# Octagon with Expression Input



## Hexjibber

Hi, this is my first post to this forum but thought it appropriate to share this build.

I will start by saying a big thanks to Madbean forum member *bsoncini* for their post on adding an expression pedal control to the Octagon, it was really clearly written as well as just being a great idea! 

I've really enjoyed the project overall being my first delve into the realms of FV-1 and also PedalPCB, thankfully the board and instructions made it simple and easy so thanks for that!

The box is etched with NaOH (caustic soda/lye) with a few coats of clear for good measure. Here's the pics...


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## zgrav

nice design, and a clean build.


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## Chuck D. Bones

Beautiful!  Nice clean build inside & out.  Can you expound on the etching method, i.e. how do you transfer the pattern to the surface?


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## the_grumpy_gnome

This is beautiful. I love the original design.  Expression pedal?!  Can you please post the link? I'd like to add one to mine.


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## geekmacdaddy

Stunning work.


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## Jbanks

the_grumpy_gnome said:


> This is beautiful. I love the original design.  Expression pedal?!  Can you please post the link? I'd like to add one to mine.


Here’s bsonici’s original post on it. 






						Pedalpcb Octagon with expression jack
					

Pedalpcb Octagon with expression jack



					www.madbeanpedals.com
				




I’ve also been looking for a couple weeks on line at adding EXP jack in general. Here’s some other links on the topic. 



			http://www.geofex.com/Article_Folders/xprnped.htm
		








						How to include a CV/expression pedal input
					

How to include a CV/expression pedal input



					www.madbeanpedals.com


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## the_grumpy_gnome

Jbanks said:


> Here’s bsonici’s original post on it.
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> Pedalpcb Octagon with expression jack
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> Pedalpcb Octagon with expression jack
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> www.madbeanpedals.com
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> I’ve also been looking for a couple weeks on line at adding EXP jack in general. Here’s some other links on the topic.
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> http://www.geofex.com/Article_Folders/xprnped.htm
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> How to include a CV/expression pedal input
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> How to include a CV/expression pedal input
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> www.madbeanpedals.com


Thank you!


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## Jbanks

Always have to keep missing the pedals! Another fun addition is a 2knob job PCB. It adds a second pot for 2 different settings that can be switched between with a 3pdt. Great for those infinite feedback swells or a major gain boost.


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## the_grumpy_gnome

I'm interested in swinging the pitch up or down on the pitch-shifted delay.


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## Jbanks

the_grumpy_gnome said:


> I'm interested in swinging the pitch up or down on the pitch-shifted delay.


It does get weird sometimes transitioning between one pot and the other. Not exactly portamento style slides, but rougher.


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## Hexjibber

Thanks a lot everyone, I'm really pleased with this build overall 

I did link to the original Madbean post in my post but the link colour on the forum is almost the same as the body text so makes it hard to see. I see it's been posted further up though so all good! Definitely worth a try if you're interested, just add an extra level of fun to it.


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## Hexjibber

Chuck D. Bones said:


> Beautiful!  Nice clean build inside & out.  Can you expound on the etching method, i.e. how do you transfer the pattern to the surface?



Thanks! 

I have a tutorial I did a while back on how I do etching, hopefully it may be of some use? I did it a good few years ago but my method hasn't changed at all in that time. Any questions though just give me a shout!

https://diy-guitar-effects.tumblr.com/etching


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## ChrisSchwarzkopf

Wow, thats pretty cool! does this work with the Arachnid (+custom EEPROM)?


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## Hexjibber

ChrisSchwarzkopf said:


> Wow, thats pretty cool! does this work with the Arachnid (+custom EEPROM)?



I would imagine so but did not come up with the mod myself, however in the original Madbean post referenced above someone had a similar question and it looks to be the case based on the fact the pots follow the same circuitry.


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## phi1

ChrisSchwarzkopf said:


> Wow, thats pretty cool! does this work with the Arachnid (+custom EEPROM)?



The octagon is actually the exact same thing as the arachnid, it just comes with the octagon eeprom. if you download the build docs, they are identical (they say arachnid on the top). The module8 is also identical, with the module8 eeprom. So, yeah this mod would work the same.


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## ChrisSchwarzkopf

Awesome! Cant wait to build that thing


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## ChrisSchwarzkopf

Hey, i am ready to build the thing and was wondering which jack i Need to buy for the expression input?


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## K Pedals

ChrisSchwarzkopf said:


> Hey, i am ready to build the thing and was wondering which jack i Need to buy for the expression input?











						6.35mm 1/4" Stereo Insulated Switched Socket Jack Solder Lugs
					

Get It Fast - Same Day Shipping




					www.taydaelectronics.com


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## ChrisSchwarzkopf

K Pedals said:


> 6.35mm 1/4" Stereo Insulated Switched Socket Jack Solder Lugs
> 
> 
> Get It Fast - Same Day Shipping
> 
> 
> 
> 
> www.taydaelectronics.com



Awesome, many thanks!


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## ChrisSchwarzkopf

Hey, I am still waiting for my Arachnid PCB which is currently enjoying it's time with German Customs for almost 4 weeks now /). In the meantime I spend my time designing the enclosure and everything and was also wondering how the rotary switch for the Expression Input actually works. I bought the switch shown in the picture and am unsure about the pin numbering. Can someone tell me which pins are A. B and C and which ones are 1 to 12?


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## Chuck D. Bones

I used a DMM to figure it out on mine.  Did you look online for the datasheet?


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## ChrisSchwarzkopf

Yeah I couldnt find any datasheet :/ i do have a DMM yet no clue what to do with it on a switch like this


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## Chuck D. Bones

The inner three terminals are A, B & C.  Which one you call "A" is arbitrary.  Put a mark with a sharpie next to the terminal you want to call A.  We will call the outer terminals A1, A2, A3, A4, B1, B2 and so on.  Makes more sense than calling them 1 thru 12.  Set your DMM for BEEP if it has that setting, otherwise set it for the lowest Ohms range. 
1) Rotate the switch full CCW (as viewed from the knob side). 
2) Connect one lead of the DMM to A.
3) Touch the other DMM lead to the outer terminals near A until you get a BEEP or a resistance reading near zero.  The terminal that beeps (or reads zero) is terminal A1.  Put a mark with a sharpie next to terminal A1.
4) Rotate the switch one click CW and repeat step 3.  The terminal that beeps is A2. 
5) Repeat step 4 for terminals A3 & A4. 
6) Rotate the switch full CCW.
7) Move the DMM lead from A to the next inside terminal, we'll call that one "B."
8) Perform steps 3 - 5 to find terminals B1 - B4, but don't make any marks.
9) Repeat steps 6 - 8 to find terminals C1 - C4.

Make sense?


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## ChrisSchwarzkopf

Chuck D. Bones said:


> The inner three terminals are A, B & C.  Which one you call "A" is arbitrary.  Put a mark with a sharpie next to the terminal you want to call A.  We will call the outer terminals A1, A2, A3, A4, B1, B2 and so on.  Makes more sense than calling them 1 thru 12.  Set your DMM for BEEP if it has that setting, otherwise set it for the lowest Ohms range.
> 1) Rotate the switch full CCW (as viewed from the knob side).
> 2) Connect one lead of the DMM to A.
> 3) Touch the other DMM lead to the outer terminals near A until you get a BEEP or a resistance reading near zero.  The terminal that beeps (or reads zero) is terminal A1.  Put a mark with a sharpie next to terminal A1.
> 4) Rotate the switch one click CW and repeat step 3.  The terminal that beeps is A2.
> 5) Repeat step 4 for terminals A3 & A4.
> 6) Rotate the switch full CCW.
> 7) Move the DMM lead from A to the next inside terminal, we'll call that one "B."
> 8) Perform steps 3 - 5 to find terminals B1 - B4, but don't make any marks.
> 9) Repeat steps 6 - 8 to find terminals C1 - C4.
> 
> Make sense?


Thats super helpful, thanks a million ?


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## ChrisSchwarzkopf

Hey there, it's me for the last time (hopefully). I couldn't measure the Switch myself due to a bad MM but asked the people at Musikding, where I ordered the switch if they could help me. They told me that the order of pins is the one you can see in the picture, so I wired the thing up last night. It works perfectly fine but for some reason pot 1 and 3 see to have been interchanged (1 is 3 now and vice versa). Can you verify, that the order of pins is correct? Should I maybe just swap the cables that go to A and C on the switch?  Oh, I couldnt test the expression pedal function so far as my pedal is broken, but I've got a new one coming soon


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## Chuck D. Bones

Recheck your wiring first.  Then try Swapping A & C on the switch, it should work.  You really need a working DMM.  They are pretty much free here in the US if you wait for when Harbor Freight gives them away as a promotion.  I'm assuming you're in Deutchland.  I don't know if the German people would allow a Beschissener Werkzeugladen like Harbor Freight in their country.  Amazon has DMMs for under $10.


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## ChrisSchwarzkopf

Chuck D. Bones said:


> Recheck your wiring first.  Then try Swapping A & C on the switch, it should work.  You really need a working DMM.  They are pretty much free here in the US if you wait for when Harbor Freight gives them away as a promotion.  I'm assuming you're in Deutchland.  I don't know if the German people would allow a Beschissener Werkzeugladen like Harbor Freight in their country.  Amazon has DMMs for under $10.



Thanks!! Yeah I am in Germany and of course you can buy DMMs here as well ;D I do have one thats ok but I couldn't get it to work in the way you suggested so I asked the people at the shop where I bought the switch. Anyway, I will check the wiring and then test out changing the two wires @ A and C


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## ChrisSchwarzkopf

I finalized the project (and will post pics soon) and everything works as it should, hallelujah! )) Thanks for your awesome assistance. Only thing I was wondering about: With my expression Pedal (A Moog EP-3) it seems to have the wrong polarity (is this the right word?), for example I expected the Tremolo Speed to go up when I push down my toes but its the other way round. Not really a problem but I wondering if I can easily reverse that, for example by swapping the two leads that go to the outer terminals of the expression jack?


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## Metthoden

I would like to do the same build. But I have got a different kind of switch laying around. 
You can see in the pictures: 


https://imgur.com/wuCTuIw




https://imgur.com/LlADhJc


It is a 3-way switch.

Can I use this switch to realize this modification? Can someone give me a clue how to wire it?
That would be awesome.


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