BUILDING THE STEPPER (I)

As I commented the other day, the device that receives the pulses from a wallbox and commands the Jukebox is called “stepper”. The steppers were sold as an option, and were connected to the jukebox inside the own jukebox.

The Sinfonola never had this option available. At the very beginning, I tough buying a Rockola stepper like the one above and adapting it to the Sinfonola 2000, however this has many problems like:

-          Rockola and Sinfonola have, for some reason a reverse disposition of numbers and letters in the selector.

-          The Sinfonola has a connection for the contacts in the selector, but it hasn’t the other connector for the control unit

-          I will run the wallbox and the stepper at 50Hz instead the American 60 Hz.

My second option was to build the stepper from scratch using pinball stepper relays (the gottlieb AS relays or the lottery relays). I tried a couple of these (thanks to Jetlagger for lending me these), but they are big, noisy and not very reliable. The third option was to use relays or transistors commanded by a combinational circuit. The change from numbers to letters would be made with a capacitor that cannot discharge trough the train of pulses, but has enough time to get discharged in the gap from numbers to letters. This is the way it was done in the original steppers. However this requires designing an R-C network with no much tolerance. After a couple of tries, I decided to change to a PIC microprocessor that will decode the pulses, translate the selection to a Sinfonola language, and activate the output in the selector.

Finally I will use a PIC16F73, even is many years now that I don’t program in assembler. I also don’t feel very happy using a microprocessor in a 70´s machine, but I will enclose it in a box with an external appearance of an older stepper. I already got a couple of the Rock-Ola/Sinfonola type connectors, called Jones Connectors (Thanks again to Miguel Jetlagger) and I will make it to look like the picture below, with the connectors for the selector (18 pins), one of three pins to the wallbox, and I will need 9 signals from the Control Center.

During the weekend I made some tests with an older 68705 application board (that I can program in BASIC much easier) and in 5 minutes I had decoded the pulses and also figured out how to connect it to the Sinfonola. Now I am sure I will be able to connect wallbox and Jukebox. I will post some photos tomorrow.