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 Forum index » DIY Hardware and Software » Circuit Bending
[Help] Making an external box with switches/patch cables?
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limonpower



Joined: Oct 06, 2016
Posts: 1
Location: Missouri, USA

PostPosted: Thu Oct 06, 2016 1:33 pm    Post subject:  [Help] Making an external box with switches/patch cables? Reply with quote  Mark this post and the followings unread

Hey there, I am trying to make a plug of some sort that I can use to connect switches to contacts with cut traces (sorry for horrible grammar, I'm not sure quite how to put it into words). Basically what I am trying to achieve is a way to have a switch be able to turn on or off communication between two points on a circuit board, but also be able to unplug the box with the switches and have the communication be always on. I know how to make a simple external box for switches, but it would either always be attached, or when removed, the communication would always be off between points.
Here's a quick mock-up I made in Paint of kinda what I'm looking to achieve:
Posted Image, might have been reduced in size. Click Image to view fullscreen.
The orange parts are cuts made on traces. So basically I want the red wires and blue wires to be connected when the external thing with switches is unplugged, but disconnected when the switches are plugged in, so that the switches control whether the wires connect or not.
If it makes any sort of difference, I will need about 16 wires in the plug connecting 8 sets of 2 points on the board.

This is for a Yamaha PSS-270, and I am just trying to keep it looking close to original Smile

The simplest solution I have been thinking about is using 2 8-pin din ports and just connecting them with a short male-male cable when the switches aren't connected. I am not really a fan of this though, since it would require that cable all the time, and it would take 2 cables when the switches are plugged in.


Thanks in advance for any help! I can answer any questions you have about what I am trying to say, I understand that I'm not great with putting my ideas into words.
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Bogus Noise



Joined: Jun 03, 2009
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Location: Sheffield

PostPosted: Sat Feb 04, 2017 5:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I haven't tried but thought about it a bunch in the past, and I feel like this is possible with a 2n3906 for each pair of wires that you want to have reconnect when you unplug the box.

Voltage flows through the transistor from C to E when nothing is connected to the B leg, and when you apply a control signal the voltage stops. So my thinking is that if you join two pins of the multi-plug on the box side, and on the toy side solder one pin to the +V and the other pin to the transistor(s), the external box will the act as a switch. Check the datasheet though as you may also need a resistor on the transistor's base!

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Cfish



Joined: Feb 24, 2016
Posts: 451
Location: Indiana

PostPosted: Sat Feb 04, 2017 8:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

If it's only 4 wires, 2 contacts. They make 1/4 inch jacks that close a switch when the male jack is pulled out.

I think they are called normalized jacks

You would need 1 jack for each switch. But if it's only 2 you need. That's not too bad.

I'm sure they make them in 1/8 inch too.

Ones I bought recently look like this


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Cfish



Joined: Feb 24, 2016
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PostPosted: Sat Feb 04, 2017 8:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Found one on eBay and took a screenshot


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Bogus Noise



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PostPosted: Sat Feb 04, 2017 8:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, the original post states 16 wires, so they're looking for a more multipole solution. Then again, I've only just noticed that the post was from last October!
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Sun Feb 05, 2017 4:51 am    Post subject: Reply with quote  Mark this post and the followings unread

It desn't matter if the post is from october, even if it would be a couple years old it is still interesting.

Usually for something where you want a closed connection when nothing is plugged in I would indeed use jacks with a switch contact,
but with so many wires that's a lot of cables to connect it to the box. I would not use the type you posted from ebay btw. Even though
those are Switchcraft and probably good quality (pretty expensive too) I don't have a good experience with switch contacts on those
open kind of sockets. The closed ones which you posted a picture of usually work a lot better and I personally use the Neutrik NYS216
or similar which have never failed me.

The transistor idea is interesting although I am not sure if it would close the circuit when nothing is connected to the base of it. I'd expect
at least a resistor to GND is needed to make it work. If it will work also depends on the signals that are being switched, there is actually
a change of destroying something this way. But the idea to use remote controlled switching is good. I think using CMOS switches like the 4066
or 4016 could work great for it. Use high value pull up resistors on the control inputs so they are closed when nothing is connected and lower
value resistors to GND in the box so they are open when plugged in. Then let the switches connect them to the positive rail.

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gdavis



Joined: Feb 27, 2013
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PostPosted: Sun Feb 05, 2017 9:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Ya, anything involving transistors would require moding the instrument with active circuitry (connecting to power and ground) and a little engineering.

The switched jacks are the simplest solution but cumbersome for more than a few connections.

The two 8-pin din connectors with a dummy cable might be on track for a better passive solution with a large number of connections, but instead I would probably use d-sub connectors. Put all the connections in one d-sub, and make a dummy d-sub that would plug into it when the switch box isn't connected and bridge the appropriate pins.

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