System Design: An initial dive in

A project log for PR-Holonet: Disaster Area Emergency Comms

An easy to build, setup, and use emergency communicator for disaster-struck zones with no working power or comms infrastructure.

inventive.prototypesinventive.prototypes 04/18/2018 at 04:060 Comments

Hardware Communication Gateway

PR-Holonet consists of 2 parts:

Both systems are meant to be as low cost and modular as possible. The full hardware communications unit is composed of :

Raspberry Pi 3 and Rockblock MK II

36W 18V solar charger

You get 2 USB 2.0 charging ports (5V/2.4A) and one 18V/1.5A barrel port

40Ah Lithium battery. Can power a laptop. Also has a simple but useful LED "flashlight"

Nice waterproof box large enough for everything

At its most basic setup, PR-Holonet is composed of the Raspberry Pi 3 and the Rockblock. The Pi runs a Flask web server that serves as the interface for the user. It is also responsible for generating the WiFi access point that users will connect to. The Pi is used to power the Rockblock MK II, which is responsible for beaming the messages up to the Iridium satellite constellation. The Rockblock talks to the Pi over serial and can be connected by hand to the Pi.

Connecting the Rockblock

Connecting the Pi

On a 26.8AH lithium battery, PR-Holonet can be on for a couple days (3 to 4 so far in my experience, although I have yet to do a well-documented test). Depending on needs, you can find upwards of 50Ah batteries which can also be used to power and recharge a full laptop. In my current iteration I am using a 40 Ah battery. When coupled together with a foldable solar charger, the system can effectively be on 24/7. What’s more, given that PR-Holonet consumes little power, the system can generate enough power for itself and for devices to connect to it. Ideally, you’ll want to use at least a 36W portable solar charger. It is small enough to be portable, but generates enough power to be useful, especially dealing with such a big battery. Between the solar charger and the battery, the system should be able to work through the night and a couple rainy days. It should also be able to charge a cellphone or laptop if needed.

In terms of setup, if you have a working backend system and a pre-made micro-sd card with the OS and PR-Holonet software, configuration is a matter of

You should see your WiFi access point pop up on your device. And that is it, PR-Holonet is running and ready to go!

Using PR-Holonet
Using PR-Holonet

“You keep talking about the backend, but WHAT IS IT?”

You ask. Well, good question!

Cloud Services Backend 

Cloud Services Backend
Cloud Services Backend

The backend consists of three components:

The Rockblock gateway refers to the Rock7 Core services. Rockblock being the Iridium antenna, Rock7 the company, and Core being their management portal. You’ll need to purchase credits (50 bytes = 1 credit) as well as pay the monthly activation fee ( ~$15).

From amazon you’ll need a free account to use the following services:

Finally you’ll need a phone number from Twilio that can be used for text messages. You’ll want 1 number per PR-Holonet unit as well as enough credit to support message routing.

The Rock7 Core system takes care of transmissions to and from the Iridium system. The Amazon cloud services handle processing the message, and Twilio handles routing to and from telephone numbers.

Artist's Masterpice: Data Flow
Masterful artistic rendition: Data Flow

Hopefully this write up has conveyed a bit more information about some of the technical aspects of the project. If you have questions, ask away!!

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