DHT11 (or other DHT) in a final product?

Hi

With my Arduino project being a success and a couple of friends asking me if they can have the circuit too, I have decided to have 50 PCB's manufactured of my circuit, however I am currently evaluating which components in my circuit should be replaced for the final version. The PCB will consist of only the needed parts of the Arduino (not much) and everything else will be scrapped (usb charging, extra pins etc).

I considered using a DHT11 for my final product however the high price in the UK means that it would be illogical, I have looked on Alibaba and I have found clones (I presume) for around 50 pence. I would rather use components from a reputable source, however I am not completely opposed to using the DHT11 from Alibaba. With regards to replacing it, I could easily measure temperature with a thermistor, however the difficulty comes when finding a humidity sensor replacement. I have not seen any for under 1 pound each (50 quantity) that have been used on an Arduino (successfully).

So does anybody know of any cheap humidity sensors that work well with the Arduino (with reasonable accuracy) and are there any reasons other than price, not to use the DHT11 in my final circuit?

Thanks in advance

The DHT11 is a poor quality sensor , both temp and humiditywise , in that its not very accurate. Whats the purpose of the project?

The purpose is to identify whether the temperature and humidity of a room is acceptable for a baby. It will measure whether the temperature is in a 5 degree range and whether the humidity is within a 15% range.

bexx123: The purpose is to identify whether the temperature and humidity of a room is acceptable for a baby. It will measure whether the temperature is in a 5 degree range and whether the humidity is within a 15% range.

Maybe DHT22?

Okay, so I have looked into the DHT22 which meets my purpose however the cost in the UK is just to high, so one again I would be looking at buying them from Alibaba. I am sure it would be fine, I would just rather buy from a large reputable company eg Farnell.

I have found this humidity sensor - http://uk.farnell.com/multicomp/hcz-d5-a/sensor-humidity-20-90-rh--5/dp/1891428 - and I was wondering how I would connect it to the Arduino as it only has two legs as opposed to the three that you use on a DHT sensor.

That sensor you found is a resistive sensor. That is the kind of sensor that is used inside the DHT11.

I have a DTH11 that was already very bad, but now it is stuck between 30 and 31%RH. The temperature is still working and the checksum is okay. The DHT22 is a little better.

If you really want something cheap, use the DHT22. But don’t expect the humidity to be anything near the actual humidity. They are 2.30 english pounds on Ebay.co.uk

With regards to the circuit for a two leg humidity sensor, would I just use the same as for a LDR or Thermistor? I only need the humidity aspect of the DHT22 so what about this sensor instead? http://uk.farnell.com/multicomp/hcz-h8-b/sensor-humidity-20-90-rh--3/dp/1891429 It is accurate to +/-3% as opposed to the +/-5% of the sensor mentioned earlier.

That one seems even cheaper than the other one. They are used just like an LDR or thermistor.

Are they 23k to 42k for 20% to 90% RH ? You might have to do some averaging in the Arduino for a smooth result. I don't believe the +/-3%, they need to be calibrated, and chemicals in the air can influence it. They don't come with temperature sensor included, so you might have to add a temperature sensor.

It is easier to use the DHT22 and accept that it can be very inaccurate.

I am looking at having it manufactured in a quantity of around 500, so will the calibration have to be done manually for each board? Or is it software based?

Here is my final sensor suggestion, what about this one - http://www.farnell.com/datasheets/1699557.pdf - I am not sure if it is actually a humidity sensor even though it is in the humidity sensor section, however if it is it states an accuracy of +/- 1.5%.

That is a pressure sensor.

When you want to make 500, you have to test and develop it first.
Could you buy a few of those resistive humidity sensors, perhaps also a capacitive humidity sensor, and the DHt22, and also a good sensor, like the Honeywell HIH6000 series.

When I put my DHT22 outside the window, I get a number something like 50%. But when I check wheater stations in my neighberhood, it should be 65%. My DHT11 still has 31%. I have not tested the HIH6000 series myself yet.