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Posts: 1
Registered: ‎04-14-2016

Si7020 read data MSB , all bits are always HIGH or LOW

HI,

 

Data is read after sending command 0xE5 "Measure Relative Humidity, Hold Master Mode" 

Data is read after ~ 10 msec. MSB  bits are always high in room temperature.  Now when I head teh sensor, MSB bits becomes low. 

 

For eg: I get 0xFF7A from sensor when the another reference Humidity Meter reads 65% RH.

Now when I heat Si7020 sensor and the reference sensor meter , 7020 returns 0x0052 where as the meter reads 57%.

 

When RH is calculated based on the equation provided in datasheet the sensor data is totally wrong.

 

Please see the attached oscilloscope images.

 

Appreciate any help to debug this.

 

Regards,

Anil

Posts: 59
Registered: ‎04-09-2015

Re: Si7020 read data MSB , all bits are always HIGH or LOW

Thank you for your post. Also thank you for entering this question in our technical support system. I will respond there.

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Super Star</font></font> </a> pcg
Posts: 5
Registered: ‎03-16-2017

Re: Si7020 read data MSB , all bits are always HIGH or LOW

I purchased a SL7020 -A20 IM

I am planning to use this sensor to my IOT sufotware.

But this chip doesn't have any USB support.

How do I hook up this chip to an USB so that I can program the chip?

Posts: 59
Registered: ‎04-09-2015

Re: Si7020 read data MSB , all bits are always HIGH or LOW

The Si7020 does not need programming. It is a simple and standard I2C interface that works on command/response mode. In most systems there is an MCU that does the USB interface and this MCU will generally have an I2C peripheral that will allow you to perform the I2C operations to make a conversion and read the data.

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Super Star</font></font> </a> pcg
Posts: 5
Registered: ‎03-16-2017

Re: Si7020 read data MSB , all bits are always HIGH or LOW

Thanks for the info.

In my IOT software, I need to store a program on the sensor.

So, to write the piece of code, I need access to the chip through an USB.

Is this possible with the chip I purchased?

If not, what chip would you recommend>

Posts: 59
Registered: ‎04-09-2015

Re: Si7020 read data MSB , all bits are always HIGH or LOW

Normally an MCU is used for the USB interface and then the MCU gets data from the sensors. The MCU can be used to store data and programs etc..

 

Silicon labs sells many 8 bit and 32 bit MCU that have USB interface and can communicate with the sensor by I2C. For example the EFM8 "Universal Bee" or the EFM32 "Happy Gecko". Please see our web site form more details about these products.

 

 

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Super Star</font></font> </a> pcg
Posts: 5
Registered: ‎03-16-2017

Re: Si7020 read data MSB , all bits are always HIGH or LOW

My iOT software recommended using Si7020.

Which MCU is based on Si7020 that has an USB interface?

Thanks

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Posts: 2,813
Registered: ‎02-07-2002

Re: Si7020 read data MSB , all bits are always HIGH or LOW

The Si7020 is a sensor, not an MCU. And there is no derivative MCU that has this sensor integrated inside. And there may also not be a demo board with an MCU and this sensor.

 

What is your iOT software that makes this recommendation? On which processor does this software run? What kind of interfaces does this processor or board have?

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Super Star</font></font> </a> pcg
Posts: 5
Registered: ‎03-16-2017

Re: Si7020 read data MSB , all bits are always HIGH or LOW

I am trying to use SAP iOT software.

They mentioned I have to use Si7020. Obviously this looks to be an incorrect info.

I bought this chip which is useless now.

Can you please recommend a suitable MCU that can be programmed and using wifi can

transmit the temperature and humidity to my iOT software?

Posts: 59
Registered: ‎04-09-2015

Re: Si7020 read data MSB , all bits are always HIGH or LOW

There are no MCUs from any company that have the ability to measure humidity and temperature and transmit the data by wifi.

 

You will need at least two chips, one for measuring the temperature and humidity (Si7020) and one to handle WiFi. For WiFI consider a module for easy implementation. We have a few offerings in this area which can be found at

 

http://www.silabs.com/products/wireless/wi-fi

 

 

Posts: 2,813
Registered: ‎02-07-2002

Re: Si7020 read data MSB , all bits are always HIGH or LOW

[ Edited ]

SAP as in www.sap.com I assume then? And this iOT software runs on the SAP controller right?

 

And how did you intend to connect the chip? I have never seen a chip with a USB connector on top. Usually a chip is placed on a PCB. Do you have a PCB under the chip as well? If so, did you make it yourself or buy it as a module?

 

You didn't mention wifi before. But if you want to send the data over wifi, maybe you can use a Raspberry Pi 3. It has an I2C interface as well for connecting to the Si7020. There's even a Linux driver for this sensor.

 

Or maybe you need the Si7013 USB Dongle Evaluation Kit which also contains a Si7020-EB.

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Super Star</font></font> </a> pcg
Posts: 5
Registered: ‎03-16-2017

Re: Si7020 read data MSB , all bits are always HIGH or LOW

SAP iOT software also recommends

 

Tessel 2 which has on-board Wifi capabilities

 

This costs $48.95 on Amazon.

Posts: 59
Registered: ‎04-09-2015

Re: Si7020 read data MSB , all bits are always HIGH or LOW

OK you will need to get the data by I2C transactions. If you do not have I2C available you can consider one of our PWM output sensors like Si7022.