Joulescope JS220 uUSB Front Panel

The uUSB FP is a versatile panel for the Joulescope JS220 power analyser that enables power measurement of any USB device.

Key Features

• Multiple USB connector types supported:
  • USB Type-C
  • USB Type-A
  • Micro USB
  • Screw terminals for custom connections
• Supports any combination of input terminal and output terminal
• Compatible with Joulescope JS220
• Supports USB 2.0 High Speed (HS) data pass-through with minor performance impact

Setup Instructions

Host Connection (Input Side)

1. Choose any of the available input connectors:
   • USB Type-C port
   • USB Type-A port
   • USB Micro-B port
   • Screw terminals
2. Connect your host device (e.g., laptop, power supply)

Device Connection (Output Side)

1. Choose any of the available output connectors:
   • USB Type-C port
   • USB Type-B port
   • USB Micro-AB port
   • Screw terminals
2. Connect your device under test
3. Power up your Joulescope JS220

Important Notes

⚠️ USB Type-C Connection. Due to USB Type-C specification limitations:

• If power isn't flowing, flip the connector orientation at one end of one of the USB Type-C cables.
• This is a normal behaviour for pass-through devices when used with compliant USB Type-C cables

Best Practices

• Always verify connections before powering on
• The compact screw terminals are compatible with PH000 screwdrivers
• When using screw terminals, ensure proper polarity
• Monitor power readings through the Joulescope software interface
• Keep connections secure during measurements

Data Performance

The panel routes the data lines through all the connectors to provide maximum connectivity flexibility. This is inherently going to impact signal integrity.

In order to measure the impact, I connected a USB 3 capable drive with a USB 2.0 extension cable to make USB the bottleneck, not the drive. This was the baseline reading.

For the uUSB FP reading, the USB drive was connected to the panel, then the panel was connected to the laptop (host) with the USB-B port.

Using the USB test script, the following graphs were produced. The script ran 30 tests of 512MB transfers.

Read

The average read speed was only 0.4 MB/s slower than baseline, but with more consistent speeds. This is likely noise from the tests.

Write

The average write speed is very similar to the baseline, however there is greater fluctuation.

Summary

The read and write speeds achieved without the uUSB FP, while lower than the USB 2.0 HS theoretical maximum of 60MB/s, are typical data rates in practice. Introducing the uUSB FP shows only a small reduction in maximum speed, although there appears to be more fluctuation. Given the signal integrity reduction inherent in a passive pass-through device, this is not unexpected. The overall speed achieved is a function of the protocol, the cables, the uUSB FP, the host computer and the USB drive itself, so individual results may vary.

Test conditions

The white USB cable with the USB drive attached is the baseline test, and the uUSB test would have the USB drive plugged into the Joulescope.

The script used for testing can be found here. Note the script is built for Linux and it might run Mac OS, but changes will have to be made in order to use it on Windows.

Schematic

The schematic is located on the GitHub repository.