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What

A voting device, similar to edubuzzer but with the design-goal of being super-cheap.


Hardware

bare PCB, no container (yet)

MCU

STM32F100C8T6

Reasons:

  • Cheap
  • Powerful (up to 24MHz), Cortex-M3
  • Lots of GPIOs
  • Small (LQFP48)
  • 3.3V levels

Alternatives:

  • STM32F0xx
  • Freescale Cortex-M0
  • MSP430G2553
  • RFD22301 (probably far too expensive, but it includes the RF stuff)
  • ATmega328P @ 3.3V, 8MHz

RF

nRF24L01+ module

some info for using them with Arduinos

Reasons:

  • Cheap
  • Small
  • Relatively low-power
  • Easy to use
  • Lot of libraries for it
  • Supports point-to-point, broadcasts and multiple channels
  • Special module versions available with ranges of up to 1100m
  • Uses 3.3V levels

There are a lot of modules with that chip available. Most of them use a 2x4pin 0.1" connector with a standard pinout. There are also much smaller SMD modules available, but these are more expensive and do not seem to have a standard pinout or layout.

Alternatives:

Display?

Nokia 5110 display

Reasons:

  • Cheap
  • Small
  • Low-power
  • Lot of libraries for it
  • Can mount directly to the PCB, no expensive/rare connector required
  • Uses 3.3V levels

Alternatives:

  • Just some status LEDs (takes a lot of power)
  • Sharp Memory Display
  • Liquid Crystal display without a backlight
  • Two flipdot-dots?

Buttons

5x5mm button

Reasons:

  • Cheap
  • Large enough for humans to handle

Alternatives:

too many to list

Leds

None

Reasons:

  • LEDs require a lot of power
  • Not a lot of expressiveness with them

Power

Coin Cell: CR2032, 3V

Reasons:

  • Cheap
  • Low self-discharge

Unsolved problems:

  • Does not deliver a lot of power (~0.1mA per spec)
  • Not a lot of capacity

Alternatives:

  • AA battery (large, but cheap and easily available — only delivers 1-1.5V though)
  • 2xAA battery for 2-3V (very large!)
  • Lithium Polymer Battery (like the one used in the Magic Shifter)
  • Solar Panel

BOM

Table here..



Basestation

RaspberryPi

NRF shield

Raspberry Pi-to-nRF24L01+-Module Adapter

Who

Overflo

anlumo