SI7021 boards

[GertSanders]

@TimO said:

HTU21D

I also like the HTU21D boards, but I prefer the really small SI7021.

I was wondering which other options there are.

I also use a breakout board with power converters on it:

So the question is, are there any other small options ?

[m26872]

@GertSanders Where did you find it?

[GertSanders]

@m26872 I found both SI7021 on Aliexpress.com

[m26872]

@GertSanders Link?

[emc2]

Not SI7021 directly, but there are a lot of small sized I2C sensors.

I use a BME280 board on my gateway and on a node.
I also use a BH1750 (slightly bigger) outside to track plants sun exposure.

If you end up with a design where the I2C bus is included I can definitively see a lot of uses for it!

[AWI]

Another off-topic.. I use these bmp180 boards to power the low power nodes from a 4.1 volt rechargeable Li cell. The LDO is broken out on the connection

[AWI]

@m26872 Industrial High Precision Si7021 Humidity Sensor Module With I2C Interface link

[GertSanders]

Without LDO, but with pull up resistors (smallest board I could find):
http://www.aliexpress.com/item/Industrial-High-Precision-Si7021-Humidity-Sensor-with-I2C-Interface-for-Arduino/32524005324.html

With LDO:
http://www.aliexpress.com/item/Si7021-Industrial-High-Precision-Humidity-Sensor-with-I2C-Interface-for-Arduino/32529522264.html

[m26872]

@GertSanders and @AWI Thanks!

[Carl H]

Your plan is it to change your narrow board with SDL/SDA pad. maybe a jumper to change D2/D3 pin to SDL/SDA?

[gloob]

It`s a mess that the pinout of both modules is different.

[GertSanders]

@Carl-H it's a possibility. No plans yet, other projects ongoing.

[fleinze]

I just received some si7021 boards from china. They are with LDO and level shifter, similar to
http://www.aliexpress.com/item/Si7021-Industrial-High-Precision-Humidity-Sensor-with-I2C-Interface-for-Arduino/32529522264.html
(the original offer went offline, it was from a reseller named "home boutique", no idea why they sold this item)
If I use them with a battery node, is it sufficient to remove (and short-cut) the LDO or do I need to remove the level shifter too?

[AWI]

@fleinze I would suggest to leave these as they are and measure the consumption. Removing the LDO didn't give me a noticeable difference. It could depend on the board however.

[[[global:former-user]]]

@fleinze I am using ATmega328 with 1Mhz and with LDO i have 15uA in standby mode. I have removed the LDO and measured 8uA. You should try it yourself.

[m26872]

@fleinze I wrote a few words about it over here http://forum.mysensors.org/topic/3049/slim-node-si7021-sensor-example/

[fleinze]

@m26872 @kenci @AWI Thank you very much for your answers!
I will go for removing the LDO but letting the level-shifter in place, because it is a pain in the ass to bypass the levelshifter.

Bypassing the desoldered LDO is very easy. Just connect the following point on the resistor-array:

[AWI]

@fleinze The 662k on this board has a typical drop-out of 250mV and power consumption of only 1uA... and takes care of a stable power supply. I doubt if there is any advantage in bridging or removing the LDO.

662k

si7021

[GertSanders]

@AWI What happens when the input voltage drops below 3.1V ? It seems the output voltage just follows the input voltage minus the dropout. I have not measured this yet, but I'm assuming this, since i have nodes working below 3.1V and sending temperature and humidity readings.

[AWI]

@GertSanders No conclusive reading from the datasheet. I will do some measurements later. ..