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  #1  
Old 06-09-2010, 04:42 PM
E.Cado E.Cado is offline
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Default MSA-T Solenoid help for newbies?

Hey guys!

My friend and I have started building a little MIDI triggered solenoid drummer robot and we are having some trouble.

Our MSA-T arrived a few weeks ago and we decided to just rig up a simple circuit to try and see if we could get a single solenoid firing before we housed everything in a more permanent way and set up the other two solenoids.

Well we have got the MIDI coming into the MSA-T without a problem and have both LED's glowing. However the solenoid's aren't firing and i'm 99% sure the MIDI messages are configured properly.

We both started this project with close to nil electronics experience so there may be something glaringly obvious missing.

We have got some little 6V PCB solenoids we were hoping to run straight from the MSA-T board without the need for an external solenoid power supply because according to the documentation the MSA-T has 24V Max Switching Voltage for its outputs. Does this mean that the board should be able to power our three 6V PCB solenoids? (6+6+6 = 18V) Or have I miss-interpreted the terms and we do infact need an external power source for the solenoids?

We tested the outputs of the MSA-T at various points between the output and the single solenoid that we hooked up which should have been firing from the MIDI being sent to it with a multimeter and got a very small reading of about 0.16 V. Can someone please explain to us why we are getting such a tiny voltage out of the outputs? Have we missed something very obvious?

Attached is a simple (unprofessional) circuit diagram and a photo of our simple circuit (though it isn't all hooked up in the photo).

Cheers,
Ryan
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Old 06-09-2010, 06:59 PM
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John John is offline
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Hi Ryan,

The MSA-T outputs are "pulled down to ground" when they are activated. Ground = 0V. When the outputs are off, they "float", which means that they behave like they are not connected to anything.

So, you'll need to arrange your circuit so that a positive voltage flows through the solenoid and into the MSA-T output.

In your diagram, it looks like the positive leads of the solenoids, instead of being connected to a positive voltage, are connected to ground--so no current will flow through them.

So, instead of connecting them to the power out "G" terminal, you could connect them to the "+" terminal and I think your test will succeed.

There are some caveats, however. You'll need to calculate how much current is drawn by the solenoid and make sure too much current doesn't flow into the MSA-T output.

Since you're using the MSA-T 5V output (Power "out" terminals), you'll also need to be sure that all of the solenoids combined won't draw too much current from the MSA.

"Too much" is described in the MSA-T hardware user manual. See the power supply specifications and the electrical specifications.

For basic info about voltage, current, etc, check out:

http://www.kpsec.freeuk.com/study.htm

A little reading about the basics will save you a lot of time and headaches as you work on your project, and also make it less likely that you'll damage a component, MIDI board, etc.

Hope this helps.
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Old 06-10-2010, 04:32 AM
E.Cado E.Cado is offline
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Thanks for the reply John!

I'll give that a go and let you know.

I remembered enough from high school physics to think to do some calculations before we started building to check that the current fit the board's specs.

Using (P= I x V):

The solenoids are rated to 1.5 Watts each.

1.5 W = I x 6V

so the current draw of each solenoid = 250 mA

From my understanding, the circuit is parallel, so the current draw of each solenoid will be compounded, correct? So 750mA all up if 3 solenoids are firing which is too much for the boards 250mA Max Sink Current?

The board should be able to handle the draw from one solenoid so we'll start from there and try and get it working.

Cheers,
Ryan

Edit: Just switched the Ground to the + terminal and success on a single solenoid firing

Last edited by E.Cado; 06-10-2010 at 06:38 AM.
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Old 06-10-2010, 06:03 PM
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John John is offline
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Quote:
Originally Posted by E.Cado View Post
so the current draw of each solenoid = 250 mA

From my understanding, the circuit is parallel, so the current draw of each solenoid will be compounded, correct? So 750mA all up if 3 solenoids are firing which is too much for the boards 250mA Max Sink Current?
Each MSA-T output can handle the 250mA, yes. Even if 3 solenoids are simultaneously activated, the load is 250mA from each of 3 MSA-T outputs, which is fine.

However, since you're using the MSA regulated 5V output to supply power to the solenoids, it will be supplying 750mA. This is enough to heat up the voltage regulator (IC3). You may have to add a heat sink to the regulator.

It's also possible that the MSA will "brown out" for a split second when the solenoids are fired. If this happens (you'll be able to tell, because the MSA will reset) you'll have to switch to a separate solenoid power supply. But this may not be a problem.

I hope you'll post some photos or video of the robot drummer!
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Old 06-27-2011, 09:18 AM
E.Cado E.Cado is offline
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Hey guys! its been a while.

Thought i'd drop in and post up where our project is at at the moment.

http://www.youtube.com/watch?v=-8AZ7_tnd0E

We've got the MSAT running the chopsticks and a J-Omega MIDI servo controller on the drumsticks. The servos are way noisy and too slow which stops the xylophone keys resonating well but we hope to fix this sometime in the future.

Cheers
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Old 06-27-2011, 03:58 PM
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Quote:
Originally Posted by E.Cado View Post
Hey guys! its been a while.

Thought i'd drop in and post up where our project is at at the moment.

http://www.youtube.com/watch?v=-8AZ7_tnd0E

We've got the MSAT running the chopsticks and a J-Omega MIDI servo controller on the drumsticks. The servos are way noisy and too slow which stops the xylophone keys resonating well but we hope to fix this sometime in the future.

Cheers
Ryan, thanks for the update and for the video. Let me humbly suggest the MD24 for anyone considering MIDI servo control.
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