mirror of
https://github.com/RobTillaart/Arduino.git
synced 2024-10-03 18:09:02 -04:00
156 lines
6.4 KiB
Markdown
156 lines
6.4 KiB
Markdown
|
|
[](https://github.com/marketplace/actions/arduino_ci)
|
|
[](https://github.com/RobTillaart/ACS712/actions/workflows/arduino-lint.yml)
|
|
[](https://github.com/RobTillaart/ACS712/actions/workflows/jsoncheck.yml)
|
|
[](https://github.com/RobTillaart/ACS712/blob/master/LICENSE)
|
|
[](https://github.com/RobTillaart/ACS712/releases)
|
|
|
|
|
|
# ACS712
|
|
|
|
Library for the ACS712 Current Sensor - 5A, 20A, 30A.
|
|
|
|
|
|
## Description
|
|
|
|
The ACS712 is a chip to measure current, both AC or DC. The chip has an
|
|
analogue output that provides a voltage that is linear with the current.
|
|
The ACS712 library supports only a built in ADC by means of **analogRead()**.
|
|
There are 2 core functions:
|
|
|
|
- **int mA_DC()**
|
|
- **int mA_AC(float freq = 50)** The frequency can be set to typically 50 or 60 Hz
|
|
however other values e.g. 50.1 or 40 or 123.456 are possible.
|
|
|
|
To measure DC current a single **analogRead()** with conversion maths is sufficient to get
|
|
a value. To stabilize the signal **analogRead()** is called twice.
|
|
|
|
To measure AC current **a blocking loop for 20 milliseconds** is run to determine the
|
|
peak to peak value which is converted to the RMS value. To convert the peak2peak
|
|
value to RMS one need the so called crest or form factor. This factor depends heavily
|
|
on the signal form. For a perfect sinus the value is sqrt(2)/2 == 1/sqrt(2).
|
|
See Form factor below.
|
|
|
|
|
|
## Interface
|
|
|
|
#### Base
|
|
|
|
- **ACS712(uint8_t analogPin, float volts = 5.0, uint16_t maxADC = 1023, uint8_t mVperA = 100)** constructor.
|
|
It defaults a 20 A type sensor, which is defined by the default value of mVperA. See below.
|
|
- **int mA_AC(float freq = 50)** blocks ~21 ms (depending on the freq) to sample a whole 50 or 60 Hz period.
|
|
Since version 0.2.2 frequencies other integer values than 50 and 60 are supported, the lower the frequency,
|
|
the longer the blocking period.
|
|
Since version 0.2.3 floating point frequencies are supported to tune optimally.
|
|
- **int mA_DC()** blocks < 1 ms (Arduino UNO) as it just needs one **analogRead()**.
|
|
|
|
|
|
| type sensor | mVperA | LSB 5V-10bit |
|
|
|:-------------|:------:|:------------:|
|
|
| 5 A | 185 | ~25 mA |
|
|
| 20 A | 100 | ~50 mA |
|
|
| 30 A | 66 | ~75 mA |
|
|
|
|
|
|
#### Midpoint
|
|
|
|
- **void setMidPoint(uint16_t mp)** sets midpoint for the ADC conversion.
|
|
- **void autoMidPoint(float freq = 50)** Auto midPoint, assuming zero DC current or any AC current.
|
|
Note it will block for 2 periods. Since version 0.2.2 frequencies other than 50 and 60 are supported.
|
|
By setting the frequency to e.g 1, the code will sample for 2 seconds, possibly getting a better average.
|
|
- **uint16_t getMidPoint()** read the value set / determined.
|
|
- **void incMidPoint()** manual increase midpoint, e.g. useful to manually adjust the midPoint in an interactive application.
|
|
- **void decMidPoint()** manual decrease midpoint.
|
|
|
|
|
|
#### Form factor
|
|
|
|
Also known as crest factor; affects AC signals only.
|
|
|
|
- **void setFormFactor(float ff = ACS712_FF_SINUS)** manually sets form factor, must be between 0.0 and 1.0
|
|
- **float getFormFactor()** returns current form factor.
|
|
|
|
The library has a number of predefined form factors:
|
|
|
|
| definition | value | approx | notes |
|
|
|:---------------------|:--------------|:------:|:--------|
|
|
| ACS712_FF_SQUARE | 1.0 | 1.000 | |
|
|
| ACS712_FF_SINUS | 1.0 / sqrt(2) | 0.707 | default |
|
|
| ACS712_FF_TRIANGLE | 1.0 / sqrt(3) | 0.577 | |
|
|
| | | | |
|
|
|
|
It is important to measure the current with a calibrated multimeter
|
|
and determine / verify the form factor of the signal.
|
|
This can help to improve the quality of your measurements.
|
|
|
|
|
|
#### Noise
|
|
|
|
Default = 21 mV.
|
|
|
|
- **void setNoisemV(uint8_t noisemV = 21)** set noise level,
|
|
is used to determine zero level e.g. in AC measurements.
|
|
- **uint8_t getNoisemV()** returns the set value.
|
|
|
|
|
|
#### mV per Ampere
|
|
|
|
Both for AC and DC. Is defined in the constructor and depends on sensor used.
|
|
|
|
- **void setmVperAmp(uint8_t mva)** sets the milliVolt per Ampere measured.
|
|
- **uint8_t getmVperAmp()** returns the set value.
|
|
|
|
Typical values see constructor above.
|
|
|
|
|
|
#### Experimental
|
|
|
|
- **float detectFrequency(float minimalFrequency = 40)** Detect the frequency of the AC signal.
|
|
- **void setMicrosAdjust(float factor = 1.0)** adjusts the timing of micros in **detectFrequency()**.
|
|
Values are typical around 1.0 ± 1%
|
|
- **float getMicrosAdjust()** returns the set factor.
|
|
|
|
The minimum frequency of 40 Hz is used to sample enough time to find the minimum and maximum for 50 and 60 Hz signals.
|
|
Thereafter the signal is sampled 10 cycles to minimize the variation of the frequency.
|
|
|
|
The **microsAdjust()** is to adjust the timing of **micros()**.
|
|
It is only useful if one has a good source like a calibrated function generator to find the factor
|
|
to adjust. Testing with my UNO I got a factor 0.9986.
|
|
|
|
Current version is not performance optimized.
|
|
|
|
|
|
## Test
|
|
|
|
The library is tested with the RobotDyn ACS712 20 A breakout and an Arduino UNO.
|
|
|
|
|
|
## Operation
|
|
|
|
With the constructor the parameters **volts** and **maxADC (steps)** of the ADC are set
|
|
together with the **milliVolt per Ampere** value. The last parameter can be adjusted
|
|
afterwards, e.g. to calibrate this value runtime. Note this parameter affects both
|
|
AC and DC measurements.
|
|
|
|
To calibrate the zero level for DC measurements, 5 functions are available to
|
|
adjust the midPoint.
|
|
|
|
To calibrate the RMS value for AC measurements, 2 functions are available to
|
|
get and set the formFactor.
|
|
|
|
To calibrate the noise level (used for AC measurements), 2 functions are available to
|
|
get and set the noise in mV.
|
|
|
|
The examples show the basic working of the functions.
|
|
|
|
|
|
## Future
|
|
|
|
- mA_AC blocks 20 ms so might affect task scheduling on a ESP32.
|
|
This needs to be investigated. Probably need a separate thread that wakes up when new analogRead is available.
|
|
- **detectFrequency** also blocks pretty long.
|
|
- int point2point(float freq) function for AC. Is part of mA_AC() already.
|
|
Needs extra global variables, which are slower than local ones
|
|
Or just cache the last p2p value?
|
|
- external analogue read support? separate class?
|