SI7021 Multisensor - first try

[tbowmo]

@n3ro

It's the way that the libraries are build.. They don't care about how your defines are in your sketch (unless you are on dev branch of the mysensors library.. We are bending arduino build system in that one)

@korttoma

Si7021 has a fixed i2c bus address, so only one can exists on each i2c bus. You could of course use bitbanging to create a second one. But why do you want to have multiple Si7021 on one node?

[korttoma]

@tbowmo said:

But why do you want to have multiple Si7021 on one node?

I was going to use a sensbender node in a location where I would have needed to use an external sensor and instead of attempting to remove the Si7021 from the sensbender I would have just added another (external) one if it was possible. Is there any other temperature sensor that is as good as the Si7021 in battery applications that I could use instead?

[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