Construct a wireless temperature sensor

This product is being replaced by our improved 2nd generation wireless temperature sensor
Project Description

This project assumes you already have a Model A or B Raspberry Pi, power supply, HD card, screen, keyboard, network etc. Raspbian Wheezy OS.

In this project you will construct a wireless battery operated temperature sensor. The sensor communicates with the Raspberry Pi over radio frequency (RF) communications to a base station RF receiver. You can connect as many transmitters as you like (e.g. inside, outside, fridge, etc…). 

What you need

The parts can be purchased from the PrivateEyePi Store

  • 1 or many Wireless Temperature Sensor (RF02), which includes a 10K Precision Thermistor and a 10k resistor
  • 1 x Wireless Sensor Case Kit (RF04), shown on the right. This is a really nice kit that contains the PCB, coin cell battery battery and casing and plug-in slot for the temperature sensor.
Optional:
  • If you choose not to use the wireless sensor kit then you may want to consider using a 2mm 10 pin header to plug (RF08) into the RF sensors in order to avoid having to solder wires directly to the RF sensors. You will also need a 3V power source, like 2 AA batteries.

How it works

The wireless temperature sensor will transmit the temperature at 5 minute intervals to the base station. The transmitter is optimized for extremely low current consumption so that it is able to last over a year on a single set of batteries, or 1 coin cell if you are using the wireless sensor kit (RF04).   The RF units are very powerful and should easily handle communications distances around a residential home. The antennae of the transmitter can be adjusted for longer distances, or for greater strength to compensation for walls or other physical barriers. The transmitters come pre-configured with a unique number identifier that will be used to uniquely identify each sensor. This enables you to have as many wireless temperature sensors as you want (e.g. inside, outside, fridge etc… ). The Python code required to read the temperatures from the serial communications stream is provided. We also provide the code to send the temperature value to the PrivateEyePi server to be displayed on your WWW dashboard; however this is not a mandatory part of this project. If you want a wireless temperature sensor for other projects then these steps will help you achieve that goal too.

Construction

Follow the following build guide for the wireless sensor kit (RF04) and plug the RF transmitter as shown in Figure 1. 

The RF transmitter looks exactly the same as the receiver units so be careful not to mix them up. The packaging of the receivers and transmitters will be clearly marked so you know what is what. If you do mix them up them some trial and error testing should solve the problem.

The two white wires you see protruding on the right hand side are connected to the thermistor temperature sensor. 


Figure 1 - A wireless sensor case kit with a temperature sensor attached

Alternatively you can choose to connect the thermistor directly to the coin cell board  as shown in Figure 2.


Figure 2 - Thermistor connected directly to the coin cell board

That's it! Now you are ready to move on to the software section.

If you chose not to use the wireless sensor case kit you could construct the wireless sensor using your own circuitry. The tricky part is connecting wires to the pins of the RF unit as they are spaced very close together and do not plug into a breadboard. You could:
  • Solder wires directly to the receiver unit pins, or
  • Solder wires to a 2mm 10 way header(RF08) that plugs into the RF unit. This prevents you from having to solder directly to the RF transmitter.
Figure 3 shown the circuit diagram and figure 4 shows you the pin numbers on the RF transmitter.


Figure 3 - Wireless Temperature Sensor


Figure 4 - Pin-outs for the RF Modules




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