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Boards
The only boards I have and have tested with are the "Maxim MAX31855PMB1 Peripheral Module"(brand new, TODO: test it) and the "Unbranded MAX31855K Breakout Board". On all other boards, I have only reviewed schematics and online data. There are more out there, this list of boards is just the ones I have spent time reviewing their schematics.
Note, It appears to be a popular practice to put a pull-up resistor on Chip-Select. Three of the four boards I looked at did this. This will not work with HSPI on an ESP8266. See Troubleshooting - ESP8266 Will Not Boot for specifics.
Maxim MAX31855PMB1 Peripheral Module, Module Datasheet, Module Datasheet - Schematic page
This appears to be positioned as an evaluation board, peripheral module, and reference design. This appears to be the reference design used by other breakout boards. It goes for about $21. This is a good value when you consider it has the Type-K socket, ESD protection circuit, comprised of a duel TVS diode, pads for additional noise suppression CAPs, 4 layer board, and series resistors on the SPI Bus signals. These appear to help with noise, ringing, on the SPI Bus. Since the temperature at the end of the thermocouple wire (cold-junction) needs to be measured, I see the PCB-mounted mini Type-K jack on the board as a plus because it can help thermally couple the Type-K plug temperature to the board and thus the IC measuring the cold-junction/ambient temperature.
Usually, when I see a Manufactures's evaluation or break-out board, the price is not within reason for a hobbyist's budget. This one is competitively priced when you consider the additional features and quality. It appears to be positioned as a regular product, not as an overpriced evaluation board.
Sparkfun Thermocouple Breakout - MAX31855K, Schematic
Compared to the Maxim board, this board is missing the ESD protection circuit, and the mini thermocouple socket is an optional addition you solder on. The pads for two optional shunt capacitors in the filter circuit are also missing. From photo's this board looks like it is two layers. On the backside of the board is a ground plane. The top side has ground surrounding traces. It looks like the layout has excellent separation of the analog measurement side from the digital side. They did a good job of keeping the Analog traces away from the Digital.
The Sparkfun has a 10K pull-up on CS. See Troubleshooting - ESP8266 Will Not Boot for details.
Digilent Pmod TC1 (Revision A), Pmod TC1 Reference Manual, Schematic of the Pmod TC1
The "T+/T-" terminals only have a single capacitor for filtering the thermocouple connection.
It has a π filter on the 3.3V supply line. This is a good addition when you consider that the MAX31855 is really an analog and digital device. I think at least trying to isolating your system's digital supply noise from the MAX31855 is a good idea when you are trying to measure microvolts.
Chip-Select has a 10K pull-up resistor. See Troubleshooting - ESP8266 Will Not Boot for details.
Adafruit Thermocouple Amplifier MAX31855 breakout board, Schematic, Open source design
The Adafruit breakout board has an onboard LDO regulator and level conversion components for both the SCLK and CS SPI bus signals. Compared to the Maxim board, this board is missing the ESD protection circuit. The pads for two optional shunt capacitors in the filter circuit are also missing. It has screw-down terminals in place of a mini Type-K socket.
Regarding the resistor/diode network for performing level conversion for both SCLK and CS. I had concerns about the use of a 1N4148 instead of a Schottky Diode, this Electronics StackExchange Q/A supports my concerns. This also, will not work with the HSPI option on the ESP8266. The pull-down resistor on GPIO15 and the pull-up in the level converter create an undefined logic level. You will need to use another GPIO pin for ChipSelect. The Adafruit HUZZAH ESP8266 module will most likely do better than other ESP8266 Modules because they use a 4.7KΩ resistor for pull-down instead of 10-12K. Combined that with the voltage drop across the diode on the pull-up side you arrive at a voltage that is almost a legitimate CMOS VIL; however, for proper noise handling, you want to be at a proper CMOS VOL. Thus, I do not consider this a robust solution. For more details and better solutions, see Troubleshooting - ESP8266 Will Not Boot.
There are breakout boards that appear to be clones based on Adafruit's open-source design. The unbranded MAX31855K breakout board I have does not follow their parts list value. It uses the Torex XC6204, Mark 4B2X for the LDO regulator. I see this part often on breakout boards, display modules, and ESP8266 development boards (tangent - bad choice for ESP8266). This unbranded board uses the Torex Semiconductor's XC6204 with ~0.89μF output capacitor. Per most datasheets of similar CMOS LDOs, this value must be >= 1.0μF. The input capacitor is also missing. This is bad, especially if you used a ribbon cable to connect. When the voltage source is not near the regulator, an input capacitor is often required. This is a very common requirement for IC regulators. The datasheet calls for a minimum of 0.1μF; however, most of the test data presented was done with 1.0μF. Also, most datasheets recommend when using a ceramic to use an X7R or X5R dielectric capacitor. These are more temperature-stable.
Unbranded MAX31855K Breakout Board Change Summary
- The two ~0.5μF ceramic CAPs are almost okay. The net value falls just under 1μF. This may be due to part tolerances. To guarantee stability, add an additional CAP to make the net value, a temperature stable value over 1.0μF.
- The breakout board is missing a CAP for CIN. Add a CIN to the backside of the board where the header is connected.
- The MAX31855 is missing a 0.1μF bypass CAP. This value would have a different resonant frequency than the ~0.5μF CAP. I don't know if it matters. No harm in paring one on to the existing CAP near the chip.
- Added 150 Ohm resistors to the off-board SPI Bus connector: SS, SCK, and SDO.
- Make it more suitable for use with the ESP8266. Converted to 3.3Volt logic operation only. Removed two pull-up resistors and replace two diodes with 0-ohm shunts. With these changes, HSPI should work with GPIO15 for Hardware CS.