This is a test and review of the new version of the FriedCircuits USB tester and backpack. If you read my previous articles on the backpack and its extensions, you already know that I am a big fan of this simple and very useful tool.

Before going further, one quick word in the interest of full disclosure: William kindly sent me the prototype for this backpack, and I actively contributed to influencing (in a good way I hope) the design of this new version.

So what is new ?

This review is actually about two separate items:

  • The FriedCircuits USB tester breakout v2.0
  • The FriedCircuits OLED backpack v2.0

Both have been improved in this new release, both on the firmware and the hardware sides, so let’s dive a bit deeper…

USB Tester v2.0

USB Breakout v1.4b

The USB tester is a really handy device that breaks out all signals on a – you guessed it – USB connection. It lets you measure both voltage and current and is really handy for debugging your own USB hardware if you do embedded development, or to qualify USB chargers (more on this below). The biggest change in v2.0 is that the input USB plug is now a micro USB. Pretty much all new devices sold today come with a micro USB connector – this is actually a European Standard – , so this is a really good bet for the future.

The layout has also been improved: new test points for multimeter leads, and not only banana plugs, and a larger space between the GND and VCC pins, so that it is not possible to accidentally place a jumper between those two. Another improvement that might not be immediately obvious at first, is that the banana plug holes are 0.75in spaced, which is a standard spacing for dual banana connectors. This is the kind of details that make a large difference in day to day usage!

So all in all,  lots of good incremental improvements! Note that if you paid close attention, you will notice the tester says “v1.4b”, is it actually the same as the final 2.0 version.

OLED Backpack v2.0

The largest changes are actually with the backpack: William decided to upgrade to a 128×64 OLED display (in place of the former 128×32), which gives us a lot more screen real estate, without requiring a larger PCB. By the way, both USB tester and OLED backpack follow the Dangerous Prototypes “Sick of Beige” form factor, which is really nice to work with as their proportions follow the Golden Ratio.

OLED Backpack v2.0

OLED Backpack v2.0

The new backpack also uses a micro USB connector, and its unique button has been relocated to the left side, which makes it easier to access.

The backpack works with both the USB breakout, and the generic current/voltage sensor breakout, as its predecessor. But in USB mode, you can now also measure the D+ and D- lines voltage. During an actual USB transfer, this will not be of much use, but it does not interfere either. On the other hand, when you use a USB charger, this features comes in very handy, since the voltage on D+ and D- lines actually often determines how fast the USB device is going to charge. This feature, as far as I know, is pretty unique on the market.

USB D+ / D- line measurement

This is one of the trickiest aspects of the device, actually. In a lot of scenarios, those voltages will be pretty much meaningless. But when used to qualify USB chargers, these will be sometimes useful, your mileage may vary there, and we would need more feedback from people using the backpack and the sort of values they are reading, in order to issue more recommendations on how to read those line voltages.

Serial interface

We did a lot of work on the serial interface for this version of the backpack. Most of the features are actually also supported on the previous backpack version. The main point is that the serial link is entirely managed through very simple serial commands and return values are embedded into JSON structures. This makes it super easy to interface with the backpack.

The firmware itself is written in an Arduino-friendly way, which means that the backpack behaves like an Arduino Leonardo board, and the firmware can be edited and loaded using the standard Arduino IDE. You can get the source code on Github, everything is fairly well documented and we strived at making it as easy to read as possible.

At the time of this writing (February 2014) , the following commands are supported: simple but effective. Don’t hesitate to suggest new commands or even better, contribute pull requests on Github!

  • R:XXXX : adjust serial output rate, XXXX is the rate in milliseconds. R:1000 will output a reading every second on the serial port.
  • S:X  : Switch to screen “X”. Numbering starts at “1”.
  • W:XXXX  : set current threshold to light up the blue LED. XXXX is in mA
  • Z:   : reset all counters (energy, etc). Do not forget the “:” after Z !

The backpack emits a JSON structure, as mentioned above, every few milliseconds, the delay is adjustable with the “R:” command. This structure contains pretty much every measurement variable of the backpack:

A word of explanation here: the “peak/min/avg” values for both the amps and volts measurements are the peak/min and averages values over the last measurement period. This means for instance, that if your serial output rate is 1000ms, then at each serial packet you will see how both current and voltage fluctuated within that measurement period. The internal measurement frequency of the OLED Backpack is 100ms, which is as fast or faster than most similar devices out there, so those min/max values are fairly accurate.

This is a very powerful feature once you grasp it: it means that even if you log with a relatively slow serial output rate, the device will always give you the boundaries of current and voltage fluctuations over each period. For a device that tends to do brief but large current peaks, you will not need to push up the serial output rate very much in order to get a good overview of the maximum current used. Pretty neat, eh ? See below for an example graph: on this graph, you can see the current consumption of a Nexus 7 graphed over a short period of time. The current actually fluctuates quite a bit, but thanks to this min/max/avg, you can see what the fluctuation range is, with very good accuracy:

Current on a Nexus 7

Current on a Nexus 7

Examples and Conclusion

If you read this far, you now realise that this apparently very simple device actually packs a lot of features under the hood! The serial interface, in particular, makes it an especially interesting testing instrument since it opens its possibilities a great deal!

One example below: this is a graph of the charging cycle of an Onyx geiger counter – from Kickstarter fame – , made by Medcom. I was debugging the charging circuit recently and needed to understand a bit better how the device charged. The app used to generate this is a custom web app that interfaces with the backpack directly, stay tuned to hear more on that front later this year!

Onyx charging cycle

Onyx charging cycle

As described above, you can see the use of the min/max/avg values on the two graphs, where you get a band where the values fluctuate. This is even better when using the current/voltage breakout board when you measure solar power.

William also offers a Java application that you can use to graph those values. This is the easiest way to get started on your computer. Below is a preview of the newest version of the application, check back on github for updates soon!

Java Data logger Beta 2

Java Data logger Beta 2

Another good use for this device, is that it lets you quickly check whether a USB charger actually does its job as it should. The two pictures below show my Nexus 5 being charged by two different USB chargers: pretty much day and night!

Good charger

Good charger

Bad charger

Bad charger

The same goes for car cigarette lighter adapters – took me a long time to find one that would actually charge at 2.1A as it claimed, most chargers on the market do not really work at that rate, of if they do, it is most often only with just a few devices (iPads in general), and others just fall back to 0.5A charging..

I hope this overview of the latest version of the OLED backpack and USB tester was useful to you. If that is the case, head over to Friedcircuits, you know what to do!

Leave a Reply

Your email address will not be published. Required fields are marked *