I am looking to measure multiple temperatures in my attic.
Ambient temp (2x)
HVAC Return temp start (3x)
HVAC Return temp end (3x)
HVAC Distribution box start (3x)
HVAC Distribution junction (3x)
I will use a Pokeys57E as that is a fairly inexpensive device that can expose 1-wire devices over modbus.
For the ambient temperature, I will use a DHT22. I like to have a “neat” installation, so I was thinking about printing a 3D box for it like this.
Questions:
(1) Does the pull-up resistor go at the end of the line (near the DHT22) or does it go near the Pokeys device?
(2) Advice on how to nearly connect this to 22/4 security line? I would prefer screw terminals of some sort, but haven’t found anything in my searching.
For measuring within the HVAC system I am going to use a Waterproof DS18B20.
Questions:
(1) Same as above, where does the pull-up resistor go?
(2) I will need to get power, ground, and then connect data to these. I assume the best way to do that is with a couple of terminal blocks. Does anyone recommend any good terminal blocks?
Onewire is by design a short-distance interface. Modbus is designed for long distance. Careful siting of (maybe multiple?) Pokeys intermediaries could keep onewire cable runs short.
There are direct modbus temp/humidity sensors of course, likely work out more costly but could be used for outlier positions.
Is 30 to 40 feet outside of the 1-wire distance with cat 5 or 22/4? These would be homeruns to the board. I know the 1-wire has issues w/ star topology.
The bosch one does look interesting, but being i2C it would be difficult to place many of those and have a centralized connection point.
Bad news for me on the DHT22… Are you 433mhz sensors battery powered? I don’t like chasing around the house and replacing batteries. I ended up going battery for my locks and I have not been happy with the results.
Yes, but batteries are holding for years and the devices have a battery warning channel, so that’s not much of an issue.
I’m using Oregon Scientific THGR810, but there are a lot of options available…
The modbus 485 temp/humidity sensor is interesting and fairly inexpensive… What would you connect it to on the other end to make the modbus values available over ethernet?
The RS485 sensors need (modest) powering of course, no battery.
Oh, I assumed you had Pokeys gear or something to do this already.
USB-RS485 dongles are dirt cheap to drive a Modbus off your OH host.
You’d probably want one anyway for ease of configuring sensors from a laptop before install.
Thanks.
I access the Pokeys itself using modbus. That is how I can read contact closure and/or one-wire values on any of its 57 inputs. But as far as I know, it doesn’t support reading modbus values itself from another device.
Most of the modbus adapters I have seen (including the one you linked) only support a single modbus device right? I would like something (like the pokeys) that can handle many sensors. I haven’t found anything yet that does that.
Nope. Both the USB adapter and ethernet gateway will drive an RS485 serial bus. That means you can connect somewhere between 32 to 128 modbus devices to the same twisted pair (the exact number depends on the chips and bias resistors in each device)
I guess YMMV. I’ve several of these around the house that have worked and are within the specs in terms of accuracy for years now. I’ve yet to have a failure. But these are indoors in a human habitable area (i.e. temp ranges between 60-80 degrees F and humidity between 20% and 40% (I live in a near desert).
Only think I can recommend (sorry not read all posts) from practical experience:
Buy bunch of 1wire DS18x20 temprature sensors (unless you need humidity, there I don’t have experience). You get them everywhere and they last long time with a lot of abuse .
Use all 3 wires to the DS18x20 1wire sensors if you going long distance (10m+), 2 wire setup is to buggy. Also use good quality cable, I simply use cat5 ethernet cable, lots of cores and don’t break off easily. I also prefer STAR topology, easier to debug.
My current setup is to use a Sonoff basic where I need meassure temperature, connect the DS18x20 sensors and mqtt values out and log onto grafana… But of course you will need to get 220v from somewhere, I simply put plug in my ceiling next to geyser , rest is plugged into wall or wired in as they control some device.
Bit late on this one as only just found it.
I like 1-Wire. A bit long in the tooth but reliable.
The downside is running cable. I use Cat5e for device power and data.
A single cable with nodes at each sensor seems to work well certainly up to 20 or 30 metres.
Each node uses a standard (UK) socket backbox with grid/module RJ45 IDC connectors.
There are also 3.5-mm stereo sockets to inject/take off power
Temperature comes from DS18B20 or 1-Wire devices like DS2438 that have temperature sensing built-in.
DS2438 will accommodate two analogue inputs and another DS (number escapes me) does the same for digital inputs.
I also use Digi XBees for monitoring, good, but not 100% reliable. Much better for serial data, but not so good for digital inputs.
Given the choice would go for hardwired every time and 1-Wire.
A good source of 1-Wire products and applications are Embedded Data Systems (EDS) in US, as are any of the popular development platforms like Arduino
