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Chillmon Board v0.1
Copyright 2013 Ryan Pierce, rdpierce@pobox.com
https://github.com/RyanPierce/ChillmonBoard
Component RASPBERRYPI_B / RASBERRYPI_SHIELD modified from microBuilder
library, available at
http://www.microbuilder.eu/Projects/EagleFootprintLibrary.aspx
OVERVIEW
This board is a Raspberry Pi shield designed to be used with the Chillmon
application, available on Github at https://github.com/eastein/chillmon for
the purposes of providing temperature control for fermenting beer!
INPUTS
J1-J8 are analog temperature sensors. The center pin is the signal, and the
end pins are power (+3.3V) and Ground. Power is indicated with the +
symbol.
Each sensor connects to a channel on an MCP3008 10-bit ADC. This is
connected to the Raspberry Pi as per the Adafruit tutorial available
here: http://learn.adafruit.com/send-raspberry-pi-data-to-cosm
Note that 4 of the Pi's GPIO pins are used for bit-banging SPI; the Pi's
native SPI is not used.
JP1 is a 0.1" header to determine the Vref voltage for the ADC conversion.
Two choices are provided; jumpering the left two pins provides a precision
1.0V reference, while jumpering the right two pins connects the 3.3V power
supply from the Pi. The regulation of this power supply is unknown. Using
1.0V leads to a lower temperature range (maximum is 50C / 122F) but provides
for a higher temperature resolution.
JP9 is a port for a chain of Dallas Semiconductor OneWire temperature
sensors, especially the DS18B20. Adafruit provides a tutorial here:
http://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing
As above, the center pin is the signal, and the end pins are power and
ground. Power is marked with a + symbol. Many DS18B20's can be connected in
parallel. Note that the Adafruit Occidentalis distribution for the Raspberry
Pi includes the OneWire kernel driver. At present, the Chillmon software
does not support this. The board includes the 4.7k pullup resistor, which
is required for OneWire.
OUTPUTS
J10, J11, and J12 are digital outputs connected to GPIO pins on the Pi,
specifically GPIO17, GPIO21 (for Rev1 Pi) / GPIO27 (for Rev2 Pi), and
GPIO22 respectively. Rumor has it that the change between Rev1 and Rev2
is corrected within the Python library. Each pin has a 10k pulldown resistor,
which is critical because the Pi initializes all pins in input mode; voltage
on them can float high enough to trigger solid state relays, which will
quickly burn out an air conditioner compressor. Currently, the Chillmon
software assumes an air conditioner is connected to J10, however in the
future we would like to add a heater, as we have found that the temperature
at Pumping Station: One in the winter often drops below our target ale
fermenting temperature. Note that these outputs are current limited by the
Pi; it can directly drive a solid state relay.