Wireless communication a few years back was the exclusive playground of RF (radio frequencies). Then it exploded: Nordic, Wifi, Bluetooth, Zigbees… Today there are lots of options available.
Simple RF modules though, are still popular and Synoxo has managed to incredibly shrink them to a few millimeters; while still retaining their cheap factor.
Today we review the $1 Chinese couple boards for the SYN115 Transmitter and SYN480R Receiver. Are they worth it?
RF transmitters and receivers are really tiny chips, and Chinese companies didn’t waste time providing breakout boards for the typical applications. We can therefore find each chip in a ready to use package for hobbyists.
And to be honest it is a great initiative because these chips on papers are truly amazing. They boast:
- Data rate up to 10kbits ASK protocol
- Extreme low power (1.8 to 3.6V)
- 300 to 450Mhz operating range
- ~12.3 mA of current when transmitting data
- ~3 mA standby current
- …All of this in only one chip!
The design chosen by the Chinese is a direct translation of the typical application usage of the datasheet. Both the receiver and transmitter feature 3 pins: voltage in, ground and a data pin.
The pin on the left is meant to be an antenna. Its position is slightly off the 0.1 inch mark from the rest of the pins and therefore you cannot solder on a row of 4 header pins. The antenna must be soldered separately.
It’s a shame they don’t include a “trace antenna” because the design for it is actually included in the datasheet. Some people might view this as a good thing though as it makes the chip smaller and it leaves you the option to make your own design.
Interfacing with an Arduino will require a set of resistor or logic level converter because this chip is NOT 5V tolerant. According to the spreadsheet, 5V is the absolute maximum rating of the chip; and it is good practice to stay away from it if you want to keep your module healthy. Most people use 10k and 20k as they are very common resistors. During these tests I used 51.2k and 100k and these work well too.
As for a library to make it work, RadioHead (the successor of VirtualWire) and its ASK driver is giving good results, although as one of the main feature of RF transmission is to spit raw data over the air, you can try to implement your own protocol over it.
Putting it to the test!
We all know how these 10kbps are theoretical. In practice, I could never have signal between the receiver and transmitter at 10 kbps. This benchmark is done at 3.3V, using a 25cm antenna. The program used is the following:
- Set a button on the Arduino connected to the transmitter; send state over the air.
- Receive state on the receiver, turn a LED on or off.
Some button clicks are not detected, and the only way to improve reliability is to decrease transfer rate. 2400bps is fairly reliable, while 4800bps seems to be the good compromise between speed and reliability. Anything above is unusable. As a low power 3.3V radio frequency, this is not really surprising; but it still is very disappointing.
I can only advise against starting a wireless project with these RF receivers/transmitters. Range and reliability is fairly limited and as a result not very suitable for anything. Low power devices is the playground of Nordics, while faster data rate can be achieved with wifi or bluetooth. Pick these better alternatives.
|The Good||The Bad|