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HDC1080: RH reading always RH=0.00%

Prodigy 90 points

Replies: 8

Views: 185

Part Number: HDC1080

Hi Support team.

I am having an issue with the HDC1080 Temp/Hum sensor. I have built 3 PCBS and have tried 2 different parts with the same result

with 3 different software for the Arduino.

I am able to retrieve all the device info and Temperatre as follows :

Measurement Resolution: T=0 (0=14 bit, 1=11 bit) RH=0 (00=14 bit, 01=11 bit, 10=8 bit)
T=28.40C, RH=0.00%
Manufacturer ID=0x5449
Device ID=0x1050

But on both devices I always get RH=0.00%. I have followed the guidelines as follows

Pin 1 = SDA, 4.7K pullup

Pin 2 = GND

Pin 3 = N/C (left floating)

Pin 4 = NC (left floating)

Pin 5 = 3.3V bypased to GND with a .1uF cap

Pin 6 = SCL, 4.7K pullup

Pin 7 (Exposed PAD) soldered to the board but left floating

The only other issues I think it might be is that I am using a SAMD21 (Arduino Bootloader) (Same layout as a Feather M0 Datalogger from Adafruit)

and its a 32 bit device, all references have been to the UNO for Arduino I have seen. I made sure to use no clean flux with my heat gun set below the 260C for ~3 seconds

to melt the solder.

Any insight would be appreciated.

Thanks

mike

  • Dear Mike - 

    you can use 8, 16, 32 or 64 bit MCU/MPU with this device, as long it has I2C on it, which the MCU you are using does have. So this should be no issue, and you have proven that you can communicate with the device, since you are able to get MiD, DiD and Temp. 

    So we really don't recommend using a heat gun with these devices for soldering. The device does have an open cavity with access to the polymer, so its very likely you may have destroyed it. I would recommend getting an HDC1080 or HDC2080 EVM and using the end board (you can snap it off) to connect to and confirm your other hardware/software, then perhaps at the same time, get some of these devices placed with an IR reflow machine. 

    Just to confirm here, you are writing bit 12 (to get both temp and humidity) in Register 0x02 first, waiting about 100mSec, writing 0x00 to the part to start a conversion, then waiting the conversion time and then reading 0x00, then 0x01, correct?

    like this:

     

    BR-

    Josh

  • In reply to Josh Wyatt:

    Hi Josh Thanks for the quick reply.

    I will check the timing issue out when Im back in the office tonight. I have 1 last fresh part for testing(More will be coming in next week)

    I cannot use an IR reflow now because the board is already populated. My rework guy can try using a heat gun from the bottom

    for the new part (as not to heat the RH element, or he said he can try to hand solder with a very tiny tip, there is enough pad exposed.

    I will let you know our results by the morning.

    Also is it critical that the exposed pad is connected on the bottom with solder? Or can we just for testing leave the it floating from the part side, we already have the PCB floated?

    Thanks for your help

    mike

  • In reply to Mike Blankenship:

    Dear Mike - 

    the DAP may/may not be soldered (could be left floating) - key point here is the DAP not be grounded.

    In fact, in the Pin Functions Table on page 3 it looks like we recommend to leave it floating, actually. 

    Also, we mention it on page 19 of the DS, too  ==> 

    Further, here on page 15, we say same. 

    page 18-19 explains why/what the DAP is doing in the system (inside the IC) - please note the graph should allow towards the "faster thermal response" because of the DAP. 

    Hope this gives you confidence. 

    BR-

    Josh

  • In reply to Josh Wyatt:

    Hi Josh,

    Thank you for all your help it works now. We hand soldered without the heat gun and

    left the DAP floating without connecting to the pad. My readings for the temperature

    are within .5C of an Extech RH101 (Its not calibrated, just used as a ball park reference)

    The humidity read ~ 49.33% and Extech read ~40.0%. I will follow the guidelines more closely

    in the 2nd document you sent about using thinner traces and having a dummy trace for the NC

    connections.

    Thanks again!!

    mike

  • In reply to Mike Blankenship:

    Dear Mike - 

    Great! Glad its working - can you do a test for me, because if I understand you correctly, you are reading humidity ~9% high, right? If you have have access to temp only chamber, can you bake this unit at 85C for 18-24 hours or if no chamber, leave heater on for about the same time? (this will raise the temp of part to ~85 to 100C - i have seen it go a little higher, depending on the current source - ) 

    you can read temp and humidity while this is going on if you are interested - the humidity number should be low after heater is on and start approaching 0. 

    then after doing this, then see if this had any impact on the measurement - thanks 

    BR-

    Josh

  • In reply to Josh Wyatt:

    Hi Josh,

    Were off for the 4th of July weekend but I will bring it home and  let it bake in my quasi

    poor mans thermal chamber I use for home projects, it will goto 60C, I modified it a little

    http://www.benchmarkscientific.com/MyTemp.html.

    Ill take readings every second and log them.

    Response time is much better then the DS18B20 sensors we have been using, and the library is much smaller

    Thanks

    mike

  • In reply to Mike Blankenship:

    Mike - 

    Sounds good - Happy Independence Day!!!

    BR-

    Josh

  • In reply to Josh Wyatt:

    Hi Josh,

    Here is some data from the sensor. I had access only to 60C during the holiday. I put all the raw data into a graph, and did a simple chart.

    Does the data look right? At 60C should the humidity stay stable at ~20RH.

    I played around with the Heater for a little bit, when the Heater is on should the Temp be 125C solid? Im not sure

    if it was my tweaked code, but the heater BIT was 1 in the register

    Please disregard the Data dips, I live in Southern CA and we had an Earthquake and the power to my quasi chamber went out for a bit.

    My main system at home was on a UPS so it kept logging data.

    Here is a google link to the data

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