Strange how-to question(s)

Hi Dan, The D lines are data lines. The USB port is a sereal connection not audio. There are ways to get the audio into your radio but a schematic would be nice. Sometimes you need only tap the volume control and supply the proper level audio to the radios amp section. I can't tell without seeing a diagram.

Tom

Those USB lines are digital, not analog.

If the radio receives FM, you can get little flea-powered transmitters that connect to the headphone jack and let you listen on the radio.

If it only does AM you can do similar, but you may have to build the thing yourself.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

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Exactly. Just now working up a small AM Tx design for a friend who does old car radios. Goes ... device audio connector, into modulator of battery powered, couple of mW, Tx oscillator, trimmed to Tx in a quiet area of AM band.

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Hello all,

thank you for your messages! Some followup information/questions are following.

The radio is AM/FM; I have used those FM transmitters before, with only mediocre performance.

Are the signals that come out of the headphone jack analog? I would presume so; please correct me if I am wrong. If they are indeed analog, does it follow that those signals could be routed into the amplifier circuit of the vintage radio? If this is feasible, what would I need to do to make sure the signals from the radio reception are not "combined" with the new (mp3 device) signals, resulting in a garbled mess?

Again, thank you for your patience in reading my messages, and for any ideas you may have!

Regards, Dan

Dan: that's exactly what I was thinking of. John is your friend (at least he is if you can get your hands on schematics).

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Yes, the headphone jack signal is analog. So far at least headphones are dumb devices, they don't get signal so much as they get audio drive, which must be analog.

To really do this right you'd need to switch out the audio from the receiver and switch in the audio from the MP3 player. This can be done with varying levels of success and attractiveness by a good audio technician with a schematic of the radio. Someone who's _really_ good may even be able to figure out how to switch the thing over automatically, without putting some out-of-place modern button on your dash.

I'd hate to rip into a vintage piece of hardware like that, though.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

this could be even easyer.. right 2 questions,

1, do you realy need to use the radio... or could you just have it for show.. 2, have you a place to hide small electronic devices... well heres my idea, buy a small amp, set the volume to 50-75% of max of amp, then connect the speakers to the amp connect the mp3 player at low volume then power on. you use the mp3 player volume up and down

Hi Tim,

thank you for the additional thoughts. I suspect a schematic for this radio may be a dinosaur egg. Couple that with the small possibility that I could actually find someone to do the work you suggested makes me think this project is not possible. Tearing into the vintage hardware may not be the best thing, either... However, I will start looking for a schematic now! :-)

Regards, Dan

I have most of the Sams car radio manuals, and they covered US factory radios of that era.

has an online index, or you can download the database for your persoanl use on your computer.

is the online directory.

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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you\'re crazy.

I have a vintage radio book somewhere ("Lamphouse Radio Data Book" (two shillings and sixpence)) that explains how to connect a phonograph pickup to the volume potentiometer of a valve radio...

basically what you do is examine the potentiometer behind the volume knob, it'll have three terminals one is in, one is out, and one is ground,

usually the middle one is out. and one of the end ones is ground, and the other is in.

what you do is disconnect the in wire and connect your programme source (phonoghaph, cd player, whatever) to the in terminal.

if you want to get tricky you can use a switched socket here so unplugging your source will recconnect connect the radio's tuner.

if care is taken this modification will be reversible, so it may not devalue the radio...

Bye. Jasen

Actually, you can do this without a schematic. As Tom Biasi suggested earlier, you need to tap into the volume controls. Find the "top" lug (the one the slider contacts when the volume is at max) and unsolder the wire(s) going to it. (In this vintage radio I suspect that this will be a normal wired connection, not a PC-mount pot.) That wire is the radio's audio signal, and the now-bare top lug is the volume control input to the power amp. If the radio is stereo, then you'd do this for both channels (dual-ganged pot). You then use a DPDT switch (SPDT if mono) to switch that top lug between the orignal wire or the headphone output.

Note that car radios typically have a second function on the same shaft as the volume (either tone or balance), so you need to pay attention to which pot sections are volume... always the inner knob AFAIK.

Depending on the oufput level from the MP3 player, you might need to provide extra attenuation there. Or, if the radio is mono, you might need to add series resistors from each headphone channel to the SPDT lug, to sum them together. (Try 10K)

Other than that, this is a conceptually simple mod, whose difficulty mostly depends on how hard it is to get at the pot lugs. There may be a lot of mechanical stuff in the way due to the station selector, tuning dial, etc.

Best regards,

Bob Masta DAQARTA v4.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter FREE Signal Generator Science with your sound card!

"Bob Masta" >

Hi Bob,

thank you for your input! If I may indulge you with another question that will display my ignorance...

Ok, so now I have my wire coming out of the headphone jack, that I need to splice into the SPDT switch (the radio is mono). I believe that wire will actually consist of two wires in the plug connector. My presumption is I cut off the plug connector, isolate and strip the two wires, splice them together, and solder to one of the posts on the SPDT switch? If they are necessary, where should I insert the resistor(s)?

Regards, Dan

Below shows MONO (2 wire) out from the MP3 to the radio. The resistors aren't needed and you do not splice the two wires in the plug together. One goes to the radio ground, the other goes to the switch.

Radio SPDT Player -----------o o--------------------+ o | | | / ====PlUG \\ | ------->/ | \\ | | | | Gnd --------------------------------+

The resistors are needed if you use STEREO out from the player, and there will be two wires plus ground in the plug.

Radio SPDT Player -----------o o---+---[R]---------+ o | | | +---[R]--------- ====PLug / | \\ | ------->/ | \\ | | | | Gnd -------------------------------+

Usually, the ground wire is a braided shield around the other two wires.

Ed

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Hmmm... that 12V rail could be very noisy. Back in 1968 they may not have appreciated the value of suppression devices on the rails (these days you have a capacitor or something across the spark plugs) - so you probably want some kind of fast voltage clamp on the supply which can protect against fast positive and negative spikes. Not just a zener diode (they may not be fast enough) but perhaps a unidirectional tranzorb. So your supply should probably be something like

12V / 0V rail from battery ---> pass the 2 wires through a tube of ferrite to filter out common mode noise, possibly looping the wires through more than once ---> 1A slow-blow fuse ---> 18V tranzorb across supply ---> 7805 linear regulator, possibly with small heatsink.

On second thoughts the 7805 has a fairly high quiescent current which could drain your battery so you need an on/off switch too.

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Nemo