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Old 12th June 2003, 04:53 AM   #1
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Question input selector

Hi I need a little help with a little project I want ot build.
I want to build a 4 input selector for a pre amp. I want to use relays to select inputs. I want to use a 4 bit ring counter to do the selection (as in the diagram). Each Q output will be connected to the base of a transistor which will drive a relay. I would use a button to connect the clock input the Vdd (to act as a clock pulse). So each time I press the button the relays would turn on in sequence.
I was thinking that I could use two 74ls74a chips as each chip has two D flip flops and it give access to reset if each Flip flop.

Will this work?
Any suggestions?
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Old 12th June 2003, 07:09 AM   #2
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Default input

No reason why it should not work, but are you sure you don't want the possibility to directly select the input you want, rather then having to step through unused inputs to where you want to go?

Jan Didden
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Old 12th June 2003, 08:56 AM   #3
dhaen is offline dhaen  Europe
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Hi,

It looks to me as if you've made a Johnson binary counter there. The third step will have input 1 an 2 active.
You'll either have to decode with a binary to decimal/ octal decoder (like a 4028), or use a decimal / octal counter (can't remember the number).

There are lots of solutions to the selector question. My favourite is the 74C922 .

Cheers,
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Old 12th June 2003, 10:02 AM   #4
moamps is offline moamps  Croatia
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Hi,
here is my suggestion
(one switch selector, is set for 4 input, maximum is 10)

Regards
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Old 12th June 2003, 03:48 PM   #5
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Hi thanks for the help so far.

dhaen, the circuuit is a ring counter not a Johnson, here is the web page I got the circuit from: http://www.eelab.usyd.edu.au/digital...egister07.html

moamps, very nice circuit there, I might just try it.
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Old 12th June 2003, 04:03 PM   #6
dhaen is offline dhaen  Europe
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Quote:
Originally posted by lawbadman
Hi thanks for the help so far.

dhaen, the circuuit is a ring counter not a Johnson, ...snip...
I stand corrected

Moamps circuit looks good.

Cheers,
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Old 12th June 2003, 04:36 PM   #7
moamps is offline moamps  Croatia
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Quote:
Originally posted by dhaen


I stand corrected

Moamps circuit looks good.

Cheers,

Hi, thanks.
But, I see now one error. MR input must be connected to R1.
Here is god pic. Sorry, guys.

Regards
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Old 10th September 2005, 09:44 AM   #8
cd-i is offline cd-i  Romania
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hello guys,


This circuit seems to me a little bit impractical, I don't like the idea of cicling thru all unused inputs until I reach the good one. I rather use a circuit with a selection button for every input (4 inputs - 4 selection buttons). This is easy to be done with some flip-flops with set - reset inputs and some diodes. If someone is intersted maybe i'll draw a schematic later.

The idea is that the button for one input should give a command on the set input of one flip-flop and reset the rest of the flip flops.
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....I hope this thing works better than it looks....
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Old 10th September 2005, 10:45 AM   #9
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I agree, latched pushbuttons would simplify the circuit.

From the simplistic point of view, and to avoid any digital circuitry implemented in analog pre - amp, why not ditch digital IC's and use only rotary switch that would supply a separate +12 V to high quality relays?

Extreme_Boky
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