MAX31865/rpi wiring question

[frontiercdk]

Hey Guys,

Hope your week is going well.

I plan on finishing the wiring on a fermentation controller this weekend. I am using a raspberry pi and the craftbeerpi software. I am wiring up three max31865 breakouts, so I can use rtd's.

Which wires on the max31865 can share pins on the raspberry?

 

[M54B25]

I, too, am interested in a definitive answer on this. My understanding is the CS wires are the ones that get their own GPIO pin while the rest can be shared.

Take this with a grain of salt, however, as I haven't yet been able to get a single max31865 + pt100 to register correctly in Craftbeerpi. Can someone confirm?

 

[day_trippr]

^That^ is correct: on the SPI "bus" the one signal that differentiates between slave devices is the CS signal. If you have multiple 31865's they can share all power/gnd/signal connections save for CS - each device needs a unique host pin for their respective CS inputs...

Cheers!

 

[frontiercdk]

Thank you for the response.. got er hooked up and it worked great.

 

[frontiercdk]

I thought I would attach the wiring I used. Forgive my schematic drawing skills!

 

[M54B25]

Thank you very much for your schematic! It solved my issue as well. As someone new to the raspberry pi + hardware world, I didn't realize GPIO pin #s were different from the pi's pin #s... I apparently had a very well grounded sensor hooked up to a couple random GPIOs that the software didn't care about.

 

[EyeBrew]

I thought I would attach the wiring I used. Forgive my schematic drawing skills!
View attachment 627868

Hi, thanks very much for the info. I have the inputs wired from the chip to the pi as you show. Can you explain the output? I thought the output would go to the SSR with one wire to ground (-) and the other to a GPIO pin for (+). Very new to this so any help is appreciated.

 

[frontiercdk]

They do...

I forgot to attach all of the schematic. I am at work, but when I get home I will post them. I am using 6 ssd's, so I took one wire (ground) from the ground on the pi and jumped it from one ssd to the next. The positives I ran from gpio's to each ssd.

 

[EyeBrew]

They do...

I forgot to attach all of the schematic. I am at work, but when I get home I will post them. I am using 6 ssd's, so I took one wire (ground) from the ground on the pi and jumped it from one ssd to the next. The positives I ran from gpio's to each ssd.

thanks, really appreciate it. Also, the reading from Craftbeerpi3 from my temp probe says 1811.42 F. I assume that is some default value and says something is not hooked up correctly? Let me know if you have any ideas about that.

 

[frontiercdk]

Ok,

Here is my full schematic. They carry over from left to right page 1 to 3.

 

[frontiercdk]

The 1811.42 F reading is the reading I got when the pt-100 sensor was not hooked up at all. Make sure you use the gpio pins I used. I think I read somewhere the software requires certain pins for the max 31865.

let me know how its going

 

[frontiercdk]

Side note on the 1811.42 F reading... When I first ran the first two pt-100 sensors they gave this reading for a while. It would read 1811.42 for a while then it would read correct temp for a while. It finally just read 1811.42. I left it run and after quite a while it started reading correctly and been doing so for a couple weeks now. I have no idea why. I hooked up the last pt-100 sensor a couple days ago and it did the same thing. It took running it overnight for it to read correct temps. I emailed Auber Instruments and Adafruit. Auber said the pt-100 required no break in period or anything like that. I sent my email to the wrong department at Adafruit and they responded by telling me to use their "community" blog page for technical questions. I did not follow up (the reading were perfect by then).

Anyway... If ya get the 1811.42 try letting it run for a couple days and check your logs for that sensor. I am curious if yours does the same thing.

 

[EyeBrew]

Side note on the 1811.42 F reading... When I first ran the first two pt-100 sensors they gave this reading for a while. It would read 1811.42 for a while then it would read correct temp for a while. It finally just read 1811.42. I left it run and after quite a while it started reading correctly and been doing so for a couple weeks now. I have no idea why. I hooked up the last pt-100 sensor a couple days ago and it did the same thing. It took running it overnight for it to read correct temps. I emailed Auber Instruments and Adafruit. Auber said the pt-100 required no break in period or anything like that. I sent my email to the wrong department at Adafruit and they responded by telling me to use their "community" blog page for technical questions. I did not follow up (the reading were perfect by then).

Anyway... If ya get the 1811.42 try letting it run for a couple days and check your logs for that sensor. I am curious if yours does the same thing.

Thanks for the additional schematic and the info about the temp reading. I have double checked the wiring and everything seems to be hooked up correctly. I will try to let it sit a while. If that doesn't work I will review the work I did on the Max chip. Could be my rookie soldering skills

 

[frontiercdk]

Thanks for the additional schematic and the info about the temp reading. I have double checked the wiring and everything seems to be hooked up correctly. I will try to let it sit a while. If that doesn't work I will review the work I did on the Max chip. Could be my rookie soldering skills

Yep. The soldering was hard for me as well. I had to go to harbor freight and pick up one of those table top magnifier/light things to get it done, especially removing the trace between those two tiny blocks...

Also... use the craftbeerpi 3. I started with the 2 version... don't use it.

 

[EyeBrew]

Yep. The soldering was hard for me as well. I had to go to harbor freight and pick up one of those table top magnifier/light things to get it done, especially removing the trace between those two tiny blocks...

Also... use the craftbeerpi 3. I started with the 2 version... don't use it.

I did a simple program to turn on an led and figured out I had the ribbon, attaching the breakout board to the breadboard, attached backward. I fixed that and was able to get the led to turn on so I believe everything is attached to the pi correctly now. I also examined the MAX chip and ensured the trace wire was cut and touched up some soldering. I reassembled everything and double checked wiring is attached per schematic. Now instead of 1811F the temp is just bouncing around randomly. (See below) If I unplug the sensor I get a steady 1811F so I apparently am getting some reading from the sensor to the pi. It has been over 24hrs, not sure what else to check. Any ideas on what would cause the random temp readings?

6/9/2019 9:35 342.49
6/9/2019 9:36 -59.8
6/9/2019 9:36 -270.4
6/9/2019 9:36 -428.8
6/9/2019 9:36 -148
6/9/2019 9:36 902.39
6/9/2019 9:36 1234.41
6/9/2019 9:36 -2.2
6/9/2019 9:36 -241.6
6/9/2019 9:36 990.28
6/9/2019 9:36 273.62

 

[EyeBrew]

Here is a sample of the App Log if this helps

6/9/2019 14:13 135 - INFO - emitting event "SENSOR_UPDATE" to all [/brew]
6/9/2019 14:13 143 - INFO - fd67dc8b3c6f4286a5becdd2f7b40bff: Sending packet MESSAGE data 2/brew ["SENSOR_UPDATE" {"config":{"ConfigText":"[0xD2] - 3 Wires Auto" RefRest:"430" csPin:"13"} hide:0 id:1 instance:{"unit":"\u00b0F" value:1440.34} mode:"P" name:"PT100" type:"PT100"}]
6/9/2019 14:13 966 - INFO - fd67dc8b3c6f4286a5becdd2f7b40bff: Received packet PING data None
6/9/2019 14:13 968 - INFO - fd67dc8b3c6f4286a5becdd2f7b40bff: Sending packet PONG data None
6/9/2019 14:13 246 - INFO - emitting event "SENSOR_UPDATE" to all [/brew]
6/9/2019 14:13 254 - INFO - fd67dc8b3c6f4286a5becdd2f7b40bff: Sending packet MESSAGE data 2/brew ["SENSOR_UPDATE" {"config":{"ConfigText":"[0xD2] - 3 Wires Auto" RefRest:"430" csPin:"13"} hide:0 id:1 instance:{"unit":"\u00b0F" value:-257.8} mode:"P" name:"PT100" type:"PT100"}]
6/9/2019 14:13 357 - INFO - emitting event "SENSOR_UPDATE" to all [/brew]
6/9/2019 14:13 365 - INFO - fd67dc8b3c6f4286a5becdd2f7b40bff: Sending packet MESSAGE data 2/brew ["SENSOR_UPDATE" {"config":{"ConfigText":"[0xD2] - 3 Wires Auto" RefRest:"430" csPin:"13"} hide:0 id:1 instance:{"unit":"\u00b0F" value:334.28} mode:"P" name:"PT100" type:"PT100"}]
6/9/2019 14:13 468 - INFO - emitting event "SENSOR_UPDATE" to all [/brew]
6/9/2019 14:13 476 - INFO - fd67dc8b3c6f4286a5becdd2f7b40bff: Sending packet MESSAGE data 2/brew ["SENSOR_UPDATE" {"config":{"ConfigText":"[0xD2] - 3 Wires Auto" RefRest:"430" csPin:"13"} hide:0 id:1 instance:{"unit":"\u00b0F" value:1108.62} mode:"P" name:"PT100" type:"PT100"}]
6/9/2019 14:13 579 - INFO - emitting event "SENSOR_UPDATE" to all [/brew]
6/9/2019 14:13 586 - INFO - fd67dc8b3c6f4286a5becdd2f7b40bff: Sending packet MESSAGE data 2/brew ["SENSOR_UPDATE" {"config":{"ConfigText":"[0xD2] - 3 Wires Auto" RefRest:"430" csPin:"13"} hide:0 id:1 instance:{"unit":"\u00b0F" value:-205.6} mode:"P" name:"PT100" type:"PT100"}]

 

[frontiercdk]

I think there is a "resistor" setting for the probe/max board. I set mine to 430 I think. I will check this evening. Did you set it?

 

[day_trippr]

Was leaving the MAX "3V3" pins unconnected just an documentation error?
Both the VDD and DVDD pins need to be connected to 3.3V...

Cheers!

 

[frontiercdk]

I believe the 3v3 is not needed (mine is not hooked up). I understand it to be an extra output voltage source, if you need to run something else.

 

[EyeBrew]

I think there is a "resistor" setting for the probe/max board. I set mine to 430 I think. I will check this evening. Did you set it?

Yes, I have had mine set to 430. The temp probe is brand new. Maybe I fried something on the Max. I may re-order and try again.

 

[day_trippr]

I believe the 3v3 is not needed (mine is not hooked up). I understand it to be an extra output voltage source, if you need to run something else.

Interesting. Actually, surprising.
This is what the Maxim spec shows:

DVDD: Digital Supply Voltage Input. Connect to a 3.3V power supply. Bypass to DGND with a 0.1μF bypass capacitor.
VDD: Analog Supply Voltage Input. Connect to a 3.3V power supply. Bypass to GND1 with a 0.1μF bypass capacitor.

I can't recall ever using a similar part that didn't require both voltage inputs to be connected. Generally the "digital" supply input is for the interface logic (which can be "bouncy") while the "analog" input is for the ADC (which you want to be as "quiet" as possible). But I suppose there's alway a first lurking out there

Cheers!

 

[EyeBrew]

Yes, I have had mine set to 430. The temp probe is brand new. Maybe I fried something on the Max. I may re-order and try again.

I received a new Max and wired it up. I am not getting random temps anymore. However, the temp is way off. It is reading 1325F. It is holding steady within a degree. When I grab the temp probe in my hand the temp starts rising and falls back when I let go. Any idea what would make the reading 20x of what it should be?

 

[frontiercdk]

I bet your sensor resistance is not 430... find the correct resistance and make the change... bet it works

 

[BrunDog]

Sensor resistance is nominal: Pt100 is 100 ohms at 25 degs C.

 

[frontiercdk]

I think there is another resistor used to check the wire resistance on a three wire pt100. It is the one that you have to manually enter into craftbeerpi. I am using a pt-100, have this field set to 430 and mine works great, but I believe there a major variances on the value of this resistor.

 

[EyeBrew]

I just wanted to close this out. After further inspection I believe it was my poor soldering skills. On the 24 3 pad, some solder was touching the pad that I had broken the wire to, thus reconnecting it. I reheated the solder and was able to remove it. I plugged the chip in and it is working fine. thanks for everyone's help! Going to attempt my first all grain batch this weekend.

 

[frontiercdk]

That us awesome.... hope your 1st all grain is awesome as well!