PT100 and PT1000 Breakout Board with MAX31865

[BlackBrix]

Hi,
I just found this project on tindie and I think I should order some ...
from the arduino library I can see that it is maybe only supporting temperatures grater than 0°C (?) in an exact way ?
(cause the RTD_C constant is not used ?)
It would be great to fix this (or maybe I can extend the library myself) for temperatures below 0°C
The formulas are quite simple, I found them here --> https://24max.de/elektronik/Pt100-Formulas.pdf

[Charles]

@BlackBrix
What to you mean by greater from 0°C, it works fine on my tests

But may be you meant lower than 0°C ? To be honest I didn't tested that one, I need to check, but I think it should works

[gruenst]

Hi Charles,
I tried your breakout board with the same setup I used for mine, and it works. So it's not the software, and not the Arduino Feather board. Must be the difference in setup of the breakout board.

I solved an issue with the ground pin, so DVDD and VDD now both show 3.3V.
Further, I connected Force2 with Force+ instead of Ground (different to the diagram above), to adapt it to yours. Which doesn't change anything. It shouldn't be the difference in packaging, as SSOP takes less power than your TQFN. So the only difference I see are the two ferrite beads, which I don't use.
Which ones do you use? Or would you see a mistake I made with the assembly shown above?

Thanks!
Stefan

[Charles]

@gruenst
the ferrite board (470 Ohm) are used to do

• FB1 Filtering AVDD
• FB2 Filtering AGND

But you can bypass them, ie put a wire instead, should also work

[Fernando Vinícius G. Magro]

Hi CHARLES,
Can you give me information (specs) about the SMD FB1 and FB2 ?
There is a Mouser or Digikey part number for this item?
Thanks

[Charles]

@Fernando-Vinícius-G-Magro
the Mouser link was in my previous response but it's a 470 Ohm classic Ferrite Board
http://eu.mouser.com/Search/ProductDetail.aspx?R=BLM18PG471SN1Dvirtualkey64800000virtualkey81-BLM18PG471SN1D

[Erik van Os]

@Charles
Hi charles,
have a question about your nice project, can I use it also for a Raspberry PI 3B?
thanks Erik van Os

[Charles]

@Erik-van-Os
thanks, yes for sure you can use it with RPI3 but you'll need to adapt the code, may be using WiringPi library.

[Roelof Loots]

Hi Charles, would it be possible to connect more than one of these boards to a single arduino uno somehow? I just bought 3, and would just like to know if it would be possible to read temperatures from 3 x RTD's

[Charles]

@Roelof-Loots
Yes it's possible, each RTD board just need to have it own chip select pin (and led pin if you use it) all SPI pins can be shared (MOSI, MISO, SCLK), that the goal of SPI

Take care your Arduino MUST be only 3V3 because RTD boards are 3V3 only, if your arduino is 5V you need level shifter and with 3 RTD boards it will be a real pain....

[Roelof Loots]

@Charles - Thx for that...im using a arduino uno, and looks like its got 3V3, so I should be able to do it correctly using a breadboard, else ill just get logic level converters.

[Charles]

@Roelof-Loots
Take care, even if your Arduino Uno has a 3.3V pin available (fine to power RTD), all I/O need also to be full 3.3V (MOSI/MISO/CS/CLK) which may not the case. IT's better to have a full 3V3 Arduino (even at 8MHz)

I'm using this one that have a switch to pass full board to 5V or 3V3 https://www.seeedstudio.com/Seeeduino-V4.2-p-2517.html or just find on ebay Arduino Pro Mini 3.3V USB

[Vishi100]

Hi! I'm trying to interface MAX31865 (PT1000) to STM32F334 controller (Nucleo64) (Cortex M4) board. I used the Arduino codes from github and coded the STM32F3 controller. Both the sensor and the controller are tested & working fine. But when i read from MAX31865, I'm getting the maximum values in all the registers. Can i get plz get some help as to what might have gone wrong??

[Fernando Vinícius G. Magro]

Hi Charles, the IRQ (DRDY pin) of Max31865 need to be wired?
I can presume that it can be useful to trigger an interrupt when a conversion is completed, but it is not mandatory. Can i left it unconnected ?

[Charles]

@Fernando-Vinícius-G-Magro
The IRQ line should be wired only if you need an interrupt. So it's not mandatory don't worry you can left it unconnected.

[Rolando]

Hi Charles, what function R3 is supposed to do? And why 390Ω instead of 400Ω as recommended on Maxim datasheet? Thank you in advance.

[Charles]

@rolando do you mean R2?

you use R2 for PT100 (R4 unsuded) and R4 for PT1000 (R2 unused)

it's 390 and 3.9K because sourcing was easier with these values

It's no problem, it's adjusted to correct valuee into the code look for an example here

[cbparks]

Thank you for the very fine design. Would you please mind helping with the sketch changes to read temperature in fahrenheit? Thank you.

[cbparks]

Figured out the fahrenheit question but with a PT100 the ohms do not read correctly. Changed all the rtd.raw_resistance to rtd.resistance. That corrects the correct ohms reading in the serial monitor but not on the oled display. Appreciate any suggestions on how to correct. thank you.

[admin]

@cbparks
The reading and display depends on reference resistors soldered on your boards, in my design it's 390 for PT100 and 3900 for PT100, it's declared here and the only place it should be

Then declare if you want to use PT100 or PT1000 here