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16  Using Arduino / General Electronics / Re: LED dimming affects sensor data on: November 14, 2012, 07:24:04 am
Hello,

First of all, thank you very much for your very fast answer. majenko asked me to post my schematic but I cannot right now. Currently I'm fighting with getting the basic knowledge of how to do all those things, e.g. creating such a schematic file... smiley-wink What I can do right now is making some images and attache them.

The tip of using ceramic capacitor is what I did already for the sensor. According to the data sheet of the sensor I used a 100 Nanofarads capacitor. The power for the sensor is taken from Ardunio's 5V pin.

Does the images help you to get an idea of what I did? There are four images I took but I have to upload them in three more iterrations as the file sice is too big.

Greez,

dialsc

BTW: Is there a good tool to create such schematic files? One that doesn't kost that much?
17  Using Arduino / General Electronics / LED dimming affects sensor data on: November 14, 2012, 05:21:02 am
Hello,

I've just started playing around with my brand new Arduino Mega 2560 and - after some success - run into a problem I do not understand. Before I explain it I should mention that I'm absolutely new to Arduino, working with micro controllers and electrics in general so no background about volts/watts/amps/... is available, just starting from scratch... smiley-wink I've got a ITDB02-3.2s LCD screen with touch pad connected to my Arduino board without any shield -> first success smiley-wink Then I got a DHT11 temperature/humidity sensor connected, too -> second success. Finally I got the data from the sensor to be shown on the LCD -> third success smiley-wink

Ok, here's my problem. I control the LCD with the UTFT library and figured out that turning the lcd on and off in the code did not work. Searching the net I found a sollution and it also lead me to the idea to control the brightness of the background lights - LEDs - by connecting the LED pin of the screen to an transistor which I control over Arduino's PWM port 8. Running this setup I'm able to dim the LCD's background light. So far so good but I had to figure out that the results of the measurements through the DHT11 sensor are getting affected by the puls (correct term?) I set at the PWM port. An example would be:

  • Having defined an output of 255 on the pin, the sensor reports: Temperature: 24 | Humidity: 34
  • Having defined an output of e.g. 115, the sensor reports: Temperature: 26-27 | Humidity 36-37

I did several test runs so I can confirm that the different setting on the PWM port affects the data comming from the sensor.

Here's my question: What's going on? smiley-wink I have no glue why the settings on the PWM port affects the readings from the sensor. Could somebody please help me figuring out what's happening and how to prevent this? I would be highly thankfull.

Greez,

dialsc
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