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Resistor-Diode-Relay Logic Source Selector
Resistor-Diode-Relay Logic Source Selector
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Old 16th March 2013, 05:48 PM   #1
pmbrunelle is offline pmbrunelle  Canada
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Default Resistor-Diode-Relay Logic Source Selector

Here is my rough concept for the logic of a source selector. I wanted no microcontroller, and the concept should be easily expandable to a number of inputs.

Desired functionality:
When you push a button, any other active source is deselected, and the new source is connected, even when you release the button.

Buttons are DPDT momentary toggles or pushbuttons.

Relay coils need to be 12 VDC. 5 VDC relay coils have guaranteed turn-off voltages close to the 0.7 V diode drop.

The relay that selects the input might be the same one as for the logic, or it could be separate...

Does this idea make sense?
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Old 17th March 2013, 12:44 PM   #2
Mooly is offline Mooly  United Kingdom
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Resistor-Diode-Relay Logic Source Selector
I don't get it tbh ... you need to draw it much much clearer and with one relay in the conducting state. It seems a very "clumsy" way of doing things tbh, sorry that's not meant as a criticism.

This is a simple selector (I'm sure it came from someone on the forum, maybe Lineup from a few years back) and uses one CMOS chip. No micros, no clocks.
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Old 17th March 2013, 02:32 PM   #3
mickeymoose is offline mickeymoose  Canada
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Here is an interlocking 4 pos. switch schematic, easy to expand. E
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File Type: pdf 4posSwitch.pdf (576.2 KB, 81 views)

Last edited by mickeymoose; 17th March 2013 at 02:34 PM.
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Old 20th March 2013, 03:10 AM   #4
nezbleu is offline nezbleu  Canada
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Resistor-Diode-Relay Logic Source Selector
Here's another one using a single 40174 hex D-type flip-flop, I used it on my preamp.


The momentary switch is the clock for the flip-flop.
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Old 17th April 2018, 02:22 AM   #5
jacmeen is offline jacmeen  United States
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I have built this circuit and with 12v it doesnt latch. It will latch around 7v? what could be wrong?
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Old 19th April 2018, 06:16 PM   #6
PRR is offline PRR  United States
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Originally Posted by jacmeen View Post
I have built this circuit and... what could be wrong?
There's four circuits in this thread. Which one?
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Old Today, 04:26 AM   #7
jacmeen is offline jacmeen  United States
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Sorry, the circuit right above my first post.
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Old Today, 06:39 AM   #8
Calvin is offline Calvin  Germany
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here´s another one, but with the add-on of a temporarily muting output relay.
Similar to the circuit Mooly presented it utilizes a CD4028B and the diodes D1-D4 for a hold-function.
You can connect a 100nF cap across one of the tactile input switches (Cin) to make that input a preset input.
The outputs may be switched by discrete transistors (BC550 etc.), or a transistor-array like the ULN2804 (the ULN2804 is a left-over from a earlier, bigger project, see here )
It´s a break-before-make logic with low sensitivity to switch-over noises, but to be sure one could add a temporare mute function as follows.
Diodes D5-D9 combine the unused outputs of the CD4028B and trigger one half of a CD4098B.
For a time span of the RC-time-constant (Rx1/Cx1, 1M/100nF=100ms) the output is muted.
Adding a simple R-C-D circuit plus transistor (Tr connected in series to the output-Relay transistor) one can also add delayed-turn-On/fast turn-Off functionality.

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File Type: gif 4x In 1x Out - CMOS Relais Controller.gif (315.5 KB, 13 views)

Last edited by Calvin; Today at 06:46 AM.
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