I'd like to know my options for connecting 4-5 temp probes to an arduino. I've been using and am familiar with the max6675 library, so prefer to use that if possible, just not with 4 or 5 shields/chipsets/whatever they're called. I thought maybe a shift register would work, but wasn't sure since the max6675 needs around 500 milliseconds to communicate w/ the probe...so if I had 5 probes to 1 chip/shield/whatever you call it...I'd be looking at a delay of at least 2.5 seconds between readings. I'd rather keep that closer to 1 second between readings, so I'm not sure that's an option.
So what are my options for hooking up 5 k-thermocouples to a single arduino mega?
I've done multi-temp cards. Used a MAX31856 chip for each probe that was connected, read them sequentially using SPI.transfer commands. Use RTD type probe vs K-type thermocouple
The conversion time of the MAX6675 (220ms maximum, btw) just refers to how frequently the temperature can be read. That conversion happens in the background, so to speak, while you could be transferring data from other chips. It supports a 4.3MHz SPI speed so there shouldn't be any problem reading quite a few sensors at a rate of four times per second.
Putting that another way, the limitation on speed is that the CS pin for any single chip has to be high for at least 220ms.
You should probably mention what temperatures you're dealing with. If you don't need the high temperatures that require thermocouples there are a lot of less expensive options.
You don't say just how the probes are being used, but if you are interested in waterproof, there are ones like these DS18b20 from Amazon (and other places - this was just what I got a while back). They do have a maximum conversion time of something like 750ms but you could as others have said start the conversion then come back and read them later. You can have multiple ones on the same 1 wire interface.
CrossRoads:
I've done multi-temp cards. Used a MAX31856 chip for each probe that was connected, read them sequentially using SPI.transfer commands. Use RTD type probe vs K-type thermocouple MAX31865 Datasheet and Product Info | Analog Devices
Thanks for the heads up on the 6675, and the info on the 31856. That's what I'm looking for. Why go with the RTDs over the Ks? I was under the impression the Ks were more accurate and had a broader reading range?
