Electronics > Projects, Designs, and Technical Stuff
3 switches, 7 lamps (no solid state)
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Benta:

--- Quote from: ebastler on February 28, 2019, 02:16:01 pm ---
--- Quote from: Benta on February 28, 2019, 01:37:13 pm ---First you do a 2:4 demux using two SPDT switches. One switch connected to L, the other to N. Four lamps are connected between the four outputs from the switches in the four combinations possible. Now you can light each bulb independently.

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Maybe I am misunderstanding, but I think this first stage suffers from the same fallacy as bsudbrink's design: In addition to the desired current path through one lamp, there will be an additional path through two three other lamps connected in series.

I ran out of room on my "DaveCAD" sticky note, hence have not looked at the second stage yet.  ;)

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You're right, I just identified the issue myself.
DDunfield:

--- Quote from: ebastler on February 28, 2019, 03:00:30 pm ---
--- Quote from: DDunfield on February 28, 2019, 01:53:19 pm ---If SPDT relays, then 5 relays - if you can use DPDT then it becomes three.

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Hmm, your diagram seems to show six SPDT relays?

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Sorry, typo - yes 6 relays. If you can use DPDT it still becomes 3.

Dave
ebastler:

--- Quote from: Benta on February 28, 2019, 03:03:02 pm ---
--- Quote from: ebastler on February 28, 2019, 02:16:01 pm ---... I think this first stage suffers from the same fallacy as bsudbrink's design: In addition to the desired current path through one lamp, there will be an additional path through three other lamps connected in series.

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You're right, I just identified the issue myself.

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Yes, those old-fashioned relays, switches and lamps, where current stubbornly flows in both directions, can be buggers to work with!  ;)   

I played with concepts for a relay computer for a while. If you choose "no diodes allowed" as one of your design constraints, you quickly need many relays with many contacts, even for simple bit-serial designs. Diodes help!
Cyberdragon:
I've decided to include the 8th lamp in the final project and just call it lamp 0 (for state 0), just to show that there's always a current path in this arrangement. I also found exactly 3 120V relays in the junk this is to be made from so yay no transformer! ;D

The power will come in through a junction box at the bottom splitting it to the three switches (and box grounds). The relays will be mounted on a rail above the three switches with black wires coming in for main power and the coils and the white neutrals returning to the power inlet box. The lamps will all be at the top with their neutrals and grounds daisy chained before returning to the main box. However, depending on wire size, this may exceed the input box capacity so I might have to split the neutrals and grounds to a seperate box (obviously still grounding the main box). Red interconnects between each relay, and black ouputs up from the relays to each lamp.
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