Hi all,
I stumbled upon this project by chance when looking into plug'n'play temperature monitoring solutions (that are all rather expensive and inflexible) and I'm quite impressed by the work and potential.
Please allow for a rather beginner question if I am on the right track:
Planned:
- Monitor up to 8 different temperatures of my central heating with a sensor in an immersion sleeve
- Monitor up to 8 different room temperatures
- Potentially monitor output of a Combined Heat and Power unit
Selected Hardware:
- 1x Raspberry Pi with a RFM12Pi expansion board
- 1x emonTx 868Mhz kit
- 8x Encapsulated DS18B20 temperature sensor attached to the emonTx on a 1-wire bus
- 1x 100A max clip-on current sensor CT attached to the emonTx
- 8x emonTx Temperature Nodes 868Mhz for the room temperature
Does this make sense or am I on the wrong track?
Additionally can someone point me to the diameter of the encapsulated DS18B20 as my immersion sleeves will max fit 6mm.
Re: Temperature monitoring project
That looks generally OK to me. As the temperatures change only slowly, you shouldn't have a problem with collisions in the radio channel. However, you might want to read up on the temperature sensor to see whether the wiring constraints of the one-wire bus can fit in with your arrangements.
But you're out of luck with the temperature sensor size - the encapsulated one from the shop that I have is a tight 6.5 mm overall diameter. The body itself is exactly 6 mm, there's a heat-shrink sleeve over the back end that supports and waterproofs the cable, and that takes it up to 6.5 mm. Maybe as you don't need it to be sealed, you can use discrete DS18B20s, solder and sleeve the connections yourself? - the sensor IC itself is a TO-92, 5.5 mm diameter.
If you want logging, you may want to add a hard disk drive to your Raspberry Pi.
Re: Temperature monitoring project
Many thanks for this first feedback.
Basically I could create the sensors myself as there are 6mm empty metal sleeves available and together with a heat conductive casting compound it would just work nicely.
But as I am basically lazy, I'd prefer to have them ready made. Is there a chance to just cut the heat-shrink sleeve?
As for the sensor arrangement I am planning a normal mode star arrangement with the most distance sensors below 10 meters.
As for the logging, do you think a regular SD card will fail too early due to wear?
Re: Temperature monitoring project
I don't know about cutting the sleeve off the sensor, I haven't looked! It might be worth buying one to try.
As for the SD card, yes. Logging every 5 s, they seem to last between a couple of weeks and a few months. The done thing is to keep it as read-only for booting the OS, then switch everything - but everything - that involves any writes to a HDD.