Search:
Submit Search


Wiring an Expression Pedal - question for electronic gurus

Connecting Hauptwerk to MIDI organs, sequencers, ...

Wiring an Expression Pedal - question for electronic gurus

Postby damuehlbauer » Fri Feb 23, 2018 3:34 pm

I bought an expression pedal from eBay that had a kick switch (for Sostenuto). The expression pedal, however has four wires, not the three that I expected with a typical potentiometer. The seller did not know what brand or type of organ/keyboard this pedal came from, and there were no instructions.

Any of the electronics experts out there have any ideas of how to connect this to my midi board (which is assuming a normal potentiometer)?

Sorry for the dorky illustration below. I'd be happy to email a photos if that would be more helpful.

=========|
=========|
= PEDAL =|
=========|
=========|__
=========|....|<----------- A
=========|....|
=========|__|<----------- B
=========|
=========|
_________|
|______|
... ^ .. ^
... C . D

A=Gray wire
B=Black wire
C=Black wire grounded to base
D=Gray wire

A & B are attached to something that looks like it could be a variable resistor
damuehlbauer
Member
 
Posts: 36
Joined: Fri Feb 09, 2018 5:23 pm
Location: Arizona

Re: Wiring an Expression Pedal - question for electronic gur

Postby engrssc » Fri Feb 23, 2018 7:07 pm

If you have an deBay item number, we may be able to identify the pedal configuration. Do you see a potentiometer?

Rgds,
Ed
User avatar
engrssc
Member
 
Posts: 5510
Joined: Mon Aug 22, 2005 11:12 pm
Location: Roscoe, IL, USA

Re: Wiring an Expression Pedal - question for electronic gur

Postby damuehlbauer » Fri Feb 23, 2018 7:24 pm

It does not seem to contain a typical rotating potentiometer. It has a small panel that seems to slide down within another part, possibly some sort of sensor. Nothing like I have ever seen.

The original eBay listing was https://www.ebay.com/itm/ORGAN-EXPRESSI ... 3136972257

Not sure this will work, but if it does these are photos of the inner workings of the pedal:

https://photos.app.goo.gl/rayhh63MYLGbozoh2
damuehlbauer
Member
 
Posts: 36
Joined: Fri Feb 09, 2018 5:23 pm
Location: Arizona

Re: Wiring an Expression Pedal - question for electronic gur

Postby engrssc » Fri Feb 23, 2018 7:56 pm

Definitely not a potentiometer type expr ped. You may be able to "salvage" the kick switch, which in it self, is probably worth what you paid for the entire assembly. The easiest would be to create a linkage to operate a slide type linear pot. Unfortunately I don't have a picture right now of what I did in that way to add an extra pot to each of my Rodgers 340 expr peds. I know several others have done the same thing, so it can be done. For instance John Kinkennon http://forum.hauptwerk.com/memberlist.php?mode=viewprofile&u=12956 also took pictures of his version.

The other option is buy (another) expr ped with a pot already installed, even if it's not the correct value, that's easily changed.

https://www.ebay.com/itm/old-Organ-Crescendo-Expression-Swell-Shoe-pedal-DIY-hauptwork-steampunk/401496062295?hash=item5d7b07b957:g:kQsAAOSwEW9ajC08

The kick switch could be transferred to the above mentioned expr ped.

Here's a pair, a bit more expensive, but possibly in better shape that would work:

https://www.ebay.com/itm/Pair-Swell-Shoes-Pedals-Rodgers-Allen-Hauptwerk-Good-Condition/112827324235?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D49923%26meid%3Da6f20f59389d40ff87d4356c0deb3924%26pid%3D100005%26rk%3D6%26rkt%3D6%26sd%3D401496062295%26itm%3D112827324235&_trksid=p2047675.c100005.m1851

You can "ring out" the kick switch contacts with an ohmmeter or continuity checker.

Rgds,'
Ed
User avatar
engrssc
Member
 
Posts: 5510
Joined: Mon Aug 22, 2005 11:12 pm
Location: Roscoe, IL, USA

Re: Wiring an Expression Pedal - question for electronic gur

Postby damuehlbauer » Fri Feb 23, 2018 8:27 pm

I agree, I may just need to cobble together something from two pedals. I tested the kick switch and it works fine. I was just taking a chance that someone in the HW forum had seen this thing before and knew how to make it work.

Always an adventure!
damuehlbauer
Member
 
Posts: 36
Joined: Fri Feb 09, 2018 5:23 pm
Location: Arizona

Re: Wiring an Expression Pedal - question for electronic gur

Postby organtechnology » Fri Feb 23, 2018 11:19 pm

The pedal shown is an optical pedal where the amount of light let through by the blade looking thing is converted to a resistance value by a photo resistor. The impedance is high and non-linear. Salvage the kick switch and maybe the pedal mechanism and build a slide potentiometer pedal out of plastic kitchen cutting board, toilet water level hardware, a slide potentiometer from spark fun.

Thomas
Complete VPO systems powered by Hauptwerk™. Real Wood Consoles, PC or MAC Computer Sound Modules, Audio for Home or Church.
info (at) organtechnology.com http://www.organtechnology.com

Authorized Hauptwerk Dealer; Milan Digital Audio Dealer..
User avatar
organtechnology
Member
 
Posts: 1753
Joined: Sun Aug 02, 2009 5:58 pm
Location: DFW, TX USA

Re: Wiring an Expression Pedal - question for electronic gur

Postby magnaton » Sat Feb 24, 2018 11:28 am

organtechnology wrote: Salvage the kick switch and maybe the pedal mechanism and build a slide potentiometer pedal out of plastic kitchen cutting board, toilet water level hardware, a slide potentiometer from spark fun.

Thomas


You'd be surprised how well this works! Be sure to add a small, cheap hinge at bottom. Here is what it would basically look like:

http://forum.hauptwerk.com/viewtopic.php?f=15&t=10400&p=76477&hilit=Ed%27s+pedal#p76477

Danny B.
User avatar
magnaton
Member
 
Posts: 343
Joined: Tue Feb 10, 2015 7:28 pm
Location: Austin, TX

Re: Wiring an Expression Pedal - question for electronic gur

Postby larason2 » Sun Feb 25, 2018 2:32 pm

I have a similar setup in my machine - a photoresistor and a light bulb with a metal plate separating them. I asked some friends of mine how I could hook it up to my midi board, and I was told I would first have to hook up the light bulb to a power source, which is tricky since the bulb is 24v. I was told to get the appropriate transformer, which are easily available, and connect the bulb to a potentiometer, then connect it to the transformer. Once that is done, connect the assembly to power at the highest resistance setting, then decrease the resistance until I get the amount of light I want. Then, replace the potentiometer with a resistor at the same resistance. This is to increase the lifespan of the circuit.

Then, the idea is to hook a multimeter in resistance mode to the photoresistor outputs to get an idea of how much resistance you are looking at at the maximum and minimum ends (with the pedal fully depressed and fully released). My friend said depending on the numbers, he would be able to help me wire an operational amplifier to decrease the gain in resistance to something more linear. Researching on the web, I have also seen talk of using a voltage divider to accomplish the same task, but I haven't been able to find an example of how to wire up a voltage divider to decrease the gain in resistance.

I haven't tried wiring it up my pedal yet, but it is on my to do list, and that is the approach I would take. Making a mechanical linkage with a linear potentiometer might be easier than above, but the downside is that potentiometers have a limited functional life. Pedals based on an optical sensor will potentially last longer, but more complex to wire.
larason2
Member
 
Posts: 30
Joined: Thu Feb 04, 2016 10:32 pm

Re: Wiring an Expression Pedal - question for electronic gur

Postby Grant_Youngman » Sun Feb 25, 2018 4:04 pm

larason2 wrote:
I haven't tried wiring it up my pedal yet, but it is on my to do list, and that is the approach I would take. Making a mechanical linkage with a linear potentiometer might be easier than above, but the downside is that potentiometers have a limited functional life. Pedals based on an optical sensor will potentially last longer, but more complex to wire.


There are certainly applications where an LDR makes sense. I'm highly skeptical of this one — since the objective is to provide a linear resistance change vs. pedal position to a MIDI CC controller input. It's one thing if the LDR is being used directly in an analog audio circuit to control a gain stage where a sort of logarithmic response is good, or as a light-no-light sensor, but this is a different application. I think a better solution in the long run is a high quality linear actuation potentiometer or a different expression pedal altogether that can control a (similarly high quality and sealed) rotational potentiometer. You avoid all of the issues of attempting to linearize something that has a nonlinear native resistance of maybe 10K to 600K ohms, multiple power supplies if bulbs require 24 volts, or figuring out how to change the bulb to an appropriate LED with a color temperature that matches the sensor, etc. A 10K linear pot is a far simpler and likely less troublesome solution.
Grant
User avatar
Grant_Youngman
Member
 
Posts: 970
Joined: Sat Jan 20, 2007 7:50 pm
Location: Savannah, Ga

Re: Wiring an Expression Pedal - question for electronic gur

Postby engrssc » Sun Feb 25, 2018 4:15 pm

RE a variable voltage source, something like this is a good choice

https://www.ebay.com/itm/3-5-30V-to-4-30V-DC-DC-Booster-Convert-Step-Up-Voltage-Regulator-LM2587-T9/332526504225?epid=18007435243&hash=item4d6c1fc921:g:GD0AAOSwRE5aYs7I

A range of input voltages and variable output (voltages). You can do 12 VDC in and 24 VDC or whatever out. You can get cheaper DC to DC boosters (basically the same board from off shore sources for much less. Something like a $1 or so if you can wait for slow (month or more) shipping.

https://www.ebay.com/itm/263434043915?vectorid=229466&lgeo=1&item=263434043915&rmvSB=true

Aside from that, I agree with Grant. and wouldn't suggest using a LDR either. They are not meant to drive a MIDI encoder.

As far as using a slide type (linear) pot, I've had my 3 (2 swell, 1 crescendo) for a little over 10 years with no issues, using a pot encoder from Roman Sowa. Something like this would work The encoder I have (POT 32) isn't made anymore.

https://www.midi-hardware.com/index.php?section=prod_info&product=PDS&R2=USD

This board scans 32 - inputs in 4 X 8 matrix configuration for a pedal board) in addition to 3 potentiometer or external voltages It has user defined update rate and resolution of the pot inputs. Esp useful on a theatre organ (like my Rodgers 340) as the swell peds are "exercised" probably more than on a classical instrument.

When I bought the slider pots (from Mouser) I bought 3 extra, just in case. They are still in the plastic bag they came in. It does pay to buy good ones. 8)

Basic advice, keep it simple, as in the KISS principle. :roll:

Rgds,
Ed
User avatar
engrssc
Member
 
Posts: 5510
Joined: Mon Aug 22, 2005 11:12 pm
Location: Roscoe, IL, USA

Re: Wiring an Expression Pedal - question for electronic gur

Postby RichardW » Mon Mar 05, 2018 9:09 pm

Grant_Youngman wrote:... the objective is to provide a linear resistance change vs. pedal position to a MIDI CC controller input.


I had an Allen expression pedal which used a lamp and an LDR. To help with linearisation they changed the shape of the slot in the shutter that the pedal was connected to. So the light output varied non-linearly in relation to the pedal motion.

To my surprise, I could connect the LDR output straight into my Roland AX controller keyboard and it worked without any problem.

Regards,
Richard
User avatar
RichardW
Member
 
Posts: 766
Joined: Sun Oct 28, 2007 10:16 am
Location: UK


Return to Audio / MIDI interfacing

Who is online

Users browsing this forum: No registered users and 3 guests