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139 lines
4.2 KiB
Markdown
139 lines
4.2 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/MAX471_RT/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/MAX471_RT/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/MAX471_RT/issues)
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[](https://github.com/RobTillaart/MAX471_RT/blob/master/LICENSE)
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[](https://github.com/RobTillaart/MAX471_RT/releases)
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[](https://registry.platformio.org/libraries/robtillaart/MAX471)
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# MAX471
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Arduino library for MAX471 current sensor.
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## Description
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The MAX471 is an older current sensor which can handle up to 50 Watt,
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with a maximum of 25 Volts or a current of 3 Amperes.
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It is officially not supported anymore however there are still many
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for sale.
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The MAX471 is also in the market as the GY-471.
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The MAX472 seems to be compatible with this library but it uses
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has some different wiring. Details see datasheet.
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The library is **experimental** and needs testing.
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Feedback, issues and improvements are welcome,
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Please open an issue on GitHub.
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#### Limits
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**Warning** Use a voltage divider if you measure voltages above the
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range that is supported by your processor!
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Always include some safety margin (10%) in such voltage divider so
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the peak is about 90% of the ADC range.
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| unit | limits | notes |
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|:---------:|:----------:|:----------|
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| Power | 50 Watt | total
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| Voltage | 25 Volt | at 2 A
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| Current | 3 Ampere | at 16 V
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#### Related
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- https://wolles-elektronikkiste.de/en/max471-current-sensor (excellent explanation)
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## Connection
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There are two breakout board variants, a purple board and a red board.
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The main difference is that the purple board has a sign pin.
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This pin indicate the direction of the current.
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The library has two constructors, one with and one without the signPin parameter.
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## Interface
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```cpp
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#include "MAX471.h"
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```
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#### Constructor
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The MAX471 needs two ADC pins. Current version does not support sharing
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the same pin for both current and voltage.
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An external multiplexer could handle this.
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- **MAX471(uint8_t currentPin, uint8_t voltagePin)** red + purple board
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- **MAX471(uint8_t currentPin, uint8_t voltagePin, uint8_t signPin)** purple board.
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#### Configure
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- **void begin(float maxVoltage = 5, uint16_t maxSteps = 1023)**
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Sets the parameters voltage and maxSteps of the internal ADC.
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Note this allows to update the voltage runtime.
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Steps must be larger than zero of course, typical 255 (8 bit), 1023 (10 bit),
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4095 (12 bit).
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**begin()** can be called multiple times to adjust e.g. the voltage used.
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Think of setting the analog reference (AREF) to 1V1.
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#### Read
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- **float readCurrent(uint8_t times = 1)** returns Ampere
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- **float readCurrentMA(uint8_t times = 1)** wrapper, returns milliAmpere
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- **float readVoltage(uint8_t times = 1)** returns Volts
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- **float calcPower()** returns Watt, but only after current and voltage
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has been read as it uses the cached values.
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## Future
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#### Must
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- improve documentation
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- buy hardware MAX471
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- test with hardware
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#### Should
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- examples
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- integrate current over time.
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- performance
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- AREF for UNO?
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#### Could
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- support shutDown pin. LOW/GND = ON, HIGH = OFF.
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- not on breakout boards.
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- investigate AREF 1V1 to improve resolution.
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- multiplex the ADC
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- external ADC (ADS1115) for higher resolution.
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#### Ideas
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- add derivative of current + voltage (raising falling indicator)
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- percentage interface
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- warning limits reached.
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#### Won't
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## Support
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If you appreciate my libraries, you can support the development and maintenance.
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Improve the quality of the libraries by providing issues and Pull Requests, or
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donate through PayPal or GitHub sponsors.
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Thank you,
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