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Old 2nd July 2009, 12:15 PM   #1
Simo88 is offline Simo88  Italy
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Default Input selector

Hi everybody!
I am triying to realize an input selector using relays;
I am looking for a selector that gives the possibility to switch from an input to another one pushing a button (one click >> the next input source...) or using a button for each input source...

I found this scheme but i don't understand what the first part does...
The CD4017 should be a counter (the outputs are sequences like 1000 0100 0010 0001...) driven by its clock enable input...Each output of the counter drives a bjt, and the bjt drives the input relay; Is it right?

I don't understand what the 3 nands do... Could anyone explain me what the first part of the circuit does?

Thanks,
Simone
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Old 2nd July 2009, 12:33 PM   #2
SY is offline SY  United States
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I'm no expert in logic circuits, but the NANDs look like an anti-bounce circuit to give "clean" switching.
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Old 2nd July 2009, 02:36 PM   #3
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Default Re: Input selector

Quote:
Originally posted by Simo88
Hi everybody!
I am triying to realize an input selector using relays;
I am looking for a selector that gives the possibility to switch from an input to another one pushing a button (one click >> the next input source...) or using a button for each input source...

I found this scheme but i don't understand what the first part does...
The CD4017 should be a counter (the outputs are sequences like 1000 0100 0010 0001...) driven by its clock enable input...Each output of the counter drives a bjt, and the bjt drives the input relay; Is it right?
It' right.
What it seems wrong in the schematic is the clock / enable wiring because clock pin 14 is hard wired to 12 V while enable pin 13 is wired to the nand output. I think the two pins had to be swapped.
Quote:
I don't understand what the 3 nands do... Could anyone explain me what the first part of the circuit does?
AFAIK U1A and U1B are a sort of monostable multivibrator (as SY stated for anti-bouncing purpose) whose output feeds (would feed) the counter clock while U1C feeds the counter reset pin.

As you briefly push the S1 Pushbutton you trigger the monostable input and send a pulse to the counter while if you push the S1 Pushbutton longer than roughly 1 second (R3 C2 time constant) you reset the counter

If you are interested in using a button for each input source tomorrow I'll post a schematic.

PS As SY arrived first with the right answer you owe him olive all'ascolana and a verdicchio wine bottle :-)
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Old 3rd July 2009, 02:54 PM   #4
Simo88 is offline Simo88  Italy
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Thank you very much!
I have never seen a multivibrator with nands...now the circuit is more clear; this is the only scheme i have found... if you have another scheme could you please post it?
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Old 3rd July 2009, 10:30 PM   #5
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Quote:
Originally posted by Simo88
Thank you very much!
I have never seen a multivibrator with nands...now the circuit is more clear; this is the only scheme i have found... if you have another scheme could you please post it?
The schematic is a littke bit more complex than your.

The first schematic is a block diagram
The second one is the complete analog diagram
The third one is the logic diagram and the relays drivers

I didn't post the RIAA schematic

As you can see the schematics are from Audio Review feb 1983

I hope that all the schematics are readble. If not ask.
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Old 3rd July 2009, 10:48 PM   #6
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The second schematic
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Old 3rd July 2009, 10:50 PM   #7
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The third schematic
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Old 3rd July 2009, 10:51 PM   #8
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You can debounce in hardware or software, or both -- here's an interesting guide:

http://www.ganssle.com/debouncing.pdf
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Old 7th July 2009, 02:48 PM   #9
Simo88 is offline Simo88  Italy
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Thanks for the schemes...
It's quite difficult to read them... where can i find a copy of audioreview? is it possible to find it on the net or to order it?
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Old 7th July 2009, 03:30 PM   #10
Telemin is offline Telemin  United Kingdom
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I am at work now so i'll be brief, but surely a nice simple method of debouncing is just to use a schmitt trigger?

I'll post a schematic when I get home...
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