SI7021 Multisensor - first try

[riataman]

@n3ro said:

Big THX,

now i have understand how to use the si7021 :)

Reading works great!

But the sleeping current is very high ~1500uA

If you got this breakout: http://www.aliexpress.com/item/Industrial-High-Precision-Si7021-Humidity-Sensor-with-I2C-Interface-for-Arduino/32340228487.html?ws_ab_test=searchweb201556_1_79_78_77_80,searchweb201644_5,searchweb201560_1 it includes a 3.3v regulator and level shifting so you can actually use the sensor with a 5v arduino but it consumes quite a bit of current (60uA in the ones I got) even when idling.

What I did was desolder the regulator and solder a small wire to bypass it (sorry for potato quality pic).

Then I ordered this breakout for future nodes: http://www.aliexpress.com/item/New-HTU21D-Temperature-and-Humidity-Sensor-Module/1970355069.html?ws_ab_test=searchweb201556_1_79_78_77_80,searchweb201644_5,searchweb201560_1 that one doesn't seem to include any additional circuits (other than the pull up resistor and safety? resistor).

[riataman]

@korttoma said:

Speaking of the Si021, has anyone tried to use 2 Si7021 sensors on the same node?

Since the i2c address is hardcoded I see two ways of doing this:

1. Power the two sensors from gpio pins (instead of connecting them to vcc, connect each to a separate gpio pin), when you want to read one sensor you put one high and the other low. I'm not really sure if this will work at all.

2. Use a soft i2c library like this one: https://github.com/todbot/SoftI2CMaster that way you have two sets of i2c pins. I'm pretty sure this one should work.

[n3ro]

@riataman said:

with a 5v arduino

Hey =)
the operating voltage of this component is 1.9 to 3,6 v. not 5v =)

But the idea to remove the regulator to save a little bit energy is cool. i will try it =)

[riataman]

@n3ro said:

@riataman said:

with a 5v arduino

Hey =)
the operating voltage of this component is 1.9 to 3,6 v. not 5v =)

That's true for the individual SI7021 IC, but in the breakout the regulator steps down the voltage to 5v and additional circuitry does 3.3<->5v level shifting. I have tested that particular breakout with a 5v arduino and it works just fine.

[dakky]

does the sleeping current come down to an acceptable level when removing the regulator? 1500uA is quite much for a battery powered node.

[n3ro]

@dakky said:

1500uA

The sleeping current is ~240uA.

But it's possible to tune it a little bit more.

[dakky]

hmm ok 240uA is better of course, but still far away from

@m26872 said:

Mine sleeps at 11uA.

[n3ro]

@dakky Yes, this is because of the multiple sensors on my board. maybe somebody have more tuning tipps.

[Maciej Kulawik]

@riataman said:

Then I ordered this breakout for future nodes: http://www.aliexpress.com/item/New-HTU21D-Temperature-and-Humidity-Sensor-Module/1970355069.html?ws_ab_test=searchweb201556_1_79_78_77_80,searchweb201644_5,searchweb201560_1 that one doesn't seem to include any additional circuits (other than the pull up resistor and safety? resistor).

Thanks for tip!
Unfortunatelly quite expensive. I bought my Si7021 modules on ali for 2,9$.

And what chip is used on this HTU21D module? Si2071 too?
If not, what library is to be used to communicate?

[GertSanders]

Adafruit have a library for the htu21d which works well with Mysensors