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Mespelare VSCP node

· David Steeman · Electronics, VSCP, Mespelare VSCP
Mespelare VSCP node

The Mespelare node is a VSCP board based on the Hasselt board by kurt_sidekick, used to read a Niko 6-way potential-free button set, and control it’s 6 indicator LEDs as well as 6 outputs (teleruptors).

It is intended to serve as a general base node for further development of custom functionality, without each time having to re-invent the wheel. To reach this goal most processor pins are broken out to pin headers, which either connect to the Niko 6-button switch and teleruptors, or are populated with pin headers so another board can be piggy-backed onto the base node (Arduino shield-style). Using the same base board to build new applications on offers the following advantages:

  • A stable, well-debugged and known-working base platform
  • The possibility to do bigger board production runs

Mespelare VSCP node

Features
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The Mespelare VSCP board has the following features.

7 inputs
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6 inputs are intended to read the button-presses on the Niko 6-way push-button set. A seventh input was added just because we can, and to provide an extra input in case the base board is used in another application. The inputs are filtered using a low pass filter on each channel to prevent HF interference from reaching the microprocessors’ inputs.

2 x 7 outputs
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6 outputs are in are intended to control the LEDs that are integrated in the Niko 6-way push-button set. A seventh output was added just because we can, and to provide an extra output in case the base board is used in another application.

6 outputs are in are intended to control up to 6 teleruptors. A seventh output was added just because we can, and to provide an extra output in case the base board is used in another application.

One wire interface
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The micro-controller’s OneWire interface was broken out onto a pin header.

On board peripherals:
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  • 1 button (which can be used as a VSCP button or for troubleshooting)
  • 1 LED (mainly for troubleshooting purposes)
  • Buzzer (mainly for troubleshooting purposes)
  • A footprint for a DS18B20 temperature sensor.

On board status LEDs:
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  • RX (CAN bus)
  • TX (CAN bus)
  • Power status
  • Status (VSCP)

Power supply
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  • On-board Microchip MCP1804 power regulator
    • 6.3-28V input
    • 5V 150mA output (the low power output means extension boards will require a separate regulator)
  • Protected by a 200mA poly-fuse and crowbar circuit
  • Filtered against power rail noise
  • Proper decoupling for all chips on the board

CAN bus
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  • A properly filtered, protected and impedance-matched bus connection
  • Controlled by a Microchip MCP2551 bus interface chip

Expansion / ICSP header
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A single “expansion/ICSP header” combines the ICSP signals with a OneWire and I²C bus. The order of the first 5 pins on the header are compatible with the PICkit pin-out.

PCB mounting
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4 mounting holes in the corners for easy mounting, M3 size.

Mespelare VSCP node

Printed circuit board
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Design criteria
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  • Possible to produce at home using a photo-transfer process, so that the board can be prototyped and tested at home. This means:
    • PCB size must not exceed Eurocard dimensions
    • a minimum of via’s
    • no tight spacing of components and tracks
    • a minimum of through-hole soldering on the top layer
  • Addition of an integrated set of LEDs and buttons on the first prototype

I had the PCB professionally produced at SeeedStudio, it cost only 1.83€ per board for 30 boards shipping included.

Mespelare VSCP node

Testing
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Until we write custom firmware for this node, we’ll be testing the node bit by bit.

Quick test
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Although the firmware for the Hasselt node isn’t compatible with the pin-out used by the Mespelare node, some functionality does work. If you load the Hasselt hex file the node will be visible on the bus. Buttons 1 will send events as well.

Hasselt test firmware hex

Hardware tests
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I use these detailed test programs to check separate parts of the hardware to see if they function correctly. Download a zip with the source code and pre-compiled HEX file.

  • Blink-a-led : generates a buzzer tone at start-up, and then randomly blinks all LEDs on the board
  • Button & leds: each press of the init button toggles each LED on the board, one after the other
  • Inputs : toggles the corresponding outputs when pushing a button
  • CAN toggle : puts a 50Hz square wave on the CAN bus pins
  • DS18B20 Onewire : beeps the beeper when a temperature change is detected
  • DS18B20 Onewire serial : outputs temp value to serial (9600, 8n1, no flow), and beeps the beeper when a temperature change is detected
  • Button : sounds the buzzer when the misc button is pressed (board revision v6 only)

Downloads
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Schematic & PCB layout

Source code: see the article Mespelare VSCP firmware - first compile

Resources
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