1-Wire sensors

Hi. I am planning to install some temperature sensors around my house using a 1-wire bus.

I have found some combined temperature and humidity sensors called DHT11, but I can't find out if they are using 1-wire or not. I would like to use 1-wire in order to be able to daisy chain the sensors instead of using a star network.

The question is if this is possible with DHT11 sensors, or if I should do without the humidity sensor and just buy DS18B20 sensors instead.

Are there alternatively any cheap 1-wire humidity sensors or combined 1-wire sensors available?

You'll need a bunch of digital pins and cables, unless the many sensors are individually adressable. The DS18B20 sensors can be programmed for unique addresses, so that a single data line is sufficient.


Silly answer - does it say 1-Wire on it? No. Have a look at Maxim's site for the full list of 1-Wire devices.

I have just set up a few DS18B20's on CAT5e cable together with humidity.
The ususal route for humidity on 1-Wire is to use something like the Honeywell HIH-4000 series (you will need to check specific numbers, some are 2.54-mm pin spacing others 1.25-mm) with analogue output. Next get a DS2438 analogue to digital IC - be prepared for some fiddly soldering as it's a SOIC or similar.

Now the difficult bit. You will need to write some code specifically for this chip. Have a look at Joe Betchers site for a 2438 library or try Embedded Data Systems in USA. EDS do some nice totally 1-Wire gear and publish some very useful code to get you started - there is a little translation from their stuff to Arduino but it's nothing more than changing some reads and writes. Be nice to the last (first) reference as the EDS folk are really helpful and we don't want them clamming up. The end result, and I'm no hot-shot on 1-Wire or Arduino, is that DS2438 gives you temperature, humidity, the supply voltage, the analogue voltage and some memory for storing set-ups. I don't know if your proposed IC is analogue or some serial output, but I would go for the DS/Honeywell.

I have installed DS 18B20's in the roof space, DS2413's for metering, and DS2438 for ventilation control. The hardest bit was pulling all the cable through. Given the opportunity with a new-build house, I would 1-Wire the whole lot, endless possibilities.

Just a typo

Be nice to the last (first) reference

should have read "Be nice to the last (and first) reference"

A bit more info - I get the 2438's from RS in UK (£5 or less) and the Honeywells from Farnell (£14). I'm only guessing, but if the DH?? device is analogue, then you might need two 2438's - if it's serial, it could be tricky to integrate with 1-Wire

DHT11s are not accurate, I had 5 of them hooked up on a single breadboard and the temperatures they were showing varied from 72 to 77, the RH readings were worse, from 28 to 52.
DHT22 may be better ?? but you can't go wrong with DS18B20s.