Ancient Spirits of Nerdery, I summon you!

Spirits of Old-School Nerdery, lend me your power! From your cinderblocked halls, glowing with the green light of oscilloscope displays, I summon you! From your recumbent bikes, I summon you! I need your Ancient Skills of Electrical Engineering! Please comment this post!

Here are my challenges, O wise ones:

Stepping down DC Power from 18v to 12 and 3v:
The MacGuffin — the AM transmitter that broadcasts the Sekrit Code you need to sign up for Guerilla Drive-In updates — has three components, all of which go in a waterproof (and therefore poorly vented) plastic box:

  • An AM transmitter (requires 18vdc),
  • A Sony Sports Walkman (requires 3vdc. I think. Two AA batteries end-to-end. That’s 3vdc, right?) with a 6-minute endless loop tape in it, and
  • A red radio-shack panel light on the front (claims to be 12vdc).

I want to power everything off of just ONE wall wart, which will live outside the box, and pass in the power through a jack mounted in the box (already done.) I own an 18vdc wall wart, a 12vdc wall wart, and a car adapter that can step 12vdc down to 3vdc. Could I power the transmitter on the 18v wall wart, and also step down the power to 3v for the sports walkman? How would I do that? Just by soldering some resistors into a small Radio Shack project box? Would that end up generating a lot of heat? When you live in a medium-sized town like West Chester, where could you go to get that done? Do you call a small mom-and-pop TV repair shop? How about the 12v light? If I give it 18v, will it explode, or will it just be a little brighter and live a little shorter? Helllllllp!

Attenuating speaker-level output
The 16MM projector has a quarter-inch jack on the front that is used to drive an auxiliary speaker. If I just use an adapter to adapt that to an eighth-inch stereo jack, then plug that into a transmitter, I’m assuming the signal is too… something. Powerful? Does anyone know how to, er… “attenuate” what’s coming out of that quarter-inch jack labeled “speaker”, and make it so it’s… good… for putting into the “audio in” RCA jack in the back of a transmitter? Here’s a picture of the speaker jack from the projector, if it helps any. Does anyone know how do to this, or know what dongle I should get?

Thank you, O Spirits! I will leave a basket of capacitors and a crimping tool under the candles for you.

UPDATE: O spirits, thank you for your replies! I will indeed look into buying voltage convertors from Tyco, since they seem to actually, er… convert the voltage, not just turn the extra voltage into heat in a resistor. Also, I’ll just be taking the wires that go to the battery box in the walkman and wiring the power into that, so the walkman is expecting 3V…?

3 responses to “Ancient Spirits of Nerdery, I summon you!”

  1. I bet that this is something that could be solved by that electrical engineer you discovered in the church basement in NY, though it seems a long way out of the way. I also expect that if you have a local ham radio club, the guys there could help you out. Hams are mainly retired gents who grew up playing with electricity and getting things to work. If you need a bigger selection of wall warts — well, I have a mother lode. Robin left more WWs behind than you could shake a plug at, and many of them were still plugged in and drawing electricity, LOL.


  2. Hi John,
    You can roll your own, but you are probably best off buying a DC/DC converter that fits your needs. Here is a Tyco unit that would work.
    There are many different manufacturers, so if you want to search for DC/DC converters, you can probably find something cheaper. I do like Tyco because they provide a lot of extras and provide clean power.
    BTW, 3.3vdc is a more common voltage, but if your device really requires 3.0vdc you should still be able to run it on a 3.3vdc as it is within the nominal +- 10%.
    I would not give either a 12vdc light or LED a 18vdc feed. Explosion might not (then again, might) happen, but your glory would be short lived and the smoke would probably be carcinogenic.
    Last, you did not mention current, just voltage. The unit I spec’d will give you 3.5A. Hopefully, that’s enough.
    Good Luck!
    — Nick


  3. I have a line level attenuator in a drawer somewhere from back when I used to do a long of manual analog dubbing from sources (thanks Williams Trivia!) I got that at Radio Shack, although seems to be gone from their product catalog.
    I did find guide to how to do yourself out there which may help.


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