Although restricted to just a few tens of milliwatts transmit power, the licence-free 433.92MHz (“433”) ISM (Industrial, Scientific and Medical) UHF band has continuing appeal for both professionals and hobbyists.
Originally reserved for non-commercial radio use, considerable innovative data handling has emerged in recent times, with the low data rates (~9600bps) especially tempting for easy microcontroller wireless applications.
Of course, 2.4GHz Bluetooth, WiFi and ZigBee wireless gear now abounds but these technologies best suit only very close links, as the higher radio frequencies are blocked by almost anything in the way.
In crowded Asian cities, low-data-speed 433MHz devices are preferred for utility reading, as lower UHF frequencies have better “punch” through obstructions.
Although surprising performers for what they are, most cheap 433MHz data modules are generally very low powered (a mere few milliwatts) and often the receiver is somewhat “deaf”.
Jaycar’s venerable ZW3100 and ZW3102 ASK (Amplitude Shift Keying) AM pair are typical, with their continued popularity relating to ease of use and simple set-ups.
Superior FSK (Frequency Shift Keying) FM types are usually less susceptible to interference, although bandwidth will be greater. Enhanced performance however comes with GFSK (Gaussian Frequency Shift Keying) modulation, as the outgoing data is shaped to a narrow bandwidth, thereby improving receiver sensitivity.
The module really is small, as shown here (with a stamp for comparison!). At right is the connection data.
Australian PICAXE agents Microzed now handle a range of Chinese-made Dorji 433MHz GFSK modules and adapters. There’s even an innovative DRF5150S wireless sensor transmitter (and matching DRF4432S receiver) that can directly read such industry standard sensors as the Maxim DS18B20. That’s right – no external micro needed!
Module prices are around $25 each.
The circuit is very similar to earlier PICAXE 433MHz modules - the biggest difference is that we haven’t had a moment’s difficulty getting the Dorji to work!
Several Dorji transmitters however have powers that exceed the 10dBm (10mW) or 13dBm (25mW) 433MHz limit legally permitted in most Western countries.
The stamp-sized (OK, large stamp!) DRF7020D13-043A transceiver appeals for its features and legal transmitter and it’s this that the article focuses on.
The “7020D13” (so called for its RF IC) is powerful (20mW), sensitive (around -118dBi at low data rates), versatile and easy to use.
Inbuilt buffers and error correction give reliable “wireless serial port” action – essentially what’s sent out at the TX (transmitter) of one module is transparently seen at the RX (receiver) of the other. The modules handle all the hard work!
A rugged gold plated SMA antenna socket is also featured, so you can connect the antenna of your choice. More on this shortly.
They are indeed a little power house!
Leading-edge 433MHz offerings of just a few years back, although considered smart at the time, increasingly look quite tame in comparison.
Dorji modules – the name arises from a Tibetan word meaning “a reliable and trustworthy guardian of peace and justice” – are noticeably similar to other Chinese models.
Close inspection reveals a common use of the high-performance Analog Devices ADF-7020-BCPZ transceiver IC (www.analog.com/en/rfif-components/rfif-transceivers/adf7020-1/products/product.html), although a “1BCPZ” was noted on the Dorji.
Controlling micros may also differ; for example Atmel on one versus “0C002” on the Dorji.
As they have a different on-board microcontroller and RF IC hardware, the likes of Appcon’s “RF Magic” configuration software probably won’t work with the Dorji transceivers.