HDC1080: Sample reading and setup

Hi Dharmesh,

Thank you for your post. 

Dharmesh Joshi said:

1. What is the purpose or correct way to use the heater? Is there away on power up to detect the necessity of heater ? Under what circumstance would we need to use it?

The heater is used to drive condensate that builds up over time off of the device. You could apply the heater regularly (say briefly at startup), or use it conditionally if condensation is known to have occurred. 

Dharmesh Joshi said:

2. There is RST bit in the configuration what is the purpose of it?

This triggers a soft reset of the device, restoring it to the default settings. You can also do this by switching the supply, but having a soft reset available is often more convenient.

Dharmesh Joshi said:

3. Once a minute i am reading temperature/humidity sample. Is once sample reading enough, or should i be reading it multiple times within that minute for an average?

As the output is digital data, i though averaging might not be necessary?

That depends largely on your application. You don't need to average to meet the datasheet specifications of the device, so in general I would say not to bother averaging the readings. It may be true that you see smoother "jumps" in the returned data if you choose to average it, but that doesn't necessarily mean the returned data is more accurate. 

Dharmesh Joshi said:

4. Can the size of GND plane or GND pour have any effect on the results. At times two device next to each other would have few degrees for temperature or % for humidity difference. Is this acceptable? If one the PCB is charging a PCB the sensor does show about 5-6 degree extra on that.

It makes sense that your charging PCB would be hotter. When not charging, the difference you are observing is not uncommon. There is likely to be some difference in temperature between two boards even if they are in close proximity to each other. This difference will likely reduce in a chamber, and would be even smaller in an oilbath. When in open air, things like handling the boards, and the presence of air currents can account for these differences. 

Dharmesh Joshi said:

5. I manually soldered the IC using hot air, i then cleaned the board to remove all the flux. Can this effect the readings?

A hot air reflow isn't generally an issue, but no-clean flux should be used for the HDC part. Flux cleaners are likely to affect the humidity readings. You can see our guidance on assembly and handling here: https://e2e.ti.com/support/sensors/f/1023/t/879064.

Dharmesh Joshi said:

I have recently noticed that i was to take my unit from indoors to outdoors, the temperature starts increasing even though the temperature is much lower outside. Can condensation cause such effect?

Condensation could have this effect if it was causing the board to draw more power via a short, but I wouldn't expect it as a rule of thumb. If the device was in direct contact with condensation than the effects would be somewhat unpredictable. If you were recently handling the board and device, body heat could also be the culprit. 

Please let me know if you have any additional questions. 

Best Regards,
Brandon Fisher

Hi Dharmesh,

This thread provides some guidance on how to use the heater of the HDC1080. The max duration would depend on multiple factors for the HDC1080, because the heater only actually runs during conversion. Typically this would be very long.

Dharmesh Joshi said:

RST makes sense now, its purpose is to set it back to the default reg values. I presume if you know the default values then this RST bit would not really be required?  Once the Rst bit is set do you need to release it to stop any further resets from happening?

You don't have to use the soft reset bit ever if you don't want to, and the reset bit will not trigger multiple resets, it will simply return to 0 after the reset is performed.

Dharmesh Joshi said:

The aim is the measure atmosphere temperature/ humidity for agriculture/green houses. Does it make a difference if sensor is on the PCB inside an enclosure or another PCB hanging outside the enclosure?

You typically do not want the PCB with the HDC device sitting entirely exposed, inside a case is better. That case should have some ventilation to allow for exchange of air between the ambient environment and the inside of the case. 

Dharmesh Joshi said:

What is the difference between HDC1080 and HDC 2080? Is there more superior IC to use for my application ?.

I would only use the HDC1080 if you need to operate at 5V, otherwise I would recommend using the HDC2080. The HDC2080 is newer and has better performance. 

Dharmesh Joshi said:

In regards to taking my device in the outdoors i released that my enclosure top is clear, and was causing the temperature to rise, so it was not caused by condensation.

That makes sense, I hadn't considered that as a possibility, but good catch.

Dharmesh Joshi said:

In regards condensation , could it be possible that an issue would arise if during the day time it was hot and during the night temperature were to drop?

Yes, it is possible for condensation to occur due to day/night temperature cycles. You might have to consider designing with the HDC2021, and doing a board conformal coating if you can't reliably prevent condensation in your environment. Conformal coating will protect the rest of your board from moisture

Please let me know if you have any more questions. 

Best Regards,
Brandon Fisher

Dharmesh - 

The HDC2021 is basically the same as the HDC2080 from a pinout and firmware perspective. This device has a removable tape cover and the opening in the device was moved to the center, to allow the tape to adhere to the package. 

The preview product page for the HDC2021 is here: https://www.ti.com/product/HDC2021

and from here on that page you can either request samples (middle of the row) or order some (red button on the left in that row)

https://www.ti.com/product/HDC2021#order-quality

The firmware is not the same as the HDC1080, Please see this FAQ post which covers this topic in detail

https://e2e.ti.com/support/sensors/f/1023/t/878712

The board layout for the HDC1080 will support the HDC20xx devices, as the pins 3 and 4 are no connects for the HDC1080 and the three parts (HDC1080, HDC2080 and HDC2021) have same default I2C address, however, if you have the opportunity to update your board at some point, you could connect pin 4 to interruptible GPIO on your MCU, to take advantage of the DRDY/INT feature the newer parts add. 

Dharmesh - 

I can get someone to look at your account - sure thing - that might take a day or two, since its the weekend. 

In the meantime, so you know - i was able to contact our planning folks, as we do have stock of the HDC2021, and they are moving some parts around to fix that non-stock issue you pointed out. Thanks for pointing that out! 

In the meantime - if you can email me directly at josh.wyatt@ti.com, i can arrange HDC2080 parts to ship directly to you, but I need your shipping address (in case you want them to go to somewhere other than your 38 Clova Road location (in your E2E profile), along with telephone # and your company's VAT #. 

if you can provide that, i will be happy to get those on the way to you.