This product and tutorial has been replaced, please go here
In this project I will show you how to build a wireless temperature and humidity sensor. The sensor transmits the temperature and humidity over RF to the Wireless Base Station Receiver. This sensor will work seamlessly with the PrivateEyePi system, or you can use it for your own purposes. The temperature and humidity signals, that are received by the wireless base station receiver, are sent over the serial interface in clear text so it is very easy to write you own code to receive the data. We supply a sample Python program that show you how to read the data from the serial interface.
The parts are available from our store in a kit. Note that these are only the parts below and and not include the RF receiver (Wireless Base Station Receiver).
1. 9V battery connector. We have chosen to power the sensor using a 9V battery which is converted to a regulated and constant 3.3V by the power POD (no. 9 in the part list). Both the DHT22 sensor (no. 2) and the RF Transmitter (no. 11) need 3.3V.
2. DHT22 Temperature and Humidity Sensor
3. Developer Board - Dimensions are 3.13' x 2.40' x 0.06' or 79.5mm x 61mm x 1.6mm. A very versatile project board. It has plenty of room for electronic parts that can be soldered in the prototyping area which has horizontally connected rows of pads similar to a bread board. The top left hand section is specially designed to connect RF modules (no.11) or any other RF module that has an XBee footprint.
4. 0.1uf Capacitor.
5. 2 x 10 way 2mm sockets that connect the RF module to the developer board.
6. 6 pin FTDI style header to perform program uploads via a serial interface (not required for this project, but very useful if you want to get into some of your own sensor programming).
7. 3 resistors (10k, 100k and 1M).
8. Jumper wire use to connect various parts on the develop board.
9. Power POD capable of taking a 4.4v to 16v input to give a 3.3v regulated output. It's often used to power 3.3v devices from 4 AA batteries, 6 to 12v PSU's etc. We've chosen to use a 9V battery to power this sensor but you can use any power supply that is between 4.4V and 16V.
Another option for power is to power the sensor with a single AA battery. This needs a different power POD (NCP1402) and a couple battery clips that can be soldered onto the developer board.
Battery life expectancy:
The sensor uses 30.5mA every 5 minutes and sleeps in between transmissions (using .005mA while sleeping). A transmission takes 1 second so you can expect the following battery life:
9V (0.5 Ah) - 288 Days (0.56 Year)
AA (2 Ah) - 819 Days (2.25 years)
10. Two 10 pin connector for the RF module.
11. The RF Module that interfaces with the DHT22 sensor and transmits the temperature and humidity.
Figure 1 - Wireless Temperature and Humidity Sensor Parts List
Soldering the RF module directly to the board requires a technique. I find it easiest to put a small amount of solder on each of the 20 pads (labelled by the two orange arrows in Figure 2), before placing the RF module on the board. The orange arrows in Figure 2 show the 20 connections that need to be soldered (10 on each side of the RF module). Take your time doing this step and be very meticulous about making sure the module is positioned perfectly to the board. If you make mistakes now it will be a lot of work later to diagnose and correct mistakes.
Figure 2 - Soldering the RF module directly to the develop board
Next use jumper wire to connect pin 1 on the DHT22 to pin 15 of the RFu-328 and pin 4 of the DHT22 to GND as shown in Figure 6 & 7.