James Adams

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• Zen Remote

Background

In early 2006 the CD player in my Dad’s car started chewing up CDs, unsuprisingly we quickly replaced it. Examining the remains, I came up with the idea of re-using the control panel and interfacing it with my (rarely used) mp3 player, an old Nomad Jukeboz Zen. I considered soldering leads onto each of the Zen’s buttons but access to the PCB is somewhat tricky.

Several months later, having sucessfully wired up an aux socket to the old head unit by cutting into the tape pre-amp, I once again toy with the idea of using the CD player control panel to control the MP3 player. Noticing the socket for the wired remote, I begin searching the web for any details I can find on the remote interface. Hours of scouring various forums later and much trial, poking and error, I have a rough idea of how it works.

Connector

Pin 1

Ground

Pin 2

Function Control

Pin 3

Serial Data (TTL) and line in

Pin 4

3.3V Power Supply

I have used a small piece of stripboard as a plug but other people have reported sucess using the wafer from a USB plug with the casing removed.

Pin 2 is rather interesting, instead of a serial data interface to issue control commands, it uses a system of resistances to represent which command is being issued, this has the advantage of being rather robust and extremely low-cost. As it turns out, Sony’s mini disc player remotes use a very similar system.

Resistances

Opinions seemed to vary wildly about what reistances across pins 1 and 2 actually did what, so armed with a large potentiometer I set about establishing what actually did what. The system I came up with is as follows.

• A 1M resistor across 1 and 2 informs the player that a wired remote is connected. * this is confirmed by a data burst on pin 3 and the power supply to pin 4 being activated.

• Dropping the resistance by means of other resistors connected in parallel indicates different functions, as shown below.

Additional functions are available by holding down the following buttons.

Play/Pause

Powers on the unit

Next

Seeks forward

Prev

Seeks backward

Stop

Powers off the unit

EAX

Switches to recording mode

When in recording mode, a microphone connected across pins 1 and 3 (data and ground) can be used to record voice input, however data is still transferred while recording, so the microphone should probably be protected from the data bursts by some means.

The prototype has now been installed in the car and is fully working, complete with power supply, something I overlooked though was the drop in voltage during ignition, the Zen refuses to use it’s internal battery to compensate for this, resulting in the player locking up and needing a hard reset. This could be fixed with an UPS battery and a diode or perhaps a super-capacitor.