Author Topic: 3 switches, 7 lamps (no solid state)  (Read 3724 times)

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Online Benta

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Re: 3 switches, 7 lamps (no solid state)
« Reply #25 on: February 28, 2019, 01:37:13 pm »
OK, here goes:
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.

In the second stage you add the third switch that controls two DPDT relays between the first two switches and the lamps. Add a second group of four lamps. The relays switch between the two groups of lamps. Now you have a 3:8 demux. Remove one lamp of your choice, and you can control all seven lamps individually, plus turn them all off.

 

Offline mikerj

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Re: 3 switches, 7 lamps (no solid state)
« Reply #26 on: February 28, 2019, 01:37:41 pm »
Sorry for the ugly drawing, I don't have access to a real tool right now...
Anyway, is there any reason this wouldn't work:

This suffers from a trap that is very easy to fall into when using relay logic.  In any position, one of the eight lamps will be at full brightness, but the lamp it is paired with has a path to ground through the other three pairs of lamps.  This means the paired lamp will illuminate but at lower brightness and the rest of the lamps may also glow dimly if there is sufficient current.
 

Offline DDunfield

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Re: 3 switches, 7 lamps (no solid state)
« Reply #27 on: February 28, 2019, 01:53:19 pm »
i'm trying to come up with a system to switch 7 lamps on (indevidually) with 3 spdt switches and relays (just for funsies).

I'm trying to figure out the most efficient wat to do it. Getting the light to switch on when all switches are on is easy, when all switches are on, none of the secondary switch contacts have power which shuts of a spdt relay that disconnects the common from most lamps and connects it to the remaining lamp. Each switch is connected to a light through the nc contacts of other relays.

What I'm still trying to figure out is the logic that drives the other three lamps.

Aslo, the current circuit requires the same voltage for coils and lamps. So I'd have to have a different circuit using dual pole relays for different voltages (IE LV coils and mains bulbs).

If SPDT relays, then 5(**) relays - if you can use DPDT then it becomes three.
**EDIT - apparently I can't count - It's 6 relays if SPDT - still becomes 3 with DPDT **

If S1 cannot be DT then add a relay.
If S2 can be DPDT then subtract two relays (or 1 with DPDT relays)
If S3 an be 4PDT then subtract 4 relays (or 2 with DPDT relays) - ie: no relays at all assuming S2 is DPDT

Dave
« Last Edit: February 28, 2019, 03:10:50 pm by DDunfield »
 

Offline ebastler

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Re: 3 switches, 7 lamps (no solid state)
« Reply #28 on: February 28, 2019, 02:16:01 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.

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.  ;)

Edit: Just saw your post pop up and disppear again. Your diagram is the same as what I have on my sticky note, and I guess you did spot the unwanted path after posting.  ;)
« Last Edit: February 28, 2019, 03:04:12 pm by ebastler »
 

Offline ebastler

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Re: 3 switches, 7 lamps (no solid state)
« Reply #29 on: February 28, 2019, 03:00:30 pm »
If SPDT relays, then 5 relays - if you can use DPDT then it becomes three.

Hmm, your diagram seems to show six SPDT relays?
 
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Online Benta

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Re: 3 switches, 7 lamps (no solid state)
« Reply #30 on: February 28, 2019, 03:03:02 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.

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.  ;)

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

Offline DDunfield

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Re: 3 switches, 7 lamps (no solid state)
« Reply #31 on: February 28, 2019, 03:09:05 pm »
If SPDT relays, then 5 relays - if you can use DPDT then it becomes three.

Hmm, your diagram seems to show six SPDT relays?

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

Dave
 

Offline ebastler

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Re: 3 switches, 7 lamps (no solid state)
« Reply #32 on: February 28, 2019, 03:26:35 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.
You're right, I just identified the issue myself.

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!
 

Offline CyberdragonTopic starter

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Re: 3 switches, 7 lamps (no solid state)
« Reply #33 on: March 01, 2019, 06:11:05 am »
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.
*BZZZZZZAAAAAP*
Voltamort strikes again!
Explodingus - someone who frequently causes accidental explosions
 


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