Cheap & good boost converter and good temperature sensors

[LastSamurai]

Hey,

I need some advice for new battery powered sensor boards of mine concerning two topics:

• Boost converter: Most sensors don't work well below 3.3V it seems and I am using two batteries (so when they discharge the voltage may drop below that). Do you know and cheap and good (e.g. not drawing too much power) boost converters (to 3.3V)?

• Temperature and Humidity Sensors: I am currently using the DHT11/22 sensors but they aren't the cheapest and it seems like they don't work below 3.3V. Are there any alternatives that are equally (or better) precise and also work with less than 3.3V and perhaps even cheaper?

Thanks!

[MikaelK]

Hello,

For the temperature, the mcp9700 is cheap and works from 2.3v up to 3.1v. The accuracy is not good out of the box (+-2°c) but it can be improved via calibration.
Here's some reading about it : http://blog.kkessler.com/2012/06/20/mcp9700/

Mikael

[LastSamurai]

@Mikael-Kermorgant Thanks! Seems like there is nothing like the DHT for lower voltages, but your sensor seems to be a nice alternative for the temperature part. I guess for the other sensor I have to use boost converters although I'd like to avoid that. They use too much power themselves and they seems to cost more than the sensors themselves.

[MikaelK]

There are a some low voltage temp+hum alternatives, although not cheaper than the DHT.

There's at least the Si7021, which should work between 1.9v and 3.6v

[wergeld]

You could also just use a thermistor (https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=10k+thermistor&tbm=shop). Cheap and not critically dependent on a particular voltage.

[LastSamurai]

Thanks for the help guys. A thermistor can't measure humidity though and while that's not really need I find it interesting to know. I ordered some of the Si7021 and will try them out.

Some of the sensors do need 3.3V or even 5V though. Can you guys recommend any boost converters that work well with battery usage?

[Igor Katkov]

Two AA gives you 3.2V when fresh and decline rapidly

I've read that DH22 gives wrong reading with lower voltages, so to properly power DH22 you need to maintain 3.3V from the day one.
After some research I found these step up regulators

https://www.pololu.com/product/2563

[Igor Katkov]

With regard to 5V periphery I ordered
[1] http://www.aliexpress.com/snapshot/7243167912.html
[2] http://www.aliexpress.com/snapshot/7248371073.html

Both have quite high cut off voltage i.e. they will not boost if voltage drops below certain value, I believe i's like 2.4V :-(
#2 refused to work with my servo motor at all, so I don't recommend it. #1 is sort of OK but you need 3 AA cells to make a good use of it unfortunately.