This was a project begun last winter in the hopes of having an array of thermocouples to monitor my old woodstove when operating it. Well, I never got around to finishing it, but I have a fancy new woodstove as of this fall, and I would love to monitor its temperature curves likewise!
This BoosterPack is fancied as a baseboard plugging underneath the LaunchPad, with four holes for mounting studs in case I ever decide to fix it inside a permanent enclosure (probably one made of aluminum due to the heat). I could have pushed the Thermocouple terminal blocks out a little further to fit more launchpads, as I feel this is a bit tight. I chose a Tiva-C LP for my pics because it fits nicely but the BoosterPack is designed with low-power features, contrary to the MAX31855’s own design.
This BoosterPack features the Maxim MAX31855 thermocouple receiver chip; this is a precision IC with built-in ADC and digital logic which performs continuous conversions of the thermocouple data and exposes the latest data at the master MCU’s demand over SPI.
As the MAX31855 never really “shuts down”, I have introduced logic to allow the MCU to switch on/off the entire thermocouple (MAX31855) power domain, utilizing a TI TXB0108 Level Shifter as a bus transceiver to disconnect all the SPI and four Chip Select lines from the MAX31855’s to prevent parasitic power from the I/O lines from clandestinely powering the chips when they’re not needed.
TI TPS27081A positive-logic PFET power switches are used to switch the Thermocouple power domain on/off and for slew-rate control of the TXB0108’s OE pin. (I bought a bunch of these for cheap from avnet a couple years ago, figured I should use them!)
For more detail: Monitoring Woodstove Temperature With A MAX31855 Quad Thermocouple BoosterPack
