Seeing ~4.8V on 3.3V and VBAT in deep sleep with Photon

I setup an RHT03 temp/hum sensor. I have a program that reads the temperature and then posts it to Then it goes to deep sleep for 1000 seconds. It is powered by 4 Eneloop rechargeable batteries attached to VIN.

It works fine for a while. After a period of time, the wake time seems to be erratic. In some cases, it stops waking completely. I also noticed that the D7 LED is flickering when the Photon is in deep sleep. I measured 3.3V and VBAT with a meter. They are at 4.8V. That’s weird. When the device is awake, I measure 3.3V.

Has anyone seen this behvior with 3.3V supply while in deep sleep?

The max input voltage is 5.5V on VIN. What is the max charged voltage of your 4 eneloop batteries?

Also, I have done a lot of testing with the SMPS of the Photon (and in deep sleep), and it regulates very well to 3.3V in all cases.


Hi @Brad2021hk

Another thing to look at is how is the sensor connected with the Photon in deep sleep: Is it still powered or pulled up? To the 5V (ish) supply or the 3.3V regulator?

If the sensor or pull-up is connected to the 5V supply, that could cause a sneak path back from the sensor output pin to the Photon and raise Vdd via the protection diode in the Photon input. The measured voltage is about right for one diode drop down from a 5.5V supply. You can try disconnecting the sensor from the Photon input while sleeping and see what happens to the 3.3V pin voltage.

Good thought @bko That sensor typically requires a 1k pull up to VDD, but VDD can be 3.3V-6V, so it would be best to power it in this case from the 3V3 pin.

Technically, since it only draws 1.5mA max… it would be BEST to power it from a digital output pin (say D6), and then before you go to deep sleep set the D6 output LOW. Then you don’t even have the sensor’s Quiescent current in the equation.


Thanks guys. I figured it out.

I was soldering female headers to a proto board. The proto board has a ground plane on the top side. You blob some solder between the edge of the top pad and the ground plane to ground the pin. I was not using that feature…on purpose. I guess I had some solder go through on a few of the pins and make very tiny shorts. I was not finding them with my meter. The meter does not auto-range. Most of the shorts were in the 200kohm or more range. I couldn’t see the shorts under magnification because they were under the pin header.

As for the sensor VDD and pull-up, I did have that on 5V. After putting it all back together on a bread board, I did not see the problem with 3.3V or VBAT. I don’t think that was causing an issue. I did decide to go with the recommended design change from BDub and power the sensor from one of the digital output pins. Might as well save the power.

As for the Eneloops, they are NiMH batteries. I’ve seen open-circuit max of 1.3V, so should be safe to use 4.

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Hi Brad2021hk,

I also have the RHT03, but have no idea of how to write code so that it could be posted to Ubidots. Would you care to share your code or inform one on where to get similar code?
Thanks a lot!