Wiring up

Explore hardware setup examples for a variety of use cases.

Otii hardware features two main connectors and one expansion port. Multiple channels can be measured with the available inputs, such as main current, main power, main voltage, ADC current, ADC power, ADC voltage, SENSE+ voltage, SENSE- voltage, GPI1, and GPI2, as well as capturing serial logs from any embedded system or IoT devices.

To get the most out of the Otii Arc Pro and Otii Ace Pro, start by checking out the Expansion port to explore how to enhance measurement capabilities.

Power supply

Otii instruments are powered via USB cable from the computer. Both Otii Arc and Ace Pro can be powered by an external DC adapter. When using an external DC adapter, choose one from an established supplier.

The adapter should be low-noise, comply with IEC 60950-1 as a Limited Power Source, and have an output of 7 to 9 VDC for the Otii Arc Pro and 7 to 20 VDC for the Otii Ace Pro, with a maximum of 5 A.

Visit the FAQ Hardware page for more information on selecting the proper power supply.

Grounding (GND)

Otii Ace Pro is an isolated power supply. There are three isolation domains, the main channel (banana connectors), the expansion port and the USB/DC adaptor plug. When using the expansion port, there is a need to also connect AGND (Analog Ground) or DGND (Digital Ground) to DUT Ground. Otherwise, the expansion port will be floating.

Otii Arc Pro is not an isolated power supply, but we highly recommend to use a separate ground wire for the signal ground, attached to either DGND or AGND on the expansion port. This will prevent disturbances and measurement errors caused by voltage drops in the negative battery wire.

  • AGND is utilized as a reference point for analog measurements
  • DGND is used as a reference point for digital signaling

Internally Otii hardware, AGND and DGND are connected for both Otii Ace Pro and Otii Arc Pro

Measuring DUT

Power source and measure a Device Under Test (DUT).

Connecting DUT to Otii hardware

Set up Otii hardware, either the Otii Arc Pro or Otii Ace Pro, to work as a power source box providing constant voltage to the DUT, ranging from 0.5 V - 5 V / 0 V - 25 V, and enable it to measure output current and voltage.

Otii hardware setup

  1. Connect Otii hardware to your computer via USB. If needed, add a DC power supply via the DC plug.
  2. Connect Otii hardware’s banana connector positive lead to DUT positive (+) battery connector/power connector.
  3. Connect Otii hardware’s banana connector negative lead to DUT negative (-) battery connector/power connector (GND).
In case of connecting the DUT using the battery connector, remove the battery prior to connecting it to the Otii hardware.

Otii software setup

  1. Open the Otii 3 Desktop App, then select Create a new Otii Project
  2. In the left sidebar, find the CONTROL section. Within this section, add the Otii hardware identified by your computer. Just click the add button on the right side of the hardware identified.
  3. Considering the DUT's power ranges, set the required voltage for the added Otii hardware in the voltage box located on the left side of the power supply button.
  4. Under General Settings, make sure that the Power Box option is selected, and set an OC (overcurrent) protection for the DUT.
  5. Under Channels, select Main current to measure DUT's output current and Main voltage to measure DUT's output voltage. The Main power channel is assigned by default when the main current is selected to measure DUT's energy consumption.
  6. [Optional] The previously selected channels will be listed under the MEASUREMENTS section. In this section, the sampling rate, up to 50 ksps, can be set. (Only possible with the Otii Ace Pro)
  7. Click the record button in the upper left corner of the toolbar to start recording DUT measurements. Since your DUT is not powered on yet, only noise measurements will be observed at first.
  8. Turn on the DUT by clicking the power button next to the desired voltage assigned. Once turned on, the DTU measurements are being recorded.
  9. Now, it's time to validate, analyze, and optimize your embedded system or IoT devices.
Use wires with the lowest possible resistance and keep them as short as possible to minimize voltage drop, especially when the DUT consumes high current. The resistance in wires will be added to the total series resistance within the system, causing an unwanted voltage drop and an error in power and energy consumption measurements.
If the DUT consumes high current during power-up, causing high voltage drops in the attached wires, which directly affects the power-up cycle of the DUT since the voltage is too low. In case of experiencing this, connect one or several capacitors from Bat+ to Bat- on the DUT side to stabilize the voltage to start up the DUT properly. Note that the Otii Arc and Otii Ace have very low output capacitance for being a power source for the DUT but also a programmable load.

More use cases

More use cases, with instructions how to connect the hardware and set up the software can be found on the Use cases page.

Using expansion port ADC channel

The ADC+ and ADC- pins on the expansion port is both a single ended voltage measurement between ADC+ and AGND (ADC Voltage) and a differential voltage measurement between ADC+ and ADC- pins (ADC current). To use ADC current channel, an external sense resistor must be connected.

How to choose the resistor

For Otii Arc Pro

The differential input voltage range for the Otii Arc Pro ADC inputs goes from -81.9175 mV to 81.92 mV. Based on these values, the absolute maximum (peak) current through the sensing resistor must be determined.

Remember that by using Ohm's Law (V = I x R | I = V / R | R = V / I), the relationship between voltage, current, and resistance in an electrical circuit can be determined.

Here's an example to illustrate how to choose the resistor:

Suppose the system has a maximum peak current of 200 mA. By calculating, 0.08192 V / 0.2 A, the resistor value is equal to 0.41 ohms. But, the closest standard resistor value is 0.39 ohms. Resulting in a measuring range of 0.08192 V / 0.39 ohms = 0.210 A.

In conclusion, a 0.39 ohm sensing resistor will result in a measurement range of +/- 0.210 A.

For Otii Ace Pro

Following the same example as above, let's do the same for now but for the Otii Ace Pro.

The differential input voltage range for the Otii Ace Pro ADC inputs goes from -102.4 mV to 102.4 mV. Based on these values, the absolute maximum (peak) current through the sensing resistor must be determined.

Here's an example to illustrate how to choose the resistor:

Suppose the system has a maximum peak current of 200 mA. By calculating, 0.1024 V / 0.2 A, the resistor value is equal to 0.512 ohms. But, the closest standard resistor value is 0.51 ohms. Resulting in a measuring range of 0.1024 V / 0.51 ohms = 0.200 A.

In conclusion, a 0.51 ohm sensing resistor will result in a measurement range of +/- 0.200 A.