Fader start/stop

Upgrade Kit for Home CD Player

I once heard about the Fader Start: If you pull the fader on the mixer out of the 0 position, the CD player starts to play the selected track. But how to set it up? If you solder the button in the console parallel to the button of the player, it can't be used when the mixer lever is set to 0. So a circuit is needed, which bridges the respective button in the player via an optocoupler on the rising / falling edge of the button pulse and thus triggers the play / pause function.

After two days of work I made this circuit, which works without any problems in my old Denon player:

Picture: Circuit diagram

A 74123 double monoflop (or: one shot circuit) provides the needed short pulse. Both are connected via the reset input in such a way that only one optocoupler can be switched through at a time. The 390K resistors and the film capacitors determine the length of the pulse. The outputs of the optocouplers are connected in parallel to the play / pause button in the player. The controller in the console actuates the button in zero position.

I built the small circuit on an old breadboard.

Picture: Circuit board
Picture: Circuit board

The necessary 5V were already available on the board of my CD player.

Picture: Built in circuit board

The connection to the mixer is made via a socket on the backside.