honeywell humidity sensor

Goeytex said:

Thanks, I was about to shoot off a note to Honeywell to clarify the ambiguous use of " minimum load" ..

Even then you get an ambiguous answer. Does that then mean that the minimum resistance "could be" 100K ?, Seems to me then that it might be a good idea to buffer the output with a good OPAMP. And the cost goes up even more. These are not cheap and is why I abandoned them.

Might be a better idea to use something like a Silicon labs Si7021 that includes both temperature and humidity with I2C output.

Click to expand...

I read it as "The minimum load resistance is 80K, you could use 100K". Seems on the weak side to me to be driving an A/D input.

The Sensiron SHT series temp/hum sensors are nice parts.

Hi All
Finally got the mag salts and have run a few test
Glad to say the hih4000 is running within its specifications at 75% and 32% at 20 c
to get these results a 100Kohms resistor between signal and OV as indicated in the data sheet from honeywell
I will be using the code supplied by Hippy with it as after looking the results from the standard -42*100/157
Hippys snippit handled the rounding up above 0.5 a little better not my much but a bit more is a bit better than a bit less

Found a nice piece on the comparision of the most used I2c humidity sensors
http://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_many.html
The site looks at the DHT22, AM2302, AM2320, AM2321, SHT71, HTU21D, Si7021, BME280

A big thanks to everybody for there help
Maybe if you have time Eggdweather you could let us how you got on with the BME280 looks
a nice bit of kit adfruit do nicely priced break out board 24bit thou being having a look at afew
code snippits for dealing with 24bits
regards
john

I did not bother using mag salts, wish I had, because within 30-mins of placing the BME280 in a bag of wet Sodium Chloride the device failed, I have a hunch the salt being conductive condensed on the sensor leading to a failure. That said it is reasonably accurate, but as the link you've posted shows the temperature accuracy is average, in-fact from the research I've done all the parameters of temperature, pressure and humidity are within reasonable accuracy limits that make it a good all-rounder.

In my tests I have been able to measure altitude changes at the +/- 0.5cm centimetre level, a simple test of measuring altitude on my bench and then lowering the unit enables me to measure where it is just like using a ruler, quite impressive. I have not had much luck with derived values of altitude as air pressure changes nearly every day.

I have used some of BMP180 code on this forum, but for this device I use an ESP8266 or Arduino because it's so much easier and I use an I2C bus.

I'm sure someone can write the PICAXE code for the BME280 device, but I suspect it will be a challenge.

Hi eggdweather
Found a post on 24 bit where Hippy for the x2 produced this
Having a little look at it and a play the price of the adfruit board at around £6 doesnt seem
so much even if it a failure and a no go
Dark nights need to do something
regards
john

johnlong said:

Found a post on 24 bit where Hippy for the x2 produced this

Click to expand...

Not sure of the context for this comment, but if it is for communicating with a BME280 the datasheet I have looked at says it is has an I2C interface which would probably be the easiest to use.

I use a HT21D, expensive but very easy to use (i2c).

Neil.

Communicating with the BME280 via I2C is straightforward I agree, but there are quite a lot of compensation parameters (28) that are sent from the sensor and then need to be process, a bit like the BMP180 code found on this forum, I think it would be a labour of love to write the code for it using an 8-bit interpreter and integers. Both pressure and temperature values are in 20 bit format, so need a 32 bit signed integer. Humidity is in 16 bit format positive and Bosch recommend it is stored in a 32 bit signed integer.

Using the raw values might be OK, so the compensation values could be ignored.