SAMS and PTC Thermistors

[Les Knoll]

First of all, if your SAMS do not draw over .5 amp, for the most part, you are safe as far as the ULN chips go because the chips are designed to output 1/2 amp continuously to a single output, just not necessarily ALL of them at once on the same chip for prolonged periods.

Secondly if a ULN chip DOES fail, you want to know about it AND FAST! Often their failures result in turning the chips into what are called 4 layer devices. The result is a nearly DIRECT SHORT from high current supply voltage to ground. You get the whole 'smoke show', heat, smoke AND FLAMES!  I have had it happen, this is no made up story!

If this 3.x combination action system has this known flaw with sticking SAMS which can conceivebly lead to ULN failure and the 4 layer failure modes mentioned above, I would not consider it a fully functional design.

I have published enough information on how my system in 2.4 works so that it could be built by others, they have told me so. It has been working without a hitch for nearly 6 months now and I play the daylights out of the instrument on a nightly basis. I HAVE had sticking SAMS (they are all over 30 years old) and the only problem  has been that they would not go up or down as requested by the piston. I let go of the piston, no more current, end of story. It is a mechanical problem on the SAM only, preciesely as on pipe organ systems, and is fixed just as easily.

My point is NOT to brag about my system, but to humbly suggest that the methodology and algorythms I have employed in my 'old school' 2.4 system be emulated in a version 3.x system. I am not versed in 3.x, so would not have the credentials to do such a conversion.

Take it from one who has blown up a few boards in his time, do not commit big hardware $$$ to a system until you know it is proven.

When considering SAMS driver systems (driver boards) PLEASE consider that some of the older SAMS, especially the Reisner and Allen units (without reed switches), have the driver commons and the stop switch common BOTH sttached to the unit's frame. This means that the stop switch outout is the same source and polarity as the common of the source used to drive the SAMS. Usually this is no problem since the signals from the stop switches are usually positive anyway. Some type of interface is usually necessary for these type of SAMS.  I use ittyMIDI decoders on everything and these require a do-it-yourself diode matrix. A simple optoisolator + resistor interface for each stop (also acts as its own diode for the matrix) does the trick. For those that use the voltage-to-MIDI note decoders (MUCH more expensive) this work is fortunately already done for you.


     

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[dvtutlo]

Les and all,
There are design rules that engineers use that control the safety and the correctness and
adherence to the user requirements for hardware design of these boards.

The ULN chips look ok for 0.5amps BUT if you get flames -- it's no good.

So ABOVE the hardware design part of the tree, there's the organist's requirements.  The
organist is the originator with wants and desires of how their organ should work. These
requirements do not include --"oh I need 3 flutes, 3 strings and 2 horns on the great-- oh
wait, I can't put them all on because they are on the same chip."

Who cares about the chip, that's down at the hardware design level.
So I don't belive it should have anything to do with what version of jOrgan you have. There
should never be burn outs.

If the engineer used a ULN chip that provides all those inputs, then all these inputs could
happen. So if the chip can't handle all 8 on at the same time, you (the engineers) should
never use all 8 inputs. BECAUSE the organist could select as many SAMs as they want and
for the engineer that should mean ONE STOP or ALL STOPS SIMULTANEOUSLY.  That's
the hardware design criteria!

To avoid these problems (and assuming your SAMs are 1/2 amp stops) I would say if the
organist wants to use these boards, they should only use i.e. wire-up only the number of
inputs on each chip that would not exceed the power dissipation of the chip. (THAT MEANS
YOU CAN'T USE ALL OF THE INPUTS FOR EACH CHIP) This means you will use more
boards. But then you will be able to use any number of stops you want without regard to
worrying about -- "what if one or two stops stick?"

Remember, if you have say an Allen organ, many of their models even the older ones have
bidirectional drivers right on the SAMs. So you won't need the ULN chips and/or the
associated boards, you just need TTL signals from your preset memory to go to each SAM.

This is not a scientific paper just some input on this problem. I hope this was helpful.
Dave







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[svenmeier]

Hi all,

just for the record:
I'm currently investigating if combination actions can behave like
switches. This might give us more possibilities for SAM control (and
might even be a solution to lighted-up pistons).

Stay tuned

Sven

Les Knoll schrieb:

> First of all, if your SAMS do not draw over .5 amp, for the most part, you are safe as far as the ULN chips go because the chips are designed to output 1/2 amp continuously to a single output, just not necessarily ALL of them at once on the same chip for prolonged periods.
>
> Secondly if a ULN chip DOES fail, you want to know about it AND FAST! Often their failures result in turning the chips into what are called 4 layer devices. The result is a nearly DIRECT SHORT from high current supply voltage to ground. You get the whole 'smoke show', heat, smoke AND FLAMES!  I have had it happen, this is no made up story!
>
> If this 3.x combination action system has this known flaw with sticking SAMS which can conceivebly lead to ULN failure and the 4 layer failure modes mentioned above, I would not consider it a fully functional design.
>
> I have published enough information on how my system in 2.4 works so that it could be built by others, they have told me so. It has been working without a hitch for nearly 6 months now and I play the daylights out of the instrument on a nightly basis. I HAVE had sticking SAMS (they are all over 30 years old) and the only problem  has been that they would not go up or down as requested by the piston. I let go of the piston, no more current, end of story. It is a mechanical problem on the SAM only, preciesely as on pipe organ systems, and is fixed just as easily.
>
> My point is NOT to brag about my system, but to humbly suggest that the methodology and algorythms I have employed in my 'old school' 2.4 system be emulated in a version 3.x system. I am not versed in 3.x, so would not have the credentials to do such a conversion.
>
> Take it from one who has blown up a few boards in his time, do not commit big hardware $$$ to a system until you know it is proven.
>
> When considering SAMS driver systems (driver boards) PLEASE consider that some of the older SAMS, especially the Reisner and Allen units (without reed switches), have the driver commons and the stop switch common BOTH sttached to the unit's frame. This means that the stop switch outout is the same source and polarity as the common of the source used to drive the SAMS. Usually this is no problem since the signals from the stop switches are usually positive anyway. Some type of interface is usually necessary for these type of SAMS.  I use ittyMIDI decoders on everything and these require a do-it-yourself diode matrix. A simple optoisolator + resistor interface for each stop (also acts as its own diode for the matrix) does the trick. For those that use the voltage-to-MIDI note decoders (MUCH more expensive) this work is fortunately already done for you.
>
>
>      
>
> -------------------------------------------------------------------------
> Check out the new SourceForge.net Marketplace.
> It's the best place to buy or sell services for
> just about anything Open Source.
> http://sourceforge.net/services/buy/index.php
> _______________________________________________
> jOrgan-user mailing list
> jOrgan-user@...
> https://lists.sourceforge.net/lists/listinfo/jorgan-user
>
>  

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[Roy Radford]

Hi, Dave,

 

           Well my input to this problem would have to be;

 

    The ULN chip is perfectly capable of handling its full complement of channels unless a magnet sticks. In that case, surely the correct solution is not to massively derate the capabilities of the chip, but to disconnect the offending magnet, ie put a PTC thermistor in series with it. Even allocating one ULN per magnet won't stop the coil burning out if it sticks. The PTC solution cures the problem where it arises.

 

      Just my two penn'orth!

 

           Have fun,

 

              Roy.

 

  PS... Anyone for barbequed SAMs?  

--- On Fri, 6/6/08, dvtutlo@... <dvtutlo@...> wrote:

From: dvtutlo@... <dvtutlo@...>
Subject: Re: [jOrgan-user] SAMS and PTC Thermistors
To: jorgan-user@...
Date: Friday, 6 June, 2008, 3:51 PM

Les and all,
There are design rules that engineers use that control the safety and the
correctness and 
adherence to the user requirements for hardware design of these boards.

The ULN chips look ok for 0.5amps BUT if you get flames -- it's no good.

So ABOVE the hardware design part of the tree, there's the organist's
requirements.  The 
organist is the originator with wants and desires of how their organ should
work. These 
requirements do not include --"oh I need 3 flutes, 3 strings and 2 horns
on the great-- oh 
wait, I can't put them all on because they are on the same chip."

Who cares about the chip, that's down at the hardware design level.
So I don't belive it should have anything to do with what version of jOrgan
you have. There 
should never be burn outs.

If the engineer used a ULN chip that provides all those inputs, then all these
inputs could 
happen. So if the chip can't handle all 8 on at the same time, you (the
engineers) should 
never use all 8 inputs. BECAUSE the organist could select as many SAMs as they
want and 
for the engineer that should mean ONE STOP or ALL STOPS SIMULTANEOUSLY. 
That's 
the hardware design criteria!

To avoid these problems (and assuming your SAMs are 1/2 amp stops) I would say
if the 
organist wants to use these boards, they should only use i.e. wire-up only the
number of 
inputs on each chip that would not exceed the power dissipation of the chip.
(THAT MEANS 
YOU CAN'T USE ALL OF THE INPUTS FOR EACH CHIP) This means you will use more

boards. But then you will be able to use any number of stops you want without
regard to 
worrying about -- "what if one or two stops stick?"

Remember, if you have say an Allen organ, many of their models even the older
ones have 
bidirectional drivers right on the SAMs. So you won't need the ULN chips
and/or the 
associated boards, you just need TTL signals from your preset memory to go to
each SAM.

This is not a scientific paper just some input on this problem. I hope this was
helpful.
Dave







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