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Introduction

This project details a proof of concept implementation of a 100 Amp Bluetooth wireless current sensor. Riedon's SSA-100 current sensor provides an isolated analog voltage signal that is ratiometric (12mV/Amp) of the current passing though it's busbar terminals. A CircuitPython program running on Adafruit's Feather nRF52840 Express board controls an Adafruit 1085 break out board (based on Analog Devices ADS1115 16 bit ADC) to measure the Riedon sensor's current signal and sends the measurements over Bluetooth to a Pixel 3a Android phone. The phone runs Adafruit's Bluefruit LE Connect Android app to display the current measurements sent by the nRF52840 Express. 

Hardware Requirements


Supplier Documentation

Test Setup

Hardware Setup

The Feather nRF52840 Express board is powered by a 5V USB power supply and it provides 3.3V to the ADS1115 board and SSA-100 sensor and interfaces with the ADS1115 over I2C. The ADS1115 differential inputs A0 and A1 are connected to the differential outputs +Vo and -V0 of the SSA-100. A JST 04R-JWPF-VSLE-S connector fitted with pre-crimpled leadwires is plugged into the SSA-100 to provide external connections to power, ground, +Vo, and -Vo. For testing the SSA-100 was mounted in an SSA-BASE and the busbar terminals connected in series with the+12V battery terminal and main power cable of a Honda ATV. The test load is the power winch on a Honda ATV and current through the SSA-100 is measured when engaging the winch in pull and reverse modes.



Bluetooth Setup

Adafruit's Bluefruit LE Connect Android app was installed on a Google Pixel 3a Android phone and used to display the current measurements sent by the nRF52840 Feather Express board. Both the UART and Plotter modes of the BlueFruit LE Connect app can be used to display current measurements sent by the Feather Express.



Test Results

Test results showed peak currents approaching 80 amps when engaging the ATV's power winch. Nominal winch current was approximately 25 amps when pulling and 18 amps in reverse.




Test Electrical Connections and Wiring Diagram


Full Scheme-it project including BOM is at link https://www.digikey.com/schemeit/project/riedonssa-circuit-55d2f6e0a8844c1eb96dca10a5603635

Example Code

CircuitPython example code runs on the nRF52840 Feather Express to set up a Bluetooth connection and command the ADS1115 board to take differential measurements of the SSA-100 differential analog output voltage current signal. Once a Bluetooth connection is established with an Android phone running the Bluefruit LE Connect app, the nRF52840 Feather Express continuously runs the main program loop sending current measurements over Bluetooth to the Android phone and debug data to the CircuitPython serial connection. Two versions of example code were developed. Riedon_BLE_Plotter.py works with the Bluefruit LE Connect app's Plotter mode to display the current measurements graphically. Riedon_BLE_UART.py works with the Bluefruit LE Connect app's UART mode to display current measurements as ASCII text in a terminal window. Latest version example code is on github at Riedon_BLE_UARTrev1.py and Riedon_BLE_plotter_rev1.py .




Riedon SSA Current Sensor Details


Riedon’s SSA Smart Current Sensors integrate a high-power low resistance shunt with an isolated precision amplifier and the offers models with current measurement ranges from 100A to 1000A. Key features include 1500VDC reinforced isolation, 0.1% accuracy, ± 0.1% linearity over current range, unipolar power supply, differential analog output and 300kHz bandwidth. 


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