Humidity / Temperature Sensor

  • Hero Member

    I've build a sensor to measure humidity and temperature in my living room. It is now working for about 7 weeks.

    The sensor consists of the following components:

    • DHT22 Hum/Temp Sensor
    • MCP 1702 LDO Regulator (3.3V)
    • Atmega328P-PU PDIP-28
    • holder for batteries (4 x AAA)
    • NRF24L01+



    Here are the schematics:


    And here is a screenshot from my OpenHab-View:


    (I'm logging the last update to ensure the sensor is still alive)

    The DHT22 needs at least 3 V to operate stable, so I thought about using a booster or a regulator and took the regulator.

    Currently I'm using rechargeable AAA, which will be switched soon, as the sensor is working fine. The Voltage has dropped 0,1 V (from 5.3V to 5.2V) in 7 weeks and the AAAs were only precharged. My multimeter is able to measure the current, but in case of this sensor it is to low, I need a better multimeter.

    The Atmega328p is running with 8 MHz internal clock and brown out detection is disabled.

    Finally the sketch:

  • A little mistake in your schematic: R2 must be 4,7k!

  • Hero Member

    @doesel33: You're right, thanks!

  • Cool!
    Perhaps a noob question, but how do you program the Atmega?

  • Hero Member

    Currently I'm using rechargeable AAA, which will be switched soon, as the sensor is working fine.

    Why would you switch the batteries?

    5.2V / 4 = 1,3V so still quite full.

    These batteries are low-leakage batteries so provided the initial charge is fine and current consumption the lifespan should be good and at least 50% of that of good alkaline batteries

  • Hero Member

    @gadu I'm using a MySmartUSB MK3.

    @daulagari I'm using rechargeable ones as long as I'm not sure how good my device is working.

  • Hardware Contributor

    I power DHT22 from arduino pin. It help make economy battery. When controller sleep, power pin set to low.

    If using 3.3 power - no needed R2

    If you use CR123A accomulator. You will not need Regulator and the device will be smaller

  • Hero Member

    Does the DHT22 work with 3v? I thought it needs at least 3.3v. I will test that!

  • Can't remember the specs. "Normally" 3.3v is something like 3.0-3.6v..
    Just did the google thingy.. 3v-5v:)

  • Hardware Contributor



    My devices

  • I think the comment in the routine

    void measureBattery() {
    // R1 = 1MOhm, R2 = 220 kOhm

    Should be

    void measureBattery() {
    // R3 = 1MOhm, R2 = 220 kOhm


    Is it possible to add (comment out) some lines how to calculate the battery percentage and send this via gw.sendBatteryLevel (batteryPcnt)

    Great sketch!


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