Mesh networking for sensor grids

Mesh networking board by Daniel on Hackaday.io:

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Low-power mesh networking for small sensor grids

Tiny MQTT-interoperable broadcast mesh networking with simple radios

This project is a low-resource mesh networking stack and mote with battery-powered routers based on state synchronization. The target is for the stack to use less than 2kb SRAM. Nodes use low power listening and an adaptive gossip protocol to synchronize key/values pairs with each other without relying on explicit routing or per-node addressing.

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For example, a light might transmit (/lamp, {“state”:”on”}) to the mesh. Write (/lamp, {“state”:”off”}) to the mesh, and the lamp application will notice. The powerful but simple state synchronization primitive allows you to update the state of the mesh to update the world, and update the state of the world to express the same on the mesh. Trivially bridged to a private MQTT server and managed with off-the-shelf MQTT applications.

The design files and source code are available on Bitbucket:

dholth/mesh

Mesh networking for sensor grids

Castellated Edges

Castellations are small plated edges, typically used for making circuit boards into small PCB modules. These are often seen on wireless modules, such as the ESP8266-12E.

While we don’t offer full support for castellations, they can be fabricated if you don’t mind a few minutes of rework and verification of the PCBs.

Design Considerations

It’s helpful to include a fallback hole near the edge. The ESP8266-12E boards, are a great example here. The extra via allows easy connecting of wires for rework, and makes it easy to salvage a module if the fabricated PCB doesn’t turn out perfectly.

ESP2866-12E
ESP2866-12E, available at Adafruit.com

Indicating in the design file

Castellations are simple to call out in most design tools. Simply include a via on the PCB, so the board outline goes through it.

However, due to our panelization process, the castellated vias must be indicated with round pads for copper and stop mask. The pads must also not extend more than 40 mil from the board edge. Square pads or pads that extend far beyond the edge will be trimmed, and the via will not be plated.

It’s also helpful to use a 10 mil wide line for the board outline. With our milling tolerance of 5 mil, this provides a good visual indicator of where the physical board edge might be. The fabricated edge can be anywhere within that line. This is very helpful for fine-pitch castellations with smaller holes.

Callout as seen in a design tool
Callout as seen in a design tool

Rectangular castellations can be made by using vias with round pads as noted above, and adding overlapping rectangular SMD pads. Since these pads are inside the board outline, they will not be trimmed, and will provide additional area for soldering (see below for example).

Cleaning up the final boards

We make a best-effort to minimize support tabs on castellated edges, but it sometimes happens. In these cases, you’ll need to file the tab off of your edge.

Additionally, the via plating may not be fully removed during the milling process. In some cases it’s smashed next to the edge, where it can cause unwanted connectivity between vias. In others, it’s smashed inside the via, where it will prevent good solder flow. A fine point file or hobby knife will help remove excess plating.

An unreworked castellated PCB, with visible plating stubs
An unreworked castellated PCB, with visible plating stubs
Another version, with tabs on castellated edge and modifications for rectangular pads
Another version, with tabs on castellated edge and modifications for rectangular pads
Castellated Edges

SIS-2 Universal Remote Receiver

Jeremy Cook writes on the Tindie blog about this IR receiver board by Atomsofttech:

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SIS-2 Universal Remote Receiver

When you think of a “universal remote,” you generally picture an infrared (IR) emitter that can be setup to control your TV, AV receiver, and any other number of devices that work using IR signals. On the other hand, what’s to keep someone from doing the opposite, and having a universal receiver that can be programmed to accept codes from a remote that you just have lying around?

Watch the receiver board in action:

SIS-2 Universal Remote Receiver

SoundBeacon

Patrick Van Oosterwijck created an audio BLE beacon that can be activated by the vision impaired to find exact locations of doorways, bus stops, crosswalks, and more:

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SoundBeacon

The idea is that a blind person uses a navigation app, and can query to see “what is around”. In the list of beacons that are around, they can tap the one they want to know the location of and it will start to produce an audible signal for a short time.

The BLE module is configured as an iBeacon and allows connections. It has a battery service and an “Immediate Alert” (AKA “Find me”) service.

Patrick used the following to build the prototype:

  • A 550 mAh 3.2 V LiFePO4 cell
  • A #LiFePO4wered/Solar1 prototype to charge the battery
  • A 5.5V, 0.6W monocrystalline solar cell
  • A Silicon Labs (formerly BlueGiga) BLE113 module
  • A beeper that works very badly (better solution needed)
  • And a IP65 enclosure

xorbit has shared the booster for loud piezo beeper on OSH Park:

PiezoBoost

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Order from OSH Park

SoundBeacon

Pidgeon 1 Sub-GHz Radio

Pidgeon 1 on Crowd Supply is a sub-GHz radio with 500 mW transmission power, RS485 networking interface and a STM32F0 microcontroller:
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Crowd Supply: Pidgeon 1

No more restrictions from high level software! Access the lowest level of digital radio transmission with this programmable sub-GHz wireless module.

Hardware Specifications:

  • Radio – CC1120 + CC1190
  • Controller – STM32F051K6
  • FTDI USB interface – FT234XD-R
  • RS485 interface – LTC2850IDD
  • Buck converter – RT8010GQW
  • SMA connector for antenna
Pidgeon 1 Sub-GHz Radio

14-bit 80MSPS ADC for SDR experiments

Eric Brombaugh designed this ADC board for RF signals:

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RXADC_14 Pmod

This is an ADC designed for use in digitizing RF signals with up to 40MHz bandwidth and 80dB SNR. The form-factor is compatible with a dual-connector Digilent Pmod so that it can be used with commonly available FPGA development boards to build a variety Software-Defined radio functions.

Features:

  • ADC14C105 14-bit 105MSPS RXADC.
  • Onboard 3.3V Regulator (5V input)
  • Filtered Analog 3.3V Supply
  • Onboard 80MHz clock oscillator
  • Digilent-compatible 2-connector Pmod interface
  • 50-ohm SMA input – 2.5Vpp ~= 0dBfs

emeb has shared the board on OSH Park:

14-bit 80MSPS ADC for SDR experiments

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Order from OSH Park

14-bit 80MSPS ADC for SDR experiments

Star Trek Communicator Badge

Joe Crop is a creating a real life version of this famous sci-fi device:

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Star Trek Communicator Badge

In the true spirit of Star Trek, this communicator badge is completely autonomous, while fitting in the form factor of an original badge

Star Trek was known for dreaming up technology that was deemed nearly impossible given the limitations of the technology for the day. Having a small badge that could send audio across vast distances seemed out of the realm of possibility during the late 1980’s. This project’s aim is to use modern technology to provide nearly all the features of visionary tech, namely:

– Tap to connect and communicate instantly
– Long range (from orbit to planet surface)
– Small form factor (of an original TNG badge)
– Fully autonomous (no cell phone or base station needed)
– No external power source (i.e. battery powered)

joecrop has shared the board on OSH Park:

Star Trek Communicator v2p1

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Order from OSH Park

Star Trek Communicator Badge