Humidity / Temperature Sensor

[TimO]

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:

https://codebender.cc/sketch:67176

[doesel33]

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

[TimO]

@doesel33: You're right, thanks!

[gadu]

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

[daulagari]

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

[TimO]

@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.

[Ivan Z]

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

[TimO]

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

[Magiske]

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

[Ivan Z]

My devices

[GizMoCuz]

I think the comment in the routine

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

Should be

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

(R3)

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

Great sketch!