MiniRDS Encoder

The MiniRDS

It's not important if you use this RDS encoder with one transistor FM bug or 1 kW transmitter. It will give your station all common RDS features: Program service name, dynamic PS, Radiotext, Program Type identification, Traffic Program, Traffic Announcement and Music/Speech flags, Alternative Frequencies list and some more. This unit is ideal for mounting into a small transmitter.
The design is based on the MRDS192 chip which processes and stores the data and generates output signal. Analogue part is very simple due to fully digital generated RDS signal.

Important note: New improved version has been introduced - the MicroRDS.

  • Small dimensions
  • Very low power consumption
  • Operates stand-alone
  • Unlimited reprogramming
  • Wide control possibilities
  • EEPROM memory for data storage during power-off
  • Broadcast quality output signal
  • Continuous RDS transmission during all operations
  • 4 modes for dynamic/scrolling PS incl. word alignment and one-by-one character scrolling
RDS services directly supported

PS (Program Service), PI (Program Identification), PTY (Program Type), TP (Traffic Program), TA (Traffic Announcement), DI (Decoder Identification), M/S (Music/speech), AF (Alternative Frequencies), RT (Radiotext), User Defined Groups.
(The RDS services are described in Support)

For more information download the MRDS192 datasheet.

Technical specifications
Dimensions: 4.2 x 2.7 cm
Supply voltage: 7-25 V
Supply current: 9 mA
Output RDS signal voltage: adjustable 0-1.2 V p-p
RDS signal bandwidth: +/- 2.4 kHz (43 dBc)
Output impedance: <400 Ohm (DC-100 kHz)
Communication interface: synchronous, IIC based
The unit layout

The unit layout

Supply - Power supply connector
1: + 7-25 V
2: ground

Check the right polarity before connecting the power supply!!!

Out - RDS output
1: output
2: ground

LPT - PC port interface
1: SDA (serial data)
2: SCL (serial clock)
3: ground

Level - Output RDS signal level adjust

How to connect the unit to a PC computer?

For control purposes, the unit can be connected either to LPT or COM port of the PC, each in unidirectional or bidirectional mode. The control software supports all these connections.
In unidirectional mode you will not be able to read any data from the unit back to the PC and you will not be able to detect if the data were sent successfully, but the cable is easier to make. In standard situations any of the following diagrams will work.

  • MiniRDS to LPT port connection cable (unidirectional):

    The 680R resistor may be replaced by a diode as in following case.
    Direct connection between pins SDA and 6 is not recommended.

  • MiniRDS to LPT port connection cable (bidirectional):
        Click to enlarge
  • MiniRDS to COM port connection cable (unidirectional):
        Click to enlarge
  • MiniRDS to COM port connection cable (bidirectional):

    The R9 resistor on the board should be 2k or less in this case (default value is 4k7).

Some important notes:

  • The communication interface meets the IIC serial synchronous bus standard with the clock rate limited to 600 Hz. So the unit can be also controlled from almost any microcontroller.
  • The PC control software emulates the IIC bus on a LPT (parallel) or COM (serial) port.
  • You must be logged under administrator laws in Windows to access parallel port. Serial port can be accessed in all cases.
  • Some low cost USB-to-COM adapters don't handle all port pins required by the unit. You may use Port Access TEST built in the older control application to check it.
  • In some cases bidirectional COM connection may not work if non-standard port is used (USB adapter, laptop PC) - use any other connection.
  • The RDS unit must be powered when sending any data.
  • To store all permanent settings into EEPROM, click on the Store button in the control software. If you forget to do this, your settings will be lost when the power is disconnected.
  • We do not supply any cables or adapters with this unit.

As you can see, cable soldering and some basic electronics knowledges are required. If you prefer complete plug-and-go solution rather, look at the PIRA32.

MiniRDS control software for Windows

Download: TinyRDS_Setup.exe (730 kB) - supports all Windows version from 95 to 8

(Older version:


The software is very simple to use. After install and first opening select appropriate hardware (MRDS192) and connection parameters on Hardware card.

How to connect the unit to a transmitter?

Answer to this question depends on the transmitter you use:

Mono transmitter with audio or MPX input connector (may used with stereo encoder plugged to this input)
Audio/MPX and RDS signal must be mixed together and pluged to the transmitter input. There exist many ways to do this. You may use simple schematics provided below. The resistor values are chosen approximately, but these values might be right.

Mono or stereo transmitter with RDS input connector
It's the simplest situation. Connect the encoder to this input.

Stereo transmitter with audio left and audio right connectors and no more inputs
An encroachment to the transmitter is necassary here. Find a varicap (capacitive diode) in oscillator and connect the RDS input connector by the following diagram. Then fix the connector in front panel of the transmitter.

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