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Old 03-07-2013, 07:35 PM
theFlaneur theFlaneur is offline
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Default A Variety of questions...

I have a project that will require a few different products: the MIDI CPU and at least a pair of MSA-R boards. What I'd like to know is:

1. Does each board require a dedicated power source or can a single power source be used to daisy chain the boards? I'd need them all to be battery powered in a confined space so ideally I could use a singly 9V battery to power all three. If that's possible my only concern is battery life, would I need to replace batteries often?

2. I saw in the forum that the Logic outputs on the MPA can be configured to activate external relays. I don't really have a need for the MPAs digital pots and was wondering if either the MIDI CPU or MSA-R have this capability. I need to be able to activate at least 2 DPDT Reed Relays and possibly an SPDT as well.

3. I plan on using a rotary encoder with a 7-segment LED display on the CPU. Pardon my lack of knowledge, but is it possible to configure the CPU to display letters (in addition to numbers) on the LED? Is there a limit to how many characters the LED can display? Ideally I'd like to have up to 9 characters displayed at a time.

Many thanks!
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Old 03-07-2013, 07:58 PM
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John John is offline
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Hi theFlaneur, welcome to the forum.

Quote:
Originally Posted by theFlaneur View Post
I have a project that will require a few different products: the MIDI CPU and at least a pair of MSA-R boards. What I'd like to know is:

1. Does each board require a dedicated power source or can a single power source be used to daisy chain the boards? I'd need them all to be battery powered in a confined space so ideally I could use a singly 9V battery to power all three. If that's possible my only concern is battery life, would I need to replace batteries often?
Yes, you can connect the power input of each board and attach them in parallel.

The battery life will depend greatly on the amount of activity. For example, an MSA-R with all 8 outputs "on" will drain the battery much faster than an MSA-R with all 8 outputs "off".

The only way to really know the exact battery life will be by timing it under normal operating conditions.

Quote:
2. I saw in the forum that the Logic outputs on the MPA can be configured to activate external relays. I don't really have a need for the MPAs digital pots and was wondering if either the MIDI CPU or MSA-R have this capability. I need to be able to activate at least 2 DPDT Reed Relays and possibly an SPDT as well.
Yes, the MSA-R relays can in turn activate larger secondary relays. If using external relays is the primary application, the MSA-T is the best choice. (See this thread for a wiring example.)

Quote:
3. I plan on using a rotary encoder with a 7-segment LED display on the CPU. Pardon my lack of knowledge, but is it possible to configure the CPU to display letters (in addition to numbers) on the LED? Is there a limit to how many characters the LED can display? Ideally I'd like to have up to 9 characters displayed at a time.
The MIDI CPU doesn't support letters as 7-segment output, only numerals. Sorry. If you'd like to describe in more detail what type of information you'd like to display, I might be able to provide some info that is a little more useful.

I hope this helps. Please let me know if I can provide more information.
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Old 03-07-2013, 08:52 PM
theFlaneur theFlaneur is offline
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Thanks for the prompt reply, John!

Definitely helpful. Although I just remembered I may have a use for an MPA board after all. Quick question about that though...

To achieve a higher resistance than 100k I know that you can chain digital pots together. Is there any fancy math to this, or is it as simple as 1pot + 1pot = 200k? I figured I'd ask first instead of assume it would be so intuitive... not always the case with these things. ;-)

If it is that simple, am I limited to resistance values in 100k increments? What if I wanted to have 250k resistance?
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Old 03-07-2013, 11:36 PM
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John John is offline
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Quote:
Originally Posted by theFlaneur View Post
Thanks for the prompt reply, John!

Definitely helpful. Although I just remembered I may have a use for an MPA board after all. Quick question about that though...

To achieve a higher resistance than 100k I know that you can chain digital pots together. Is there any fancy math to this, or is it as simple as 1pot + 1pot = 200k? I figured I'd ask first instead of assume it would be so intuitive... not always the case with these things. ;-)

If it is that simple, am I limited to resistance values in 100k increments? What if I wanted to have 250k resistance?
Good questions.

If you need just a variable resistance (two terminals), then the math is simple. Just add the resistances in series to get the resistance value that you want.

If you are using the pots as 3-terminal voltage dividers, things get more complicated.

Once you start to consider how potentiometers work, you will notice that it's much easier to reduce the effective value of a pot than to increase it.

There are some things you can do, like add a series fixed resistance to the terminals. But the result may not be exactly what you need.

Unfortunately, for the digipots on the MPA, 100k is the largest value available from the manufacturer.

It is also worth noting that the tolerances on the digipots are very loose at around +/- 30%.

The bottom line is: expect to do some experimenting with resistance values before you get the exact result that you need.
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Old 03-07-2013, 11:39 PM
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If you care to post a project thread in the MPA forum, I'd be happy to discuss some strategies for getting larger effective values.
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