October 2023 Newsletter

Here in Maryland, USA, fall is upon us with falling temperatures and falling leaves. Passing time brings both a new season and new Joulescope features!

In this issue, we’ll cover:

Visit us at the PCB Carolina Trade Show
Circuit Cellar JS220 Review
Sneak Peek: Software-controlled Fuse Feature
US Patent Grant

PCB Carolina Trade Show

If you live in the Research Triangle Park area near Raleigh, North Carolina, USA, consider attending PCB Carolina on November 8, 2023. We will be exhibiting! Stop by table #32 and chat with Matt Liberty, the creator of Joulescope.

PCB Carolina includes 16 technical sessions, a keynote address, a vendor exhibition with over 70 companies participating, and food. Attending the conference is FREE, and you get breakfast, lunch, and an evening reception!

Visit the PCB Carolina website for more details and to sign up.

Brian Millier wrote an in-depth Joulescope JS220 review for the April 2023 Circuit Cellar edition. Just before writing this article, Brian had designed his own MCU-based IoT Power monitor, so he was already very familiar with the challenge of accurately measuring active and sleep currents. This expertise clearly shows as he explores the JS220’s capabilities. Unfortunately, we went and launched the Joulescope UI 1.0 only two months later, and all of the article images still use UI 0.10.

Circuit Cellar has kindly published this article free of charge.

In case you missed it, you can check out these other past Joulescope JS220 teardowns and reviews:

Sneak Peek: Software-controlled Fuse

The Joulescope UI 1.0 launched in June introduced many improvements and long-standing feature requests. UI 1.0 also brings the capability to customize behaviors for the JS110, JS220, and future products. The first new JS220-specific feature will be a software-controlled fuse.

The Joulescope JS220 can fully and bidirectionally disconnect the Current + from Current -. You can already do this manually by clicking the Target power button. However, we want a more automated way to protect the JS220 and your target devices.

The software-controlled fuse feature will have four channels: two user-configurable channels for target protection and two fixed channels for JS220 protection. For the two user channels, you will be able to set a current threshold. When the current exceeds this threshold, the fuse will eventually trip. You can also control how quickly the fuse trips by specifying a second current threshold and a duration. If you provide a constant current at this second threshold, the fuse will trip in that duration. These parameters will enable you to control fuse responsiveness easily.

Here is the same 1 A current first threshold with a 50 ms trip time at different second thresholds:

JS220’s will include this always-enabled fuse channel to protect themselves:

Although this design is all digital, it mimics real-world fuses that trip based on heat. The digital fuse accumulates heat and dissipates heat. If it passes a threshold “temperature,” the fuse trips.

Heat is power, so this design operates on current squared with a heating and cooling coefficient. The discrete time equation to determine the energy accumulation a per sample i is:

The fuse then trips when a exceeds a defined threshold T, corresponding to the heating coefficient.

Solving this first-order ordinary differential equation allows direct computation of K and T from our trip duration and two current thresholds. With some fixed point math, the JS220’s FPGA efficiently runs this fuse algorithm in real-time.

We have already completed the instrument component of this feature. The remaining step is to add UI configuration and control, which we have started.

This completed feature will be coming to all Joulescope JS220’s through a UI update soon!

US Patent Grant

We proudly announce that the US Patent Office granted patent 11,774,469 entitled “Auto Ranging Ammeter with Accurate Measurement during Range Changes”. This patent describes the invention that enables the Joulescope JS220’s excellent dynamic performance.

Combined with our US Patent 11,249,117, we continue leading the industry in affordable, accurate, high-dynamic range current measurement!

Curious about whether a Joulescope is the perfect fit for your needs or have questions about its functionalities? We're here to help! Reply to this email, contact us directly, or join the conversation on the Joulescope forum!