Temp/Humidity Sensor Not working when on battery

I have the Seeeduino Stalker v2.1 and the SEN51035P Temperature/Humidity sensor. I load up the code from the wiki: seeedstudio.com/wiki/Grove_- … Sensor_Pro

The code compiles fine and works fine when connected to the computer. But when the stalker is running on Li ion battery and removed from the computer, this function does not print the temperature/humidity values to the sensor.

I think one of the two dht11 conditions are not met, and so, no output comes out. As soon as I connect the stalker to the computer through the USB, it is able to write onto the SD card.

My Li ion battery is fully charged, so it cannot be an issue with the battery. Also, other sensors (Grove Hall sensor works just fine when running on Li ion battery) Can you please help here.

Further debug showed that the battery was fully charged and showing 4V. When I connect the stalker to the computer through USB, the USB5V showed a voltage of 4.6V. But when I disconnect from the computer, the USB5V showed a voltage of 2.5V. So, clearly for some reason, the battery when supplying voltage to USB5V is not supplying full voltage to the sensor and hence it is not working.

Please explain how the battery voltage comes to the USB5V?

Please help here, because I need to finish my application fast.

If you disconnect FTDI (UartSBee?) the USB5V pin must be 0V (diode protected!). edit maybe the FET is the problem.
seeedstudio.com/wiki/images/ … ematic.png

Use the sensor with 3.3V pin. It works :wink:

DHT11 library: arduino.cc/playground/Main/DHT11Lib

Thanks for your reply Rony. Thanks for pointing me to the schematics and the FET. I thought that the USB5V is the Vcc and the source of power supply for the other shields. It seems that the 2.5V I saw on the USB must be the capacitive coupling from the gate FET. That would probably explain the 2.5V.

I have not spent time with the schematics, and pins lay-out, so would appreciate if someone could point out the pin-out on the Stalker board which supplies Vcc to the other shields. I don’t want to use the 3.3V for the temperature/humidity sensor, but would rather like if I could hook the Groove shield (and its array of sensors to the main Vcc power supply/battery…)

Appreciate the help that anyone can provide. Also, if someone could explain the root-cause for seeing this problem with the temp/humidity sensor? The other sensors on board work just fine, but not the temp/humidity DHT22 sensor. Thanks again.

I tried putting the DHT22 through a Groove base shield. Again, the same problem. Works when connected through the uartSBee to computer. But as soon as I remove the UartSBee, the temperature and humidity values are not seen. Can some-one from the Seeedstudio team please help?