless numbers.<\/p>\n
A bar load cell is designed to be clamped at one end and loaded at the other<\/strong>, with the middle free to flex. The arrow on its side shows the direction the force should act.<\/p>\n\n- Bolt one end to something solid.<\/strong> A cell held in the hand measures your hand.<\/li>\n
- Load the other end through a platform<\/strong>, with spacers so the cell can bend. If the platform touches the base anywhere else, the force bypasses the cell and the reading goes nowhere.<\/li>\n
- Keep the load central.<\/strong> Weight at the far corner of a wide platform reads differently from the same weight in the middle. That is not drift; it is the cell being bent in a way it was not designed for.<\/li>\n<\/ul>\n
Spend the time on the mechanics. A perfectly calibrated cell mounted badly is worse than useless, because it looks right.<\/p>\n
Two numbers you must find<\/h3>\n
Every load cell and every mounting produces its own two constants.<\/p>\n
The offset<\/strong>, or tare: what the system reads with nothing on it. This is not zero, and it changes if you move the platform or tighten a bolt.<\/p>\nThe scale factor<\/strong>: how many raw counts correspond to one gram. This depends on the cell\u2019s rating, the HX711\u2019s gain and your mounting.<\/p>\nNeither can be looked up. Both must be measured, with the procedure below, and both must be measured again if you change the mechanics in any way<\/strong>.<\/p>\nIt is slow, and that is fine<\/h3>\n
The HX711 runs at 10 samples a second, or 80 if a pin on the chip is tied differently. Ten is plenty for a scale, and the slower rate is quieter.<\/p>\n
It is also not SPI and not I2C, despite having a clock and a data pin. It is its own simple protocol, which the library bit-bangs, so any two digital pins work.<\/p>\n
Pin reference<\/h2>\n
\n\n\nModule pin<\/th>\n Connect to<\/th>\n Purpose<\/th>\n<\/tr>\n<\/thead>\n \n\nGND<\/code><\/td>\nUno GND<\/code><\/td>\nGround<\/td>\n<\/tr>\n \nDT<\/code><\/td>\nUno D3<\/code><\/td>\nData out of the HX711<\/td>\n<\/tr>\n \nSCK<\/code><\/td>\nUno D2<\/code><\/td>\nClock from the Arduino<\/td>\n<\/tr>\n \nVCC<\/code><\/td>\nUno 5V<\/code><\/td>\nPower<\/td>\n<\/tr>\n \nE+<\/code> E-<\/code> A-<\/code> A+<\/code><\/td>\nThe load cell<\/td>\n Red, black, white, green<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n![\"An](\"http:\/\/siratek.net\/wp-content\/uploads\/2026\/11\/hx711-load-cell-wiring.svg\")
The electronics are the easy half. How the cell is clamped decides whether the numbers mean anything.<\/figcaption><\/figure>\nWiring steps<\/h2>\n\n- Unplug the USB cable.<\/li>\n
- Solder the ten-pin header to the board.<\/li>\n
- Solder or screw the load cell\u2019s four wires to
E+<\/code>, E-<\/code>, A-<\/code>, A+<\/code> by colour.<\/li>\nGND<\/code> to GND<\/code>, VCC<\/code> to 5V<\/code>.<\/li>\nDT<\/code> to D3<\/code>, SCK<\/code> to D2<\/code>.<\/li>\n- Mount the cell properly before taking it seriously.<\/li>\n
- Plug the USB cable back in.<\/li>\n<\/ol>\n
Software and libraries<\/h2>\n
Install HX711<\/strong> by Bogdan Necula, or the similarly named library by Rob Tillaart. The sketches below use the first. Record which one, because their method names differ.<\/p>\nMinimal working example<\/h2>\n
Start with raw counts. They look meaningless and they are exactly what you need.<\/p>\n
\/\/ Siratek: raw readings. Press on the platform and watch the numbers.\n\n#include \"HX711.h\"\n\nconst int dataPin = 3;\nconst int clockPin = 2;\n\nHX711 scale;\n\nvoid setup() {\n Serial.begin(9600);\n scale.begin(dataPin, clockPin);\n Serial.println(\"Siratek: raw counts. Press down and see which way they move.\");\n}\n\nvoid loop() {\n if (scale.is_ready()) {\n Serial.println(scale.read());\n } else {\n Serial.println(\"HX711 not ready. Check DT, SCK and power.\");\n }\n delay(500);\n}<\/code><\/pre>\nThree things to check here, in order.<\/p>\n
Does it say \u201cnot ready\u201d?<\/strong> Then the wiring is wrong, and nothing else will work.<\/p>\nDo the numbers change when you press?<\/strong> If not, the load cell wiring or the mounting is at fault, not the board.<\/p>\nDo they go up when you press down?<\/strong> If they go down, swap the white and green wires.<\/p>\nCalibration<\/h3>\n
Now the two constants. This is the part that turns counts into grams.<\/p>\n
\/\/ Siratek: find the offset and the scale factor for YOUR cell and mounting.\n\/\/ Follow the prompts. Write both numbers down.\n\n#include \"HX711.h\"\n\nHX711 scale;\n\n\/\/ The weight of the object you will use. Measure it on a kitchen scale.\nconst float knownGrams = 500.0;\n\nvoid setup() {\n Serial.begin(9600);\n while (!Serial) {\n ;\n }\n\n scale.begin(3, 2);\n\n Serial.println(\"Siratek: remove everything from the platform, then send any character.\");\n while (Serial.available() == 0) {\n delay(50);\n }\n while (Serial.available()) {\n Serial.read();\n }\n\n scale.tare(20); \/\/ average twenty readings for the zero\n long offset = scale.get_offset();\n Serial.print(\"offset = \");\n Serial.println(offset);\n\n Serial.print(\"Now put the \");\n Serial.print(knownGrams, 0);\n Serial.println(\" g weight on, then send any character.\");\n while (Serial.available() == 0) {\n delay(50);\n }\n\n long loaded = scale.get_value(20); \/\/ averaged, with the offset removed\n float factor = loaded \/ knownGrams;\n\n Serial.print(\"raw with weight = \");\n Serial.println(loaded);\n Serial.print(\"scale factor = \");\n Serial.println(factor, 4);\n Serial.println();\n Serial.println(\"Put both numbers into the weighing sketch.\");\n}\n\nvoid loop() {\n}<\/code><\/pre>\nUse the heaviest weight you can that is still within the cell\u2019s rating. Calibrating a 5 kg cell with a 20 g weight gives a factor dominated by noise.<\/p>\n
A litre of water is a kilogram, near enough, and most people have a bottle.<\/p>\n
Weighing<\/h3>\n\/\/ Siratek: a scale, using the two numbers you measured.\n\n#include \"HX711.h\"\n\nHX711 scale;\n\n\/\/ From the calibration sketch. Yours will differ, and they are not optional.\nconst long myOffset = 0;\nconst float myFactor = 1.0;\n\nvoid setup() {\n Serial.begin(9600);\n scale.begin(3, 2);\n\n scale.set_offset(myOffset);\n scale.set_scale(myFactor);\n\n Serial.println(\"Siratek: scale ready.\");\n}\n\nvoid loop() {\n \/\/ Average ten readings. A single one jumps around by a gram or two.\n float grams = scale.get_units(10);\n\n Serial.print(grams, 1);\n Serial.println(\" g\");\n\n delay(500);\n}<\/code><\/pre>\nAveraging ten readings is the difference between a scale and a random number generator. At this resolution the last digit is always moving, and the eye reads a jittering display as broken even when the average is correct.<\/p>\n
Drift, and why a tare button is worth adding<\/h3>\n
Leave a calibrated scale running and the zero wanders, by a gram or two over an hour. Strain gauges are temperature sensitive, and the metal itself relaxes.<\/p>\n
Real scales handle this by taring every time you use them, and so should yours: a button that calls scale.tare()<\/code> costs one pin and removes the problem entirely.<\/p>\nif (digitalRead(tareButton) == LOW) {\n scale.tare(20);\n Serial.println(\"tared\");\n}<\/code><\/pre>\nExpected result<\/h2>\n
Raw counts that move clearly when you press on the platform, and after calibration, a weight in grams accurate to a gram or two with a stable reading.<\/p>\n
Put the known weight back on and check it reads what it should. Then put it in a different place on the platform and check again: a large difference tells you about the mounting, not the electronics.<\/p>\n
Troubleshooting<\/h2>\n
\n\n\nSymptom<\/th>\n Likely cause<\/th>\n Check or fix<\/th>\n<\/tr>\n<\/thead>\n \n\n\u201cnot ready\u201d forever<\/td>\n DT<\/code> and SCK<\/code> swapped, or no power<\/td>\nCheck all four Arduino wires<\/td>\n<\/tr>\n \nRaw value never changes<\/td>\n Load cell wiring, or bad mounting<\/td>\n Check colours, then the mechanics<\/td>\n<\/tr>\n \nReading goes down when you press<\/td>\n Signal pair reversed<\/td>\n Swap white and green<\/td>\n<\/tr>\n \nWildly fluctuating raw values<\/td>\n A load cell wire not connected<\/td>\n Reseat; check solder joints<\/td>\n<\/tr>\n \nWeight roughly right but out by a factor<\/td>\n Wrong scale factor<\/td>\n Recalibrate with a known weight<\/td>\n<\/tr>\n \nReads zero no matter what<\/td>\n set_scale()<\/code> with the default<\/td>\nPut your own factor in<\/td>\n<\/tr>\n \nZero wanders over an hour<\/td>\n Temperature and metal relaxation<\/td>\n Normal; add a tare button<\/td>\n<\/tr>\n \nDifferent reading at the platform\u2019s edge<\/td>\n Off-centre loading<\/td>\n Expected; load centrally<\/td>\n<\/tr>\n \nChanged after tightening a bolt<\/td>\n Mechanics changed<\/td>\n Recalibrate<\/td>\n<\/tr>\n \nReading saturates under load<\/td>\n Cell over its rating<\/td>\n Use a cell rated above your maximum<\/td>\n<\/tr>\n \nNoisy near a motor<\/td>\n Microvolt signals pick up interference<\/td>\n Separate the supplies; keep leads short<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nNext steps<\/h2>\n\n- Easier first:<\/strong> Digital and Analog, and When Each Applies<\/em>, for why an analog pin cannot do this.<\/li>\n
- Related products:<\/strong> a 16\u00d72 LCD to show the weight, and a push button for tare.<\/li>\n
- Next project:<\/strong> a kitchen scale with a display and a tare button, which is a genuinely useful object rather than a demonstration.<\/li>\n<\/ul>\n
Sources and attribution<\/h2>\n
All text, wiring guidance and code in this tutorial are original Siratek work.<\/p>\n
\n- HX711 datasheet for the 24-bit conversion, the sample rates and the channel arrangement.<\/li>\n
- The
E+ E- A- A+ B- B+<\/code> and GND DT SCK VCC<\/code> headers and the loose ten-pin header were read from the Siratek product photographs for item 2881. The same photographs show the board supplied without a load cell, which is why one appears in the parts list.<\/li>\n<\/ul>\nLoad cell wire colours are near-universal but not guaranteed, so the tutorial gives a test rather than asserting them. Offset and scale factor are presented as values the reader must measure, as they depend on the individual cell and its mounting. No third-party tutorial text, diagrams, photographs or code has been reproduced here.<\/p>\n
<\/p>\n<\/body>","protected":false},"excerpt":{"rendered":"
A load cell is a piece of metal that bends very slightly under weight, with strain gauges bonded to it that change resistance as it bends. The change is tiny: a few microvolts per gram.<\/p>\n","protected":false},"featured_media":0,"template":"","siratek_tutorial_level":[],"class_list":["post-52257","siratek_tutorial","type-siratek_tutorial","status-publish","hentry"],"yoast_head":"\n
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- \n
- An Arduino Uno or compatible board.<\/li>\n
- One HX711 module. This is Siratek product 2881.<\/li>\n
- A load cell, which is not included.<\/strong> Buy one rated a little above the heaviest thing you mean to weigh.<\/li>\n
- A soldering iron. The supplied ten-pin header is loose and must be soldered on.<\/strong><\/li>\n
- Something rigid to mount the cell on, and a known weight for calibration.<\/li>\n<\/ul>\n
The board has two sides<\/h3>\n
The green board is marked clearly:<\/p>\n
- \n
J1<\/code><\/strong>, the load cell side:E+ E- A- A+ B- B+<\/code><\/strong><\/li>\nJP2<\/code><\/strong>, the Arduino side:GND DT SCK VCC<\/code><\/strong><\/li>\n<\/ul>\nE+<\/code> andE-<\/code> excite the load cell.A-<\/code> andA+<\/code> are the measurement input, channel A.B-<\/code> andB+<\/code> are a second channel at lower gain, which you can ignore for a single cell.<\/p>\nWiring the load cell<\/h3>\n
A four-wire load cell almost always uses these colours:<\/p>\n
\n\n
\n \nWire<\/th>\n To<\/th>\n Meaning<\/th>\n<\/tr>\n<\/thead>\n \n Red<\/td>\n E+<\/code><\/td>\nExcitation positive<\/td>\n<\/tr>\n \n Black<\/td>\n E-<\/code><\/td>\nExcitation negative<\/td>\n<\/tr>\n \n White<\/td>\n A-<\/code><\/td>\nSignal negative<\/td>\n<\/tr>\n \n Green<\/td>\n A+<\/code><\/td>\nSignal positive<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n White and green are the pair that varies between manufacturers. If pressing down makes the reading go more negative, swap those two.<\/strong> Nothing is harmed by getting it wrong; the sign simply inverts.<\/p>\n
Some cells have a fourth colour, often yellow, which is a shield. Connect it to
GND<\/code> or leave it; do not put it on a signal pin.<\/p>\nMounting matters more than the electronics<\/h3>\n
This is the part people skip, and it is why a working circuit gives useless numbers.<\/p>\n
A bar load cell is designed to be clamped at one end and loaded at the other<\/strong>, with the middle free to flex. The arrow on its side shows the direction the force should act.<\/p>\n
- \n
- Bolt one end to something solid.<\/strong> A cell held in the hand measures your hand.<\/li>\n
- Load the other end through a platform<\/strong>, with spacers so the cell can bend. If the platform touches the base anywhere else, the force bypasses the cell and the reading goes nowhere.<\/li>\n
- Keep the load central.<\/strong> Weight at the far corner of a wide platform reads differently from the same weight in the middle. That is not drift; it is the cell being bent in a way it was not designed for.<\/li>\n<\/ul>\n
Spend the time on the mechanics. A perfectly calibrated cell mounted badly is worse than useless, because it looks right.<\/p>\n
Two numbers you must find<\/h3>\n
Every load cell and every mounting produces its own two constants.<\/p>\n
The offset<\/strong>, or tare: what the system reads with nothing on it. This is not zero, and it changes if you move the platform or tighten a bolt.<\/p>\n
The scale factor<\/strong>: how many raw counts correspond to one gram. This depends on the cell\u2019s rating, the HX711\u2019s gain and your mounting.<\/p>\n
Neither can be looked up. Both must be measured, with the procedure below, and both must be measured again if you change the mechanics in any way<\/strong>.<\/p>\n
It is slow, and that is fine<\/h3>\n
The HX711 runs at 10 samples a second, or 80 if a pin on the chip is tied differently. Ten is plenty for a scale, and the slower rate is quieter.<\/p>\n
It is also not SPI and not I2C, despite having a clock and a data pin. It is its own simple protocol, which the library bit-bangs, so any two digital pins work.<\/p>\n
Pin reference<\/h2>\n
\n\n
\n \nModule pin<\/th>\n Connect to<\/th>\n Purpose<\/th>\n<\/tr>\n<\/thead>\n \n GND<\/code><\/td>\nUno GND<\/code><\/td>\nGround<\/td>\n<\/tr>\n \n DT<\/code><\/td>\nUno D3<\/code><\/td>\nData out of the HX711<\/td>\n<\/tr>\n \n SCK<\/code><\/td>\nUno D2<\/code><\/td>\nClock from the Arduino<\/td>\n<\/tr>\n \n VCC<\/code><\/td>\nUno 5V<\/code><\/td>\nPower<\/td>\n<\/tr>\n \n E+<\/code>E-<\/code>A-<\/code>A+<\/code><\/td>\nThe load cell<\/td>\n Red, black, white, green<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n The electronics are the easy half. How the cell is clamped decides whether the numbers mean anything.<\/figcaption><\/figure>\n Wiring steps<\/h2>\n
- \n
- Unplug the USB cable.<\/li>\n
- Solder the ten-pin header to the board.<\/li>\n
- Solder or screw the load cell\u2019s four wires to
E+<\/code>,E-<\/code>,A-<\/code>,A+<\/code> by colour.<\/li>\nGND<\/code> toGND<\/code>,VCC<\/code> to5V<\/code>.<\/li>\nDT<\/code> toD3<\/code>,SCK<\/code> toD2<\/code>.<\/li>\n- Mount the cell properly before taking it seriously.<\/li>\n
- Plug the USB cable back in.<\/li>\n<\/ol>\n
Software and libraries<\/h2>\n
Install HX711<\/strong> by Bogdan Necula, or the similarly named library by Rob Tillaart. The sketches below use the first. Record which one, because their method names differ.<\/p>\n
Minimal working example<\/h2>\n
Start with raw counts. They look meaningless and they are exactly what you need.<\/p>\n
\/\/ Siratek: raw readings. Press on the platform and watch the numbers.\n\n#include \"HX711.h\"\n\nconst int dataPin = 3;\nconst int clockPin = 2;\n\nHX711 scale;\n\nvoid setup() {\n Serial.begin(9600);\n scale.begin(dataPin, clockPin);\n Serial.println(\"Siratek: raw counts. Press down and see which way they move.\");\n}\n\nvoid loop() {\n if (scale.is_ready()) {\n Serial.println(scale.read());\n } else {\n Serial.println(\"HX711 not ready. Check DT, SCK and power.\");\n }\n delay(500);\n}<\/code><\/pre>\nThree things to check here, in order.<\/p>\n
Does it say \u201cnot ready\u201d?<\/strong> Then the wiring is wrong, and nothing else will work.<\/p>\n
Do the numbers change when you press?<\/strong> If not, the load cell wiring or the mounting is at fault, not the board.<\/p>\n
Do they go up when you press down?<\/strong> If they go down, swap the white and green wires.<\/p>\n
Calibration<\/h3>\n
Now the two constants. This is the part that turns counts into grams.<\/p>\n
\/\/ Siratek: find the offset and the scale factor for YOUR cell and mounting.\n\/\/ Follow the prompts. Write both numbers down.\n\n#include \"HX711.h\"\n\nHX711 scale;\n\n\/\/ The weight of the object you will use. Measure it on a kitchen scale.\nconst float knownGrams = 500.0;\n\nvoid setup() {\n Serial.begin(9600);\n while (!Serial) {\n ;\n }\n\n scale.begin(3, 2);\n\n Serial.println(\"Siratek: remove everything from the platform, then send any character.\");\n while (Serial.available() == 0) {\n delay(50);\n }\n while (Serial.available()) {\n Serial.read();\n }\n\n scale.tare(20); \/\/ average twenty readings for the zero\n long offset = scale.get_offset();\n Serial.print(\"offset = \");\n Serial.println(offset);\n\n Serial.print(\"Now put the \");\n Serial.print(knownGrams, 0);\n Serial.println(\" g weight on, then send any character.\");\n while (Serial.available() == 0) {\n delay(50);\n }\n\n long loaded = scale.get_value(20); \/\/ averaged, with the offset removed\n float factor = loaded \/ knownGrams;\n\n Serial.print(\"raw with weight = \");\n Serial.println(loaded);\n Serial.print(\"scale factor = \");\n Serial.println(factor, 4);\n Serial.println();\n Serial.println(\"Put both numbers into the weighing sketch.\");\n}\n\nvoid loop() {\n}<\/code><\/pre>\nUse the heaviest weight you can that is still within the cell\u2019s rating. Calibrating a 5 kg cell with a 20 g weight gives a factor dominated by noise.<\/p>\n
A litre of water is a kilogram, near enough, and most people have a bottle.<\/p>\n
Weighing<\/h3>\n
\/\/ Siratek: a scale, using the two numbers you measured.\n\n#include \"HX711.h\"\n\nHX711 scale;\n\n\/\/ From the calibration sketch. Yours will differ, and they are not optional.\nconst long myOffset = 0;\nconst float myFactor = 1.0;\n\nvoid setup() {\n Serial.begin(9600);\n scale.begin(3, 2);\n\n scale.set_offset(myOffset);\n scale.set_scale(myFactor);\n\n Serial.println(\"Siratek: scale ready.\");\n}\n\nvoid loop() {\n \/\/ Average ten readings. A single one jumps around by a gram or two.\n float grams = scale.get_units(10);\n\n Serial.print(grams, 1);\n Serial.println(\" g\");\n\n delay(500);\n}<\/code><\/pre>\nAveraging ten readings is the difference between a scale and a random number generator. At this resolution the last digit is always moving, and the eye reads a jittering display as broken even when the average is correct.<\/p>\n
Drift, and why a tare button is worth adding<\/h3>\n
Leave a calibrated scale running and the zero wanders, by a gram or two over an hour. Strain gauges are temperature sensitive, and the metal itself relaxes.<\/p>\n
Real scales handle this by taring every time you use them, and so should yours: a button that calls
scale.tare()<\/code> costs one pin and removes the problem entirely.<\/p>\nif (digitalRead(tareButton) == LOW) {\n scale.tare(20);\n Serial.println(\"tared\");\n}<\/code><\/pre>\nExpected result<\/h2>\n
Raw counts that move clearly when you press on the platform, and after calibration, a weight in grams accurate to a gram or two with a stable reading.<\/p>\n
Put the known weight back on and check it reads what it should. Then put it in a different place on the platform and check again: a large difference tells you about the mounting, not the electronics.<\/p>\n
Troubleshooting<\/h2>\n
\n\n
\n \nSymptom<\/th>\n Likely cause<\/th>\n Check or fix<\/th>\n<\/tr>\n<\/thead>\n \n \u201cnot ready\u201d forever<\/td>\n DT<\/code> andSCK<\/code> swapped, or no power<\/td>\nCheck all four Arduino wires<\/td>\n<\/tr>\n \n Raw value never changes<\/td>\n Load cell wiring, or bad mounting<\/td>\n Check colours, then the mechanics<\/td>\n<\/tr>\n \n Reading goes down when you press<\/td>\n Signal pair reversed<\/td>\n Swap white and green<\/td>\n<\/tr>\n \n Wildly fluctuating raw values<\/td>\n A load cell wire not connected<\/td>\n Reseat; check solder joints<\/td>\n<\/tr>\n \n Weight roughly right but out by a factor<\/td>\n Wrong scale factor<\/td>\n Recalibrate with a known weight<\/td>\n<\/tr>\n \n Reads zero no matter what<\/td>\n set_scale()<\/code> with the default<\/td>\nPut your own factor in<\/td>\n<\/tr>\n \n Zero wanders over an hour<\/td>\n Temperature and metal relaxation<\/td>\n Normal; add a tare button<\/td>\n<\/tr>\n \n Different reading at the platform\u2019s edge<\/td>\n Off-centre loading<\/td>\n Expected; load centrally<\/td>\n<\/tr>\n \n Changed after tightening a bolt<\/td>\n Mechanics changed<\/td>\n Recalibrate<\/td>\n<\/tr>\n \n Reading saturates under load<\/td>\n Cell over its rating<\/td>\n Use a cell rated above your maximum<\/td>\n<\/tr>\n \n Noisy near a motor<\/td>\n Microvolt signals pick up interference<\/td>\n Separate the supplies; keep leads short<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Next steps<\/h2>\n
- \n
- Easier first:<\/strong> Digital and Analog, and When Each Applies<\/em>, for why an analog pin cannot do this.<\/li>\n
- Related products:<\/strong> a 16\u00d72 LCD to show the weight, and a push button for tare.<\/li>\n
- Next project:<\/strong> a kitchen scale with a display and a tare button, which is a genuinely useful object rather than a demonstration.<\/li>\n<\/ul>\n
Sources and attribution<\/h2>\n
All text, wiring guidance and code in this tutorial are original Siratek work.<\/p>\n
- \n
- HX711 datasheet for the 24-bit conversion, the sample rates and the channel arrangement.<\/li>\n
- The
E+ E- A- A+ B- B+<\/code> andGND DT SCK VCC<\/code> headers and the loose ten-pin header were read from the Siratek product photographs for item 2881. The same photographs show the board supplied without a load cell, which is why one appears in the parts list.<\/li>\n<\/ul>\nLoad cell wire colours are near-universal but not guaranteed, so the tutorial gives a test rather than asserting them. Offset and scale factor are presented as values the reader must measure, as they depend on the individual cell and its mounting. No third-party tutorial text, diagrams, photographs or code has been reproduced here.<\/p>\n
<\/p>\n<\/body>","protected":false},"excerpt":{"rendered":"
A load cell is a piece of metal that bends very slightly under weight, with strain gauges bonded to it that change resistance as it bends. The change is tiny: a few microvolts per gram.<\/p>\n","protected":false},"featured_media":0,"template":"","siratek_tutorial_level":[],"class_list":["post-52257","siratek_tutorial","type-siratek_tutorial","status-publish","hentry"],"yoast_head":"\n
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- Related products:<\/strong> a 16\u00d72 LCD to show the weight, and a push button for tare.<\/li>\n
- Load the other end through a platform<\/strong>, with spacers so the cell can bend. If the platform touches the base anywhere else, the force bypasses the cell and the reading goes nowhere.<\/li>\n
- A soldering iron. The supplied ten-pin header is loose and must be soldered on.<\/strong><\/li>\n