Sonoff POW R2 and GPIO alternative?

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fires
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Sonoff POW R2 and GPIO alternative?

#1 Post by fires » 09 Oct 2019, 19:24

Hi, I'm unable to find a schematic for the new version of POW (R2). On some sites, I read that is not possible to connect anything on RX and TX ports because they are connected to AC Live wire.. I measure it and had to say it is true. So my question.
I looking for a board to control my floor heating so I need a relay and 10K thermistor input. On sonoff basic, it is simple to use ADS1115 connected by I2C and connect the thermistor to ADS1115. But I looking for some board what is made for bigger current ratings ( like POW R2) just for sure. Also, all terminals on one side are better. Do you have some suggestions?

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Re: Sonoff POW R2 and GPIO alternative?

#2 Post by TD-er » 09 Oct 2019, 22:16

First of all, don't use Sonoff devices because of their stated "bigger current ratings". (maybe also best not to use "Sonoff" and "bigger current ratings" in the same sentence ;) )

Their relais simply are too small for handling higher currents. I would not go beyond 4 or 5 Ampere.
Also their fuses are not really meant for high currents and will get quite hot.


Apart from that, the electronics are not isolated from mains power. Especially the POW ones have for sure a direct connection to mains.
So any sensor you may connect to the electronics will also have a non-isolated connection to mains.
Thus any thermistor you may connect to it will also ... well you get the idea.

As a rule of thumb, any sold device that can also measure current does have a direct connection to mains.
Only exception are the ones using a coil or a Hall effect sensor to detect the current without contact. (I do not know any ESP based device sold off the shelf using contact less measurement of current)

fires
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Re: Sonoff POW R2 and GPIO alternative?

#3 Post by fires » 09 Oct 2019, 22:27

Thanks fo repĺy. I realy do not need current consmption measure.. I just need relay and measure thermistor in floor. So I2C or analog pin..

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Re: Sonoff POW R2 and GPIO alternative?

#4 Post by TD-er » 09 Oct 2019, 23:09

What current should the relay have to handle?

Since your thermistor must be in direct contact with the floor (concrete?), it is best to have it properly isolated from mains power.
It is after all like connecting mains power to ground in a more literal sense :)

You could have a look at low voltage units and let that one switch a bigger relais, or even solid state relais for switching the floor heating.
I don't know any ESP module sold off the shelf with proper isolation, but you could make one from a Wemos D1 mini or NodeMCU and some USB power charger.
To switch a solid state relay you don't need much. Just keep in mind those relais can also get warm so you may need to add a heat sink on a solid state relais.
Also most solid state relais only can switch AC, not DC.

fires
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Re: Sonoff POW R2 and GPIO alternative?

#5 Post by fires » 10 Oct 2019, 08:15

Thanks for reply.. So back to start and I will had to design my own pcb for this :) Thanks for info.

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