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Old 11th March 2011, 05:33 AM   #1
icydash is offline icydash  United States
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Join Date: Mar 2011
Default Routing guitar signal between two paths?

Hey guys. So I'm trying to design, an idea of which is below:

Click the image to open in full size.

The idea is that when the Xbee receives the "ON" signal, it will control the switching circuit, sending the input signal (guitar) into the A/D converter of the microcontroller. When the Xbee receives the off signal, it will control the switching circuit, sending the input signal around the microcontroller to the output (true bypass).

The question is: what should I do for the switching circuit? haha. I'm not really sure how to design this / if there are any adequate ICs.

I was thinking of using a relay, but I'm worried about the possibility of "pop" etc that could occur given the electromechanical nature of relays.

Thanks in advance!
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Old 11th March 2011, 04:39 PM   #2
icydash is offline icydash  United States
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Woops that was supposed to be "Hey guys. So I'm trying to design a circuit, an idea of which is below."
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Old 11th March 2011, 10:44 PM   #3
Enzo is offline Enzo  United States
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Relays don't make pops because they ar electromechanical, they make pops because the circuits they switch are left unterminated or improperly terminated. That means when the contacts close, two things at differeing DC voltages are connected. SOme cap has to charge or some other action has to occur to get those voltages the same, and a pop results.

SO you want an AB switch that is relay contriolled instead of stomp switch.

I am not familiar with Xbee, can you link a schematic or at least enough tech specs to know what we are working with? If it is a remote control system, and it already has an output that toggles off and on that we can use, then interfacing it to a relay should be simple.

If you just can't abide relays, then a similar circuit could be made with JFETs, or even a couple op amps.
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Old 12th March 2011, 01:17 AM   #4
icydash is offline icydash  United States
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Quote:
Originally Posted by Enzo View Post
Relays don't make pops because they ar electromechanical, they make pops because the circuits they switch are left unterminated or improperly terminated. That means when the contacts close, two things at differeing DC voltages are connected. SOme cap has to charge or some other action has to occur to get those voltages the same, and a pop results.

SO you want an AB switch that is relay contriolled instead of stomp switch.

I am not familiar with Xbee, can you link a schematic or at least enough tech specs to know what we are working with? If it is a remote control system, and it already has an output that toggles off and on that we can use, then interfacing it to a relay should be simple.

If you just can't abide relays, then a similar circuit could be made with JFETs, or even a couple op amps.
Thanks for your reply. Basically, yes -- I'm trying to make an A/B switch that is relay controlled (or rather, remotely controlled using the Xbee). I wouldn't focus too much on the Xbee, I'm just using that to receive the wireless signal, which simply tells the microcontroller how to control whatever the switching circuit is, whether it be a relay or JFET's or op amps. Effectively what you'll be working with is a pin on the microcontroller going to 5VDC (high) when the circuit is "on", and going to ~0VDC when the circuit is in the "off" position.

So basically i just need to be able to switch between two different channels, like an A/B box, using 5VDC to put the signal down one path, and 0VDC to send the signal down the alternate path.

Does this help at all?
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Old 12th March 2011, 01:20 AM   #5
icydash is offline icydash  United States
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So the "control" you see in the image is really just a pin on a microcontroller, likely an ATMEGA168, going either high or low, depending on what the Xbee tells it to do.

I would love to hear more about your op-amp and JFET possible solutions; as I'd really rather use something like that than a relay.

Thanks again for your post.

I wish I could just edit my above post and put this stuff in, but for some reason diyAudio doesn't seem to allow editing of posts.
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Old 12th March 2011, 01:55 AM   #6
RJM1 is offline RJM1  United States
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Something like this? Three Ch not 2 but you could use it.
http://focus.ti.com/lit/ds/symlink/cd4052b.pdf
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Old 12th March 2011, 04:36 AM   #7
benb is offline benb  United States
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As RJM1 posted, the old CMOS analog switches such as 4066 will work, if you bias your audio into the switches at 2.5V, midway between ground and the power supply. That'll work but you need to add capacitors and resistors, and do it "right" so there will be no popping on switching, bla bla bla.

There are other, more modern solutions that allow +/-15V (common op-amp power voltage range) signal range and still have 0 to 5V control voltage range here:
Analog Switches and Multiplexers - Maxim
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Old 13th March 2011, 12:25 AM   #8
icydash is offline icydash  United States
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Quote:
Originally Posted by benb View Post
As RJM1 posted, the old CMOS analog switches such as 4066 will work, if you bias your audio into the switches at 2.5V, midway between ground and the power supply. That'll work but you need to add capacitors and resistors, and do it "right" so there will be no popping on switching, bla bla bla.

There are other, more modern solutions that allow +/-15V (common op-amp power voltage range) signal range and still have 0 to 5V control voltage range here:
Analog Switches and Multiplexers - Maxim
Those maxium switches look like they're exactly what I need, but unless I'm reading these wrong, I can't find any in a DIP package (or something else easily prototypable on a breadboard). Do you have any tips for using one of these with a breadboard?
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Old 13th March 2011, 12:30 AM   #9
icydash is offline icydash  United States
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something like this MAX4714 0.8-Ohm, Low-Voltage, Single-Supply SPDT Analog Switch in SC70 - Overview seems to be just what I'm looking for, if it was in DIP.


I'm also not entirely sure what the various "on resistance" parameters mean / if they're at all important to me. For example, with the MAX4714 (linked to above), it says the Ron = 0.8 ohms max for a 3v supply... What's that mean?
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