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Project Notes

#168 CurrentSensorModule

Test an ACS712 current sensor module with display on a 5110 LCD

The Build


This is a quick test of a current sensor module I picked up recently. It is rated for 5A (but other modules are available for different current scales).


The circuit simply measures a variable current (manually controlled wiper on a pot) and displays the result on a 5110 LCD. Minimum resistance of the load circuit is 10Ω, so +/-50V maximum input voltage to keep within the +/-5A tolerance of the module.

For test purposes with a 5V source and 0.25W resistors, I have R2 is set at 100Ω to prevent an overload. That means my test source only ranges from 0-50mA, so not a real power test.

In an alternative configuration, I have a 9V source pumping ~700mA through the current sensor.

At first my resultswere terrible, like+/-0.7A measuring as +/-0.2A. These readings are coincidentally quite consistent with a +/-20A scale. When I change to +/-20A sensitivity then suddenly my readings are very close to what my multimeter says.

Although the chip on my module is clearly marked ACS712ELC-05B (+/-5A sensitivity according to the datasheet), I’m guessing it is really an ACS712ELC-20A (+/-20A). Perhaps wrong markings in a QA reject batch? Perhaps also why it shows up in a 70 cent module from China!!

The Build 700mA

Module Specifications

  • the current sensor chips: ACS712ELC-05B
  • pin 5V power supply, on-board power indicator
  • the module can be measured plus or minus 5 amps, corresponding to the analog output of 185 mV / A
  • there is no the detection current through, the output voltage is VCC / 2

Given the +/-5A range and taking a reading through the analog point (0-1023), then the actual current will equal the analog input / 1023 * 2 * 5 - 5.

That’s a resolution of around 10mA, so not very sensitive, but perhaps good enough for gross current monitoring.

Module Connections

Pin/Terminal Description
+ Sensor power 3.3/5V
- Sensor ground
s Sensor output
VCC Input positive DC
GND Input ground

Module Construction

The module is basically connectors and a few supporting components around an ACS712 surface mount chip that does the hard work.

5110 LCD SPI Configuration

The u8glib takes advantage of hardware SPI, which means pin connections are dictated for at least MOSI and SCK.

Here’s the mapping from the terminology used by my particular 5110 module and pins on an Arduino Uno.

Pin Usage Arduino Uno Pin
RST reset 8
CE/SCE chip enable 10 SPI SS
DC address line 0 9
DIN data in 11 SPI MOSI
CLK clock 13 SPI SCK
VCC power  
BL Backlight on when GND  
GND Ground  



The Schematic

The Build

Credits and References

About LEAP#168 SensorsArduino
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.