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Forum Index : Microcontroller and PC projects : I2C Bus Slaves - Who is? GY-21P Temp/Humidity Sensor

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steview_de
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Joined: 02/11/2022
Location: Germany
Posts: 12

Posted: 04:50pm 07 Dec 2022

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Hey folks,
first of all ... i don't know exactly if the search function here is really a help. Please excuse me, if i'm not able to control it.
I searched for different key words (I2C, GY21), but cannot get any result i want to have.

Okay, following problem, after reading the manual.
I added another slave to the I2C bus. A Temperature/Humidity Sensor, called "GP-21P".

I have it in my box from other �C projects.

2 Problems with it:
I don't have the adress and i don't know how to get any data out of it.

So, is there a command to "scan" and show the participants on the I2C bus?
And second: How do i get know wich data i have to read to get temp and/or humidity?

Thanks for help in advance.

"Stevie"

JohnS
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Joined: 18/11/2011
Location: United Kingdom
Posts: 4147

Posted: 05:01pm 07 Dec 2022

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You can aways use such as

site:www.thebackshed.com/forum i2c scanner

site:www.thebackshed.com/forum i2c scan

in duckduckgo

John
Edited 2022-12-08 03:03 by JohnS

twofingers

Guru

Joined: 02/06/2014
Location: Germany
Posts: 1682

Posted: 05:10pm 07 Dec 2022

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Hi Stefan,

please take a look:
https://www.thebackshed.com/forum/ViewTopic.php?PID=176762#176762

Regards
Michael

causality ≠ correlation ≠ coincidence

Pluto
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Joined: 09/06/2017
Location: Finland
Posts: 398

Posted: 05:39pm 07 Dec 2022

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Could be this one. Unfortunately you did not show the other side of the board.

Atmospheric Humidity Temperature Sensor Breakout Barometric Pressure BMP280 SI7021 for Arduino GY-21P By DIY

Found on AliExpress.
Seems to be 2 sensors on the board:
Si7021 humidity sensor I2C address 0x40
BMP280 temp and pressure sensor I2C address 0x76 or 0x77

Try with these and see if you get any response.

steview_de
Newbie

Joined: 02/11/2022
Location: Germany
Posts: 12

Posted: 08:43pm 07 Dec 2022

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@Pluto, you seem fully right.
(Unfortunately the upload is not working at the moment :-/ )

On my output of the code from the link i found 6 adresses.

I use the command: I2C READ &Hxx, 0, 2, RData() (from p. 139 of the manual)

00 => with the "print" command i have only "0" on the "output"
3C => Print RData(0) => 1 / Print RData(1) => 1
40 => with the "print" command i have only "0" on the "output"
50 => Print RData(0) => 255 / Print RData(1) => 255
68 => Print RData(0) => 33 / Print RData(1) => 4
� a bit later: => Print RData(0) => 7 / Print RData(1) => 18
� a bit later: => Print RData(0) => 34 / Print RData(1) => 0
76 => with the "print" command i have only "0" on the "output"

On my bus there are:
- RealtimeClock
- SSD1306 OLED
- GY-21P

"Stevie"
Edited 2022-12-08 06:45 by steview_de

phil99

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Joined: 11/02/2018
Location: Australia
Posts: 2833

Posted: 09:03pm 07 Dec 2022

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This version of the scanner also scans the System I2C

https://www.thebackshed.com/forum/ViewTopic.php?PID=194832#194832#194832
Edited 2022-12-08 07:15 by phil99

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