Reading in impulses of 250 kilocycles current

I have a 1940s Seeburg Jukebox (W6-L56) that I'm trying to connect to an Arduino running an mp3 shield. The manual for the jukebox (link) says that the rotating switch blade inside creates a set of evenly spaced selection impulses of 250 kilocycles current.

The output of the oscillator is connected to the AC line, which suggests to me there's some sort of PWM going on, though I can't fully tell. How does one go about reading in the input on the AC line using an Arduino? I would really not want to fork over money for an oscilloscope.

Thank you in advance!

It's a little confusing because first it says it generates 25 impulses and then it says the number of impulses determines the selection... I may have missed it, but I didn't see the timing between the impulses.

It's not PWM, it's just a pulse-train similar to how an old dial-phone works (except it's transmitting 250kHz signals over the AC line instead of DC pulses).

Do you have the main Jukebox, or just the Wall-O-Matic remote? If you have the transmitter and the receiver and they are working, you should be able to tap-into the relays or the record selector electro-mechanics without worrying about how the 240kHz wireless remote works.

If it's not working, or if you don't have the main jukebox-receiver it's probably best to build something new using only the old selector switches & housing, rather than trying to repair the antique stuff (since you're not trying to do an actual restoration).

Hi DVDdoug!

Thanks for your reply. I have the Wall-O-Matic but not the receiver. And yes, I feared I might have to do something that taps into the mechanical bits of the jukebox, though since it has 20 buttons and theoretically the mp3 shield can only accept 9, I'm going to have to be a bit creative...

I might hunt around for the receiver.

Myself, I would not attempt surgery on the unit. I would try to detect the 250 Khz somehow. A simple AM detector would probably do a nice job.

A hardware filter is required to separate the low frequency and high voltage (mains) from the high frequency and very low voltage 250kHz signal. For safety an isolation of the receiver from mains voltage is required, usually a RF transformer. Then the signal has to be separated/decoded from the 250kHz carrier, before it can be used to control any device. Such a circuit requires some non-fundamental knowledge in electronics, which you may not have.

evenly spaced selection impulses of 250 kilocycles current

I think this means that several little bursts of 250kHz are sent and would normally be detected by the receiver.

I suspect it would not be too difficult to identify the switch that turns on and off the transmitter to send those bursts. The “data” at that switch is what you need. It will have incorporated all of the other actions.

You could then send that data by wire or, for example, using some cheap nRF24L01+ 2.4GHz transceivers.

Or, your Arduino within the Wall-o-matic should be able to decode the “data” and figure out which tune is wanted. It could then send a more “intelligent” message such as “<17>” for Tune 17.

PS Thanks for the link to the wonderful old manual.

I submit that modifying the unit requires almost as much electronics knowledge as designing a receiver. To extract the 250 Khz would not require any fancy transformer. A few turns of wire wrapped around the mains supply line would probably work as a pickup, and could be done without excessive risk. It's at least as safe as the kinds of opto isolated devices that hobbyists build.