fix #54, calibration sketch (#55)

- fix #54, calibration sketch should output int32_t for offset. - update examples - update readme.md - minor edits
RobTillaart · Nov 8, 2024 · 8dd2657 · 8dd2657
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diff --git a/CHANGELOG..md b/CHANGELOG..md
@@ -5,6 +5,12 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.5.1] - 2024-11-08
+- fix #54, calibration sketch should output int32_t for offset.
+- update examples
+- update readme.md
+- minor edits
+
 ## [0.5.0] - 2024-06-17
 - fix #50, bug in constructor (thanks Mathieu!)
   - refactor constructor

diff --git a/HX711.cpp b/HX711.cpp
@@ -1,7 +1,7 @@
 //
 //    FILE: HX711.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.5.0
+// VERSION: 0.5.1
 // PURPOSE: Library for load cells for UNO
 //     URL: https://github.com/RobTillaart/HX711_MP
 //     URL: https://github.com/RobTillaart/HX711
@@ -108,7 +108,7 @@ float HX711::read()
 
   union
   {
-    long value = 0;
+    int32_t value = 0;
     uint8_t data[4];
   } v;
 
@@ -375,13 +375,13 @@ float HX711::get_scale()
 }
 
 
-void HX711::set_offset(long offset)
+void HX711::set_offset(int32_t offset)
 {
   _offset = offset;
 }
 
 
-long HX711::get_offset()
+int32_t HX711::get_offset()
 {
   return _offset;
 }

diff --git a/HX711.h b/HX711.h
@@ -2,7 +2,7 @@
 //
 //    FILE: HX711.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.5.0
+// VERSION: 0.5.1
 // PURPOSE: Library for load cells for Arduino
 //     URL: https://github.com/RobTillaart/HX711_MP
 //     URL: https://github.com/RobTillaart/HX711
@@ -15,7 +15,7 @@
 
 #include "Arduino.h"
 
-#define HX711_LIB_VERSION               (F("0.5.0"))
+#define HX711_LIB_VERSION               (F("0.5.1"))
 
 
 const uint8_t HX711_AVERAGE_MODE = 0x00;
@@ -143,8 +143,8 @@ class HX711
   float    get_scale();
 
   //  OFFSET > 0
-  void     set_offset(long offset = 0);
-  long     get_offset();
+  void     set_offset(int32_t offset = 0);
+  int32_t  get_offset();
 
   //  clear the scale
   //  call tare() to set the zero offset
@@ -177,7 +177,7 @@ class HX711
   uint8_t  _clockPin;
 
   uint8_t  _gain;
-  long     _offset;
+  int32_t  _offset;
   float    _scale;
   uint32_t _lastRead;
   float    _price;

diff --git a/README.md b/README.md
@@ -29,7 +29,7 @@ This translates roughly to 4 or max 5 significant digits in a single measurement
 That's why multiple measurements are advised to average and reduce the noise.
 
 
-#### Breaking change 0.3.0
+### Breaking change 0.3.0
 
 In issue #11 it became clear that the timing of the default **shiftIn()** function to 
 read the value of the internal ADC was too fast on some processor boards for the HX711.
@@ -44,7 +44,7 @@ Drawback is that reading the HX711 takes an extra 50-55 microseconds.
 How much this affects performance is to be investigated.
 
 
-#### HX711_MP
+### HX711_MP
 
 - https://github.com/RobTillaart/HX711_MP
 
@@ -61,7 +61,7 @@ This multi-point calibration allows to compensate for non-linear behaviour
 in the sensor readings.
 
 
-#### 10 or 80 SPS
+### 10 or 80 SPS
 
 The datasheet mentions that the HX711 can run at 80 samples per second SPS. 
 To select this mode connect the **RATE** pin(15) of the chip to VCC (HIGH).
@@ -75,12 +75,17 @@ If there is a need (issue) I will implement this in the library.
 For now one can add an IOpin for this and use **digitalWrite()**.
 
 
-#### Related
+### Related
 
 - https://github.com/bogde/HX711
 - https://github.com/RobTillaart/weight  (conversions kg <> stone etc.)
 - https://github.com/RobTillaart/HX711
-- https://github.com/RobTillaart/HX711_MP
+- https://github.com/RobTillaart/HX711_MP  multipoint calibration version.
+
+
+### Faulty boards
+
+- https://forum.arduino.cc/t/load-cell-amplifier-hx711-wrong-ground/1046075
 
 
 ## Main flow
@@ -107,14 +112,18 @@ Steps to take for calibration
 #include "HX711.h"
 ```
 
-#### Base
+### Constructor
 
 - **HX711()** constructor.
 - **~HX711()**
 - **void begin(uint8_t dataPin, uint8_t clockPin, bool fastProcessor)** sets a fixed gain 128 for now.
 The fastProcessor option adds a 1 uS delay for each clock half-cycle to keep the time greater than 200 nS.
 - **void reset()** set internal state to start condition.
 Since 0.3.4 reset also does a power down / up cycle.
+
+
+### Read
+
 - **bool is_ready()** checks if load cell is ready to read.
 - **void wait_ready(uint32_t ms = 0)** wait until ready, check every ms.
 - **bool wait_ready_retry(uint8_t retries = 3, uint32_t ms = 0)** wait max retries.
@@ -130,7 +139,7 @@ The weight alpha can be set to any value between 0 and 1, times >= 1.
 - **uint32_t last_read()** returns timestamp in milliseconds of last read.
 
 
-#### Gain + channel
+### Gain + channel
 
 Use with care as it is not 100% reliable - see issue #27. (solutions welcome).
 
@@ -169,13 +178,13 @@ as the datasheet states it should be. So use with care. (feedback welcome)
 See discussion #27. 
 
 
-#### Mode 
+### Read mode
 
 Get and set the operational mode for **get_value()** and indirect **get_units()**.
 
 Constants (see .h file)
 
-- **HX711_RAW_MODE** new in 0.3.3 
+- **HX711_RAW_MODE**
 - **HX711_AVERAGE_MODE**
 - **HX711_MEDIAN_MODE**
 - **HX711_MEDAVG_MODE**
@@ -193,7 +202,7 @@ to keep memory footprint relative low.
 - **uint8_t get_mode()** returns current set mode. Default is **HX711_AVERAGE_MODE**.
 
 
-#### Get values
+### Get values
 
 Get values from the HX711 corrected for offset and scale.
 Note that in **HX711_RAW_MODE** the times parameter will be ignored => just call **read()** once.
@@ -203,11 +212,11 @@ Note that in **HX711_RAW_MODE** the times parameter will be ignored => just call
 - **bool set_scale(float scale = 1.0)** set scale factor which is normally a positive number larger than 50. Depends on load-cell used.
 Returns false if scale == 0.
 - **float get_scale()** returns set scale factor.
-- **void set_offset(long offset = 0)** idem.
-- **long get_offset()** idem.
+- **void set_offset(int32_t offset = 0)** idem.
+- **int32_t get_offset()** idem.
 
 
-#### Tare & calibration I
+### Tare & calibration I
 
 Steps to take for calibration
 1. clear the scale.
@@ -227,7 +236,7 @@ Assumes offset is not zero, which is true for all load cells tested.
 - **void calibrate_scale(uint16_t weight, uint8_t times = 10)** idem.
 
 
-#### Tare & calibration II
+### Tare & calibration II
 
 A load cell + HX711 module without weight gives a raw value, mostly not equal to zero.
 The function **get_tare()** is used to measure this raw value and allows the user
@@ -248,7 +257,7 @@ Furthermore it is also important to do the calibration at the temperature you
 expect to do the weight measurements. See temperature section below.
 
 
-#### Inner formula
+### Inner formula
 
 Weight = **get_scale()** x raw + **get_tare()**.
 
@@ -258,7 +267,7 @@ This can be compared with actual values to get an indication
 of the accuracy of the load cell.
 
 
-#### Power management
+### Power management
 
 - **void power_down()** idem. Explicitly blocks for 64 microseconds. 
 (See Page 5 datasheet). 
@@ -267,7 +276,7 @@ It should reset the HX711 to defaults but this is not always seen.
 See discussion issue #27 GitHub. Needs more testing.
 
 
-#### Pricing
+### Pricing
 
 Some price functions were added to make it easy to use this library
 for pricing goods or for educational purposes. 
@@ -279,10 +288,31 @@ For weight conversion functions see https://github.com/RobTillaart/weight
 - **float get_unit_price()** idem.
 
 
+### Millivolts
+
+**Experimental**
+
+To be verified in a test setup.
+
+In issue #53, a question was asked to convert the input of the HX711 to milivolts.
+Thinking about this question resulted in a simple and imho an elegant idea:
+
+- Apply 0.000 mV to the system.
+- Call **tare(times)** to calibrate the zero point. 
+- Then apply 20.000 mV to the system.
+- Call **calibrate_scale(20000)** to map the raw reading to 20000 µV = 20 mV.
+
+Assuming the scale is linear, the HX711 now works like a millivolt meter.
+And the **float get_units(uint8_t times = 1)** will return microvolts.
+
+In fact, one could map any linear unit this way, e.g. if the voltage applied 
+is linear with temperature, humidity or windspeed one can map this directly.
+
+
 ## Notes
 
 
-#### Scale values for load cells
+### Scale values for load cells
 
 These scale values worked pretty well with a set of load cells I have, 
 Use calibrate to find your favourite values.
@@ -291,7 +321,7 @@ Use calibrate to find your favourite values.
 - 20 KG load cell  scale.set_scale(127.15);
 
 
-#### Connections HX711
+### Connections HX711
 
 - A+/A-  uses gain of 128 or 64
 - B+/B-  uses gain of 32
@@ -308,7 +338,7 @@ Colour scheme wires of two devices.
 |      B+     |  not connected  |  not connected  |
 
 
-#### Temperature
+### Temperature
 
 Load cells do have a temperature related error. (see datasheet load cell)
 This can be reduced by doing the calibration and take the tare
@@ -322,20 +352,20 @@ differences in your code.
 ## Multiple HX711
 
 
-#### Separate lines
+### Separate lines
 
 Simplest way to control multiple HX711's is to have a separate **DOUT** and **CLK** 
 line for every HX711 connected.
 
 
-#### Multiplexer
+### Multiplexer
 
 Alternative one could use a multiplexer like the https://github.com/RobTillaart/HC4052
 or possibly an https://github.com/RobTillaart/TCA9548.
 Although to control the multiplexer one need some extra lines and code.
 
 
-#### Share CLOCK line
+### Share CLOCK line
 
 See **HX_loadcell_array.ino**
 
@@ -368,7 +398,6 @@ See https://github.com/RobTillaart/HX711/issues/40
 - update documentation HX711
 - keep in sync with HX711_MP
 
-
 #### Should
 
 - test B channel explicitly.
@@ -377,7 +406,6 @@ See https://github.com/RobTillaart/HX711/issues/40
   - investigate the need of yield after interrupts
   - investigate blocking loop at begin => less yield() calls ?
 
-
 #### Could
 
 - test different load cells
@@ -389,7 +417,6 @@ See https://github.com/RobTillaart/HX711/issues/40
 - add **setRate()** and **getRate()** - sample rate 10/80 SPS
   - optional?
 
-
 #### Wont
 
 - why store the gain as \_gain while the iterations m = 1..3 is used most

diff --git a/examples/HX_calibration/HX_calibration.ino b/examples/HX_calibration/HX_calibration.ino
@@ -1,26 +1,24 @@
 //
 //    FILE: HX_calibration.ino
 //  AUTHOR: Rob Tillaart
-// PURPOSE: HX711 demo
+// PURPOSE: HX711 calibration finder for offset and scale
 //     URL: https://github.com/RobTillaart/HX711
 
 
 #include "HX711.h"
 
 HX711 myScale;
 
+//  adjust pins if needed.
 uint8_t dataPin = 6;
 uint8_t clockPin = 7;
 
-uint32_t start, stop;
-volatile float f;
-
 
 void setup()
 {
   Serial.begin(115200);
   Serial.println(__FILE__);
-  Serial.print("LIBRARY VERSION: ");
+  Serial.print("HX711_LIB_VERSION: ");
   Serial.println(HX711_LIB_VERSION);
   Serial.println();
 
@@ -45,8 +43,9 @@ void calibrate()
   while (Serial.available() == 0);
 
   Serial.println("Determine zero weight offset");
-  myScale.tare(20);  // average 20 measurements.
-  uint32_t offset = myScale.get_offset();
+  //  average 20 measurements.
+  myScale.tare(20);
+  int32_t offset = myScale.get_offset();
 
   Serial.print("OFFSET: ");
   Serial.println(offset);