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stuck on GEO a/b/y

8/9/2000 11:17 PM
jeremy spake
stuck on GEO a/b/y
i am really close to completing GEO's aby box project, and i came to an unsettling conclusion a few moments ago...  
i am going by the instructions here:  
i don't understand how the power supply works here. on the parts layout page there doesn't seem to be a way for the power to switch. i assume that is why he linked to the splitter project. the only thing is, there is no way i can fit another circuit into this box to make it switch that way. -not with the batteries in there too. there's just not enough room. is there such a thing as a bipolar wall wart for something like this? how would i piecs all that together?  
i appreciate any assistance you can give me here.  
-jeremy spake
8/9/2000 11:46 PM
I think you're right - as shown, the power supply is not switched on or off, just the ground is removed from the input jack if the jack switching is used.  
I haven't put a PCB together for this one yet. The PCB layout I did for the isolated splitter precursor to the A/B/Y box included transistors to switch the battery power on and off with only the input jack grounding trick. But that's another story. For the power as shown, you'll need a separate power switch to do it easily and if you're limited on board space.  
You have some options. You can power it from two 12V cylindrical batteries. There are 6V and 12V camera batteries that are slightly smaller than the size of a AA cell. This will give shorter battery life than the 9V's, but might do what you want.  
You can also rig any AC wall wart to make bipolar power by using a half wave rectifier. One lead of the wart goes to ground, one to the junction of two diodes. One of the diodes connects Anode to cathode to a plus side capacitor, the other diode is cathode to anode to a minus side capcitor. You need relatively big capacitors to get enough filtering, so I recommend following this up with regulators like 7809 and 7909.  
You can also do a charge pump inverter. This is an 8 pin dip and three capcitors that makes -9V from the +9V battery you already have.  
I guess I need to make a PCB set to make this fit in a 1590BB. Never tried that, nor have I examined JD's boards for fit.
8/10/2000 12:30 AM
jeremy spake

thanks RG.  
is there a picture or schematic anywhere that illustrates the wall wart conversion that you are talking aout? this seems like it would be over my head without a little more explaination. especially toward the end... my electronics background is rather shallow, unfortuanatly. what about the charge pump inverter? there *might* be enough room for a singke battery and something small like that.  
as a last ditch, i may have to settle for the camera batteries... do you have any suggestions on attaching them to the circuit. -i mean i assume they don't clip on like a 9v.  
oh, would the power supply in craig anderton's book (the yellow, newer one) work here?  
thanks again!  
jeremy spake
8/10/2000 8:05 AM

I normally don't show any power switching options or power switch wiring on any of my projects. Why?...because _I_ normally don't wire any power switching since I never use batteries...and I never use batteries especially on bipolar powered units :) Yes, I live in the world of "Me". Sorry if this caused you grief. I stated the lack of power switching for all projects in the General Build Instructions, but I think I need to mention it in each of the build instructions. Of course if R.G. comes up with a new layout (and maybe RTS board) the world will be a better place, thanks R.G.  
I believe that board will fit in a 1590BB if you float the board along the bottom, the way MXR used to do and position the switches and jacks just right. I haven't actually done it though.  
BTW, make sure to access the site at the new location:  
The fortunecity stuff no longer gets updates in a timely manner.  
8/10/2000 7:38 PM
jeremy spake
help with transformer
me again...  
i am looking through my mouser catalog for an 18v wall wart adaptor or transformer, and i can't seem to find one. does anyone know where to find something like that that i could use on this switch?  
or maybe i should just wait 'till RG has time to make a new PCB.... i'm frustrated.  
thanks for your continued help.  
-jeremy spake
8/10/2000 7:51 PM
You could try these Mouser Wall-wart transformers:  
412-218054, 18vac/500ma, $5.49  
412-215042, 15vac/500ma, $5.49  
page 249, catalog number 601.
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