Raspberry Pi experiment 17: RF 433Mhz with SMAKN Tx/Rx Kit

Goal: Learn using RF 433Mhz with SMAKN Amplitude-Shift-Keying Tx/Rx Kit

Components:

SMAKN 433MHx Transmitter and Receiver modules (ebay) (scarce data is downloadable)

IMG_20150425_081423  IMG_20150425_082118

– RPi and its GPIO pins

– Tool: http://www.zeitnitz.eu/scope_en described also here

Wiring:

rpi_tx_rx_01

SW:

Virtual wire from here by abyz with a bug fixed by me (the tx gpio pi wan’t set to 0 after transmission completion thus a sometimes lots of strong noise was observed at the receiving side).
This utility code uses pigpio module also from abyz

– Code from mine experiment

Conclusions:

– Even bad scope gives eyes when dealing with signals and especially RF
– In case of this SMA RF kit at least one antenna is essential (either at transmitting or receiving side) to improve signal strength (and consequently signal to noise ratio – SNR).
– Receiver has small coiled antenna soldered on it. The antenna we add just extends the default antenna coming with the module. The expanded antenna also amplifies noises. Thus, spoken of signal-to-noise-ratio (SNR) ,  it appears to me to me (based on this experiment) that the best configuration with these modules is: straight-wire antenna  at the Transmitter and default antenna at the Receiver.

Experiment Description:

– this is a constellation with antennas at both sides transmitting and receiving: transmitter – 21sm of straight wire, receiver – 36sm of wire coiled into 3.5sm long antenna
IMG_20150423_094704 IMG_20150424_150458 IMG_20150424_213919

– DATA pin sensed at the receiver
IMG_20150424_212410IMG_20150424_212955

– DATA pin sensed at sender. I’ll never sense this pin anymore at this experiment. At all the antenna constellations I sent the same data and the signal is always clear and strong as it is sensed before modulation and distortion in radio.
IMG_20150424_212745 IMG_20150424_212810

– this how noise looks at the receiver side when data pin is forgotten to be cleared to 0 at the sending side
IMG_20150425_063859 IMG_20150425_064123 IMG_20150425_064127

– this time antenna at the receiving side was expanded to 72sm of coiled wire forming 7sm antenna; transmitter still having an antenna of 21sm of straight wire

the noise:
IMG_20150425_073318

the data:
IMG_20150425_073609

the antenna at the receiver:
IMG_20150425_074447

 

–  this time sending side has no antenna, while receiving has 7sm of coiled wire
IMG_20150425_075415 IMG_20150425_080332 IMG_20150425_080357

– here the receiver has no antenna while sender’s antenna is 21sm of straight wire
the noise at the receiver:
IMG_20150425_074500

the data at the resiver:
IMG_20150425_074615

the antenna at the sender:
IMG_20150425_075330

– now how it looks without antennas at all. Data signal at both pictures looks much more distorted and having lower amplitude. In both the case the data packed was not received at the end, while it was received with configurations having some antenna at least at one side
IMG_20150425_080506 IMG_20150425_080523 IMG_20150425_080726

 

Related Links:

–  How to control power outlets using RPi/Wireless power outlets

Wireless RF links and noise reduction tutorial

pigpio Python module

GPIO virtual wire

Adding 433 to your RPi

 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s