RDS on an EDM LCD Transmitter

I'd been hearing really good reviews about the EDM LCD transmitter, so I decided to buy one myself. Sure enough, when I connected it to my computer, the audio came out of my car's radio sounding great! So I decided to add the RDS connections.

This transmitter is very small compared to the others, so I knew I didn't have much space to do my modifications. Fortunately, the LCD uses the BH1414 chip, which unlike the BH1415 used in the Ramsey transmitters, has the pilot and MPX signals on separate pins. The pilot signal comes out of the chip at 200mV, which is enough to use as an input to the RDS encoder without a separate amplifier. The circuit to pass the RDS signal from the encoder to the transmitter is simple and uses a 1M resistor to attenuate the signal appropriately.

Parts

These are the parts required for this modification:

An RCA-to-RCA audio cable cut in 2
a 1MΩ resistor
a 1pF capacitor
a 47pF capacitor

Label one end of the audio cable "RDS In" and the other "Pilot Out". Connect the "Pilot Out" cable to the top of R55, (a 56K resistor that is connected to pin 19 of U5. Find a nearby unused ground for the shield. Connect one side of the resistor and both capacitors together. Connect the other side of the 1pF capacitor to ground(pin 4 of the "Option" socket); the other side of the 1MΩ resistor to pin 6 of the "Option" socket; and the other side of the 47pF capacitor to the "RDS In" cable. Connect the shield to ground. This diagram shows the connections:

When connected, it should look something like this:

These cables are small enough to exit the LCD case in the space above the power connector. I fastened them to the power connector with hot glue to provide strain relief.

I used a couple of RCA to BNC adapters to connect these cables to the Pira32 RDS encoder. I adjusted the RDS output level so my radio would receive the RDS signal reliably. When I get the Pira FM Analyzer I'll adjust the level exactly. The good news is that the audio still comes out sounding great!