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Discrete Logic ABX Switch Box

post #1 of 6
Thread Starter 

I'm the kinda guy who designs circuits when I have nothing to do.

So recently I designed an ABX switch box using discrete logic.

Here's my Conceptual Schematic:





It seems to work fine in my simple Java circuit simulator, but I'm not sure if this will really work.

So is there anyone with electronic experience who can give me some feedback?

(anything wrong, improvements?)




Relays aren't drawn here because this simulator doesn't have the reed relays I'll be using.


The "ABX Switch" has a center-off position.

The "Randomize X Switch" is a Push-switch.


The "X" random is generated using a square wave and a human controlled "hold" switch.

Picture it like a wheel of fortune or slot machine if you will.


The "OR" gate in the center that's connected to its own input is used to hold the "X" status,

so that the status of "X" will be the same every time until the "Randomize switch" is pushed



I may switch the NOR gate for an OR gate and Discrete CMOS NOT Gate (Using 2 MOSFETs),

because Logic gates comes in packages of 4s.

Anyone know a small complementary MOSFET pair I could use?

(No surface mount packages)

Edited by akiroz - 9/3/12 at 7:12am
post #2 of 6
Thread Starter 

Just made a practical schematic:

Note: The ABX switch shown is a SP4T Rotary Switch because I couldn't find a SPDT switch with center-off in the library.

Edited by akiroz - 9/3/12 at 10:48am
post #3 of 6

/me envys someone who does something that would melt my brain when he has nothing to do

post #4 of 6
Thread Starter 

Just redesigned my Discrete Logic ABX Switch box.


Rev.B Features:

- Removed unnecessary components 

- De-bounced Switches

- Muting

- Data Logging: Up to 8 test trials




Note: Each relay is suppose to be DPST.


Full discrete logic allows DIY-ers to construct this without Micro-controller programming gear.

Single 5V power requirement allows switch box to be powered by USB.

post #5 of 6

Did you ever end up building the switchbox?


I'd love to get my hands on an ABX comparator, but the only one I'm aware of available commercially comes at the ridiculous 1000$ price-tag:


post #6 of 6

Related question: Does anyone know how to implement ABX-logic in a microcontroller (like Arduino) which could then control relays for input selection?



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