Issues with DHT11 Sensor

Other Hardware General Electronics
1

Hello everyone,

I'm having issues with DHT11 sensors. Basically, I have an Arduino powered sensor setup which uses BMP180 for temperature and barometric pressure readings, and a DHT11 for humidity readings. It then transmits the data to a receiver using a 434 Transmitter. When I was originally putting things together, I was using an UNO board powered by USB cable from my computer. Everything was working fine with the transmitter and receiver, and all sensors were working as well.

Taking it further, I wanted to replace the UNO board, using the ATMega328 with a voltage regulator, all powered by a 9V battery. When I power it up, everything works fine except the DHT11. It appears to me that there is a problem with the power being supplied to it.

I used this as a reference for building the Arduino on the breadboard: https://www.arduino.cc/en/Main/Standalone. All components used in making the Arduino on the breadboard are exactly as described in this link. I then added the rest of my components and sensors. I've checked all connections to ensure I haven't missed anything, and everything appears to be correct. I have been poking about with my multimeter as well to check for proper input voltage, checking the raw voltage from my battery as well as voltage after the 7805 regulator - all come back fine. I have swapped 7805's as well as tried a AC adapter with 12VDC output as raw voltage. I have also used different 9V batteries as well.

For DHT11 sensors, I have one that is just the module with 4 pins, as well the ones mounted on a board with 3 pins and LED, both of which I have used successfully, powering it from the USB with the UNO board. However, the module with the LED shows the LED as blinking - this being the only visible indication that something is wrong. When powered from the UNO board with USB it is solid. Hence it must be something up with the supply voltage to it, perhaps fluctuation and I am unable to see it on my meter. As a test, I was getting 4.9V supplied using the 9V batter setup, the UNO board itself with USB was only supplying 4.7V - both within specs for the DHT11.

I'm hoping someone may have some insight on a solution for this problem. In the end I'm hoping to solder this stuff together and put in a small box that can be placed outside my house. With the receiver inside with LCD display. I'm attaching a .JPG of a Fritzing schematic that is an exact replica of what I have physically built on a breadboard. Everything works on 5V, except the BMP180, which I used a voltage divider to get the 3.3 for its VIN.

Any help would be greatly appreciated!
Thanks!

Transmitter.JPG
Transmitter.JPG1372×511 119 KB

2

The DHT11 is terribly inaccurate. Throw it away and replace the BMP280 with a BME280 to also get humidity.

3

However, the module with the LED shows the LED as blinking - this being the only visible indication that something is wrong.

Check the schematic for that module...
I think the LED is simply connected to +5v and GND (with resistor) in which case there is definitely something wrong with your supply to it.

Could be bad connection on the dev. board (some have gaps in the powerline tracks).

Does it still flash if you remove the wire to the ATmega ?
(i.e. is it getting just enough power from the pin to light the LED?)

Put an led +resistor across +5v/GND at the module... does that flash as well ?

Yours,
TonyWilk

4

Hi,

I have also used different 9V batteries as well.

What sort of 9V batteries?

Have you measured the input volts and output volts of the 5V regulator?

Has your protoboard got continuous power lines down the side of the board?
Some protoboards split the supply rails half way down the board.

Tom... :slight_smile:

5

Isn't that 10k pullup a little weak? Try a 5k6 or 4k7.

6

Just wanted to say thank you for the replies. I did end up figuring it out finally. It seems to be the breadboard itself. I daisy chained a second board with the DHT sensor on it, and it worked perfectly. It seems as though the contacts on that particular spot of this breadboard were a little touchy. For sake of argument I tried the sensor with the pullup, as well as the KY-015 module and both worked perfectly.

Yes, I did probe around with my multimeter to verify I had the correct voltages appearing in the correct places. Whether or not it makes a difference, a few of my breadboards were cheapies from China. I know I've had similar headaches with some components that I cheaped out on from China as well! :slight_smile:

Anyway, thanks again, I always appreciate a fresh set of eyes on things like this.