June Birth Magoncia

user Electronics Engineer

city Innovuze Solutions, Inc.

  • 4.5 Digit BLE Enabled IoT Wireless Digital Multimeter

  • Created: Apr 18, 2017

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The Internet of Things (IoT) environment connects different devices nowadays. These devices are embedded with microcontrollers, sensors, actuators, transceivers, etc. that allow the devices to collect and exchange information. In this reference design, a 4.5 digit Bluetooth low energy (BLE) enabled IoT wireless digital multimeter (DMM) is featured. This DMM is based on Texas Instruments CC2640F128RGZR device which is an ultra low-power wireless microcontroller that is optimized for BLE applications.

As shown in the circuit, the design is made up of many subsystems. The CC2640F128RGZR wireless microcontroller handles system control, BLE communication, and data processing. For voltage and current measurements, an analog front end (AFE) circuitry is used for signal conditioning. This sub-circuit is composed of TS5A3359DCUR, TS3A24159DRCR, TS5A3166DCKR, GS-113-0043, OPA2313IDRGR, THS4531IDGK, and some passive components. The conditioned signal from the AFE is converted into digital by the ADS8885IDRCR ADC and the ADC sends the data to the CC2640F128RGZR microcontroller after the conversion. The REF3325AIDCKTG4 is used for ADC reference and the OPA313IDCKR buffers the reference voltage, while the OPA333AIDCKR is used for common mode offset. In BLE devices, pairing usually requires some type of interaction with the user to confirm the identity of the user or the device being paired. So in order to simplify the pairing process and make it easier for the user to go through a one-step pairing process, the design includes automatic BLE pairing enabled by the RF430CL330HIRGTR dynamic Near-field communication (NFC) interface transponder. In addition, this NFC pairing solution features battery-less operation, whereby the energy required by this subsystem is harvested from the radiated field that enables the communication with the pairing device. The design also implements a wake-up feature using CapTIvate handled by the MSP430FR2532IRGER microcontroller. This helps in saving battery life because if the DMM is not being used to take measurements, some system components are disabled to save energy. The MSP430FR2532IRGER microcontroller allows for ultra-low-power consumption while actively monitoring for any device-handling condition. If detected while in the power-down state, the CapTIvate feature forces all devices back into the active mode. The design operates from a 3.7V lithium-ion battery. The 3.7V is regulated into different voltages (1.9V, 2.7V, 2.8V, and 3V) to supply the different devices used in the circuit. The BQ27426YZFR monitors the voltage and the stage-of-charge of the lithium-ion battery source. The status of the battery is sent by the BQ27426YZFR to the CC2640F128RGZR though a serial interface. The battery can be also charged through the micro-USB port which is connected to the BQ24232RGTR device that charges the battery.

This DMM can be used for basic DC voltage and current measurement modes as well as true RMS AC voltage and current measurement. It has four voltage ranges (50V, 5V, 500mV, and 50mV) and two current ranges (50mA and 500µA). For voltage measurement, the DMM can display 50,000 display counts with a resolution of 1µV, 10µV, 100µV, and 1mV for 50mV, 500mV, 5V, and 50V input ranges, respectively. In measuring current, it can also display 50,000 display counts with a resolution of 10nA for 500µA input range and 1µA for 50mA input range. The DC measurement accuracy is 0.10%, while for AC is 3% for frequencies up to 100kHz. For a battery with 600mAh capacity, the DMM can operate continuously for at least 100 hours. The reading of the DMM can be displayed to a smartphone or tablets through a mobile app or through a PC LabVIEW environment using a BLE USB dongle with a proprietary serial port communication API.