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Is it worth it to design a custom device? #9

Description

@ambergristle

Demeter should be as accessible (low cost and infra-agnostic) as possible. The Oplà IoT Kit is currently listed at €145, and sold out. It also funnels users into the Arduino ecosystem, which is not a neutral choice.

To some extent, this issue assumes that Demeter should own the client, rather than allowing users to add custom calls to their own code.

Maybe the first step should be writing platform-agnostic firmware that can be installed + run on any microcontroller.

Opportunities for improvement

  • Replace obsolete components with replacements.
    • May be done by Arduino eventually, but some newer sensors are cheaper and/or more accurate.
  • Downgrade to avoid paying for unused features.
    • Do Demeter users need gesture sensing? Gyro readings?
  • Optimize generally for resources:
    • Do devices need buttons, a display? How much space does it need to occupy?
    • Can power draw be reduced?
  • Differentiate between "home" station and plot-specific devices.
    • No need for full device/sensor set if just taking specific moisture readings.

Considerations

  • Does Demeter just provide the circuit design? a PCB spec?
  • What are the costs/implications of custom PCB printing?
  • Should Demeter mass-manufacture devices?
  • The retail (required) component cost is ~ $64.20
    • How much of the difference is other components (e.g., gyro)?

Current

Component Role
MKR WiFi 1010 WiFi + Bluetooth-capable microcontroller board
HTS221 Temperature and Humidity
LPS22HB Air Pressure (and Temperature)
APDS-9960 Light, proximity, and gesture sensing

Component comparison [WIP]

Components are typically available in two forms: 1) as a standalone sensor, and 2) mounted on a breakout.

Breakout-mounted components will be easier to work with during design and development, and are more accessible to a wider audience of users (supporting the DIY case).
At scale, mass-producing custom PCBs that integrate the standalone components directly may be more space efficient or cost effective.

Prices below link to Adafruit breakout-mounted components, and reflect individual unit cost.

Microcontroller

Component Price Notes
MKR WiFi 1010 $39.80 Current

Networking

Component Price Notes
- - - -

Temperature & Humidity

Component Price Notes
HTS221 $9.95 Current; Obsolete
SHT40-AD1B $5.95 Replaces HTS221 *
DHT20-AHT20 $4.50 *
SHT45 $12.50
SHT31-DIS-B $13.95
BME688 $19.95 Includes air pressure

Air Pressure

Component Price Notes
MS8607 $14.95
BME280 $14.95
LPS22HB $6.95 Current
LPS25HB $9.95

Light

Component Price Notes
APDS9960 $7.50 Current; Includes gestures
VEML7700 $4.95 *
BH1750 $4.50 *

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