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Pedal "position" indicator

Building organ consoles for use with Hauptwerk, adding MIDI to existing consoles, obtaining parts, ...

Pedal "position" indicator

Postby engrssc » Tue Aug 11, 2009 12:14 pm

Does anyone have any suggestions for connection of a crescendo position indicator? I'm using a POT32 http://midi-hardware.com/pot32.html

from Roman Sowa as a (pot to) MIDI controller. Works great on all virtual organs. What (I think) I need is something that Roman also suggests, namely a bar/dot LED graph indicator such as a LM3914 - Dot/Bar Display Driver
http://www.national.com/mpf/LM/LM3914.html

This chip has 10 segments which can be configured either bar or dot. Has a voltage input (0 to 5 VDC) and lights the segments progressively. I would have to configure some sort of driver that would follow the crescendo (pedal) 10K pot. I've never read the pot's output voltage, but I would assume it to be non linear as mechanically I have limited the travel some.

Any ideas? The idea being it's a guess as to where the crescendo pedal is positioned (unless full closed or full open). If I can get something working with the crescendo, I might just add the same indicators for the other 2 expression pedals as the circuit for them is the same as the crescendo, just different MIDI output. Standard on many organs such as Rodgers and Allen.

Rgds,
Ed
Last edited by engrssc on Tue Aug 25, 2009 8:43 am, edited 1 time in total.
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Re: Pedal "position" indicator

Postby NickNelson » Tue Aug 11, 2009 1:41 pm

engrssc wrote:I've never read the pot's output voltage, but I would assume it to be non linear as mechanically I have limited the travel some.


Assuming it's a linear potentiometer, limiting the mechanical travel will affect the end point voltages, but not the linearity.

I dare say there would be any number of whizzy digital solutions to this (and I can think of quite a few myself), but how about a
simple old-fashioned moving coil meter. You would need a variable resistance somewhere to adjust the meter's sensitivity and
(possibly) another to offset any non zero voltage at the pedals minimum setting.

Let us know the resistance of the pedal potentiometer, and the highest and lowest voltage output, and I'm sure I or someone else
can suggest a suitable and inexpensive circuit.

Nick
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Re: Pedal "position" indicator

Postby engrssc » Tue Aug 11, 2009 1:59 pm

Will check the pot's output voltage range shortly. There is no room for a meter type indicator, at least without some significant mods. The non linearity would be the result of the crank type mechanism, originally Rodgers, that I utilized. The pot itself is a linear 10K which presently drives the POT32.

Appreciate the thoughts,
Ed
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Re: Pedal "position" indicator

Postby gingercat » Tue Aug 11, 2009 2:20 pm

You could create something using an Arduino / Freeduino board for very little money. http://www.arduino.cc/ http://www.freeduino.org/ I'm planning on adding a MIDI driven display to my organ using one of these boxes, as unlike MIDIBox components, you can buy the core unit pre-assembled, then just need to upload the app to it via USB. For UK users, the cheapest I've found the boards is http://www.nuelectronics.com/estore/ Hopefully my board will end up being a display capable of MIDI input and output.
Regards,
Chris Blaylock
i5 4670k, 32GB RAM, Win7, 2xELO 1280x1024 Touchscreens, Focusrite Saffire, MIDISport 4x4
4 Manual Console, 32 R&C Pedalboard, 3xExpression, Solenoid coupler tabs
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Re: Pedal "position" indicator

Postby John D » Wed Aug 12, 2009 2:42 pm

Hi,

I am using the Artisan Micro Midi system. They have as an accessory a 4 line lcd panel that is programable. I have mine set to indicate the crescendo level and the two swell indicators. It also tells me the memory level, Transposer level wnad which of 5 sample sets is currently loaded. It is a very noce unit, and can be used with any midi organ
Dr. John R. Durgan
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Re: Pedal "position" indicator

Postby engrssc » Wed Aug 12, 2009 2:56 pm

Thanks, Dr John, for the info. Unfortunately, I don't have the Micro Midi system, but would be interested in being able to do some of the same things. I have heard of other drivers for an LCD display and know H/W implementrs such. For the moment, I would like to find a (simple) driver/interface for an LED chip as I mentioned above.

Rgds,
Ed
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Re: Pedal "position" indicator

Postby NickNelson » Thu Aug 13, 2009 1:09 pm

The LM3914 is about as simple a driver for a 10 led bar/dot display as you'll find.
I've not been able to locate (in the US or Europe) an obviously suitable pre-built
module, so I think you will have to construct it yourself.

I've played around wirh these before and they aren't difficult to use.

Nick
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Re: Pedal "position" indicator

Postby dalest » Thu Aug 13, 2009 1:53 pm

if someone can do it for me , i'm interessting too for the crescendo pedal and swell pedal
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Re: Pedal "position" indicator

Postby engrssc » Thu Aug 13, 2009 4:15 pm

LM3914 chips are available on eBay for $2.70 USD Buy Now or Best Offer with free shipping. You would need a socket and bezel of some sort to make it look good. Haven't found anyone offering a "package" yet.

Rgds,
Ed

Rgds,
Ed
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Re: Pedal "position" indicator

Postby engrssc » Thu Aug 13, 2009 8:10 pm

I should add a typical 10 segment LED display is on (bottom) of this page: http://www.futurlec.com/LEDDisp.shtml cost less than: $1.

Rgds,
Ed
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Re: Pedal "position" indicator

Postby NickNelson » Fri Aug 14, 2009 5:50 am

Here is a simple (and rather ugly) implementation of the LM3914 and a 10 segment LED bar, with the circuit, and apologies for the rather iffy images.

ImageImage

Notes:

The display is in 'dot' mode rather than 'bar' mode. This mean that the current drawn when a LED is on is
constant at about 20mA. For my own pedal board encoder, this means that the three wires can simply be connected to the expression potentiometer and the encoder will happily supply the necessary current. In 'bar' mode, with all 10 LEDs on the current drawn would exceed 100mA and overload the encoder. You would certainly need to check with the maker of your encoder whether this current (or indeed any current) can be drawn from the + end of the pot.

If the encoder can't provide the current, you would have to provide a separate supply (3V minimum, 25v maximum). This need not be particularly well regulated, and would probably allow 'bar' mode to be used, by connecting pin 9 to V+ (pin3).

The sensitivity of the circuit is set by the 100k and 33k resistors, and is independent of the supply voltage. Within reasonable limits, reducing the value of the 33k resistor will decrease the sensitivity (so a higher input voltage will be needed to turn the uppermost LED on) and increasing the resistance will increase the sensitivity.

In this simple circuit, the low end point is 0 volts and isn't adjustable. I think that inserting a (small) resistance between pin 4 and ground would raise the lower end point, but I haven't tried this.

I dare say I could produce PCBs for this application (and incorporate more user friendly end-point adjustments), but only on a very limited and non-commercial basis (since I hate making them!).

Nick
Last edited by NickNelson on Thu May 02, 2019 11:18 am, edited 2 times in total.
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Re: Pedal "position" indicator

Postby dalest » Fri Aug 14, 2009 5:56 am

wow ! thank you so much.
I would like to know how i can connect 2t of this to my pedals crescendo and expression? Is it simply or not.
isa green light possible (instead of red),

if yes, i 'll be interestinf for 2 products.

thank you

bye bye

ERIC
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Re: Pedal "position" indicator

Postby engrssc » Fri Aug 14, 2009 10:03 am

Nothing "iffy" about your post, Nick. That is the circuit I have been looking at as in my first post http://national.com/mpf/LM/LM3914.html I and possibly others would be interested in your PCB, tho, Nick. I used to roll my own, but haven't done so lately.

BTW/FYI, the LED color is determined by the particular LED bargraph display you use. Color are red, green and yellow.

I was wondering, in place of the 100K/33K resistors, if a pot (say possibly a 150K) would act as a range control so as to adjust the display to more accurately show the pedal position?

I'm still looking for a mount (bezel) for the bargraph(s) to dress it up and make mounting a bit more presentable.

One suggestion was sent to me, that is, in place of the small bargraph display, to use individual LED's which are easier to mount. I think the small bargraph display is neat and not such an attention getter plus I don't have a lot of room, esp for 3 such.

I might be wrong, but I was led (not LED) to believe that the LM3914 input is voltage driven vs current driven). If that were to be the case, the amount of current drawn from the pedal pot would be negligible. I stand to be corrected on that assumption, tho.

Another question that I haven't looked into, is there such a thing as a 20 pin socket that could be mounted 90 degrees with respect to a PCB? That would make for a very neat "package". As most everyone has done at one time, I could "jury rig" something no doubt.

Rgds,
Ed
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Re: Pedal "position" indicator

Postby NickNelson » Fri Aug 14, 2009 11:13 am

engrssc wrote:I was wondering, in place of the 100K/33K resistors, if a pot (say possibly a 150K) would act as a range control so as to adjust the display to more accurately show the pedal position?


Yes, that would work fine

I might be wrong, but I was led (not LED) to believe that the LM3914 input is voltage driven vs current driven). If that were to be the case, the amount of current drawn from the pedal pot would be negligible. I stand to be corrected on that assumption, tho.


You're right, the signal input to the LM3914 is very high impedance and wouldn't measurably load the wiper of a 10k potentiometer. The point I was trying to make was that one needed to
be careful where the current to drive the LED was taken from. The rather tempting assumption that a low impedance current source would be available from the 'hot' end of the potentiometer
wouldn't always be satisfied (nor that the other end would necessarily be grounded).

Another question that I haven't looked into, is there such a thing as a 20 pin socket that could be mounted 90 degrees with respect to a PCB? That would make for a very neat "package".


Yes, that would be nice. In fact there's one here: http://www.rapidonline.com/Cables-Connectors/Connectors-Multipole/DIL-Sockets/DIL-Display-sockets/63763 I'm ashamed I didn't think to
look for such a thing until prompted. All we need now are suitable bezels.

Nick
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Re: Pedal "position" indicator

Postby engrssc » Fri Aug 14, 2009 1:09 pm

Regarding a bezel(s), DigiKey has quite a few, but none the right size for a bar graph display. Mouser hasn't replied yet. I also inquired with an outfit that distributes bargraph displays, same answer, negative. We'll find one available at the last place we look. Looking into what some meters with digital bargraph use, but here too, not useful here.

Rgds,
Ed
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