The Otii Arc from QOITECH is an excellent product for analyzing and optimizing power consumption in IoT devices. It is a programmable power supply and measurement unit with companion analysis software. The power supply provides a maximum output voltage of 5 V and current measurement range of 1 μA - 5 A. Additionally it features an ADC channel that can be used to measure subsystem current and a UART for logging serial data. Information on using the Otii Arc and software download is on Qoitech’s website https://www.qoitech.com/ .
This post describes using the Otii Arc with a modified Digi International XBIB-U-DEV development board to measure supply current and log serial data of an Xbee radio plugged into the board. The Otii Arc’s subsystem ADC and UART are connected to the current sense resistor and UART of the XBIB-U-DEV. Modifications were made to the XBIB-U-DEV to replace the shunt resistor with a current sense resistor and add male header pins to simplify wiring to the Otii Arc. Once modified, any compatible Xbee radio can be plugged into the development board for testing.
Note: modifying the XBIB-U-DEV voids the warranty
Board modifications made are described below and highlighted in circled red areas of the XBIB-U-DEV Reference Guide:
- Remove R31 (0 ohm jumper) and replace with a current sense resistor of value 0.075 ohms
- Add male header pins to P1, P6 and J5
Wiring connections between the Otii Arc and XBIB-U-DEV are listed and shown below:
- Otii - RX connected to P1 - position 2 (DOUT)
- Otii - AGND connected to P1 - position 10 (GND)
- Otii - ADC+ connected to P6 - square pad (R31)
- Otii - ADC- connected to P6 - round pad (R31)
- Otii - DGND connected to J5 - square pad (GND)
Below screen shot of the Otii software tool shows example current, voltage and UART data from a XBC-V1-UT-001 cellular modem. As shown in gray, users can select time ranges of the graphed data which displays min, max, average current/voltage measurements and energy consumption for the highlighted region.
