LG201: IoT Prototype Development - Electronic Circuits

Power Management

The 3-pin slide switch plays a major part in this circuit as it performs two tasks at the same time. The common pin is wired to the ESP32 Ground and the two circuit pins wired to the Shifter Ground and the Enable Pin on the ESP32, so one circuit is broken whilst the other is live.

Grounding the EN pin disables the 3.3v Regulator on the ESP32 whilst un-grounding the Shifter and breaking the 5v circuit driven by the Step-Up. Swapping it enables the 3.3v Regulator turning on the board, and grounds the 5v circuit. Without this double function, the Battery/USB power was still live on the 5v side of the board, the NeoPixels were pulling current even without a signal from the board.

The built-in power management is useful during development, as it means we can charge the battery whilst using the serial interface to programme the board, but as you’ve seen we have needed to add the Step-Up to achieve our 5v logic.

In final production where no Serial access is required, it would make more sense to deal with voltage and charging before powering the circuit, something along the lines of the functionality offered by the Adafruit Power-Boost breakout.

Security

In their article Modelling trust dynamics in the Internet of Things, Fernandez-Gago, Moyano & Lopez highlight one of the major obstacles facing IoT developers. As they state “It is expected that the ‘things’ involved in the IoT paradigm will have to interact with each other, often in uncertain conditions. It is therefore of paramount importance for the success of IoT that there are mechanisms in place that help overcome the lack of certainty. Trust can help achieve this goal.” [2] They go on to propose a Trust Management System that device manufacturers would sign up to.

Whilst this is beyond the scope of this module, there are interesting points raised that affect the hardware we should work with. I spent a year working on security for a system that would contain the most personal of data, I lost sleep over this whilst researching the answer.

The one weakness that struck me in all systems, was access to source code. If you could access and change the source code, then you could probably access data. With IoT devices, we literally give the customer the source code, if you can get the code of the Flash you can work out how any Key was created.

Articles like Data Security in Cloud Computing with Elliptic Curve Cryptography [3] explain the methodology and A secure inter-domain communication for IoT devices [4] highlight why the ESP32, with its built-in cryptography hardware, is a good contender for IoT development.

However, for me, the two most powerful features of the ESP32 are Flash Encryption [5] and Secure Boot. [6] These not only deny the owner access to the source code but effectively, once implemented, stop the device being written too again. There’s a simple explanation of these feature in Understanding ESP32’s- Security Features, [7] on Medium.

Once you have denied access to source code, you can have a truly Private key, though unless you have a production process that allows you to personalise the code on each board, there is still a risk that somebody knows how to generate it. It’s good to know I’m not the only person losing sleep over this. In an article about the new Digital Signature Peripheral in Series 2 of the ESP32, Amey Inamdar explains, “ESP32-S2’s Digital Signature Peripheral allows the manufacturer to generate the symmetric encryption key that can be unique to each device and then encrypt the device private key with the same encryption key.”" [8]

I’ll come back to Security in future modules, but we’re on the right track here.

1e Sensor Module

The idea of this device is that if I need it to perform different tasks, for example, record audio or measure movement, then the board remains the same and we just create a new breakout and a modified case.

Our current case has holes for the LED’ to shine through and a hole for the tactile switch, we don’t need to expose the sensor, it can live happily inside the case.

I already have ¼ Perma-Proto board screwed to the top of the case that houses the tactile switch, we’ll add another 4 terminal JST lead for the i2C connection and solder the sensor onto the board.

OK, we’re done wiring.