MSA-R vs MSA-T

[lotan]

Hi!

Nice to have a forum, hope people will use it more and more...
I bought a MSA-R and a MSA-T but finally, I'm not sure I'm fully understand the difference... They seems to do the same things, am I wrong?

Thanks!

[John]

Hi lotan, great question--this one is asked quite frequently.

The MSA-R has SPST reed relay outputs, which are just like an SPST switch (see web for SPST definition :)). In other words--each MSA-R output is like a simple toggle or pushbutton switch, except that it is controlled by an electrical impulse, instead of your finger. When the output is "on", the "A" output terminal is connected to the "B" output terminal by the relay. Since the relay operates via a magnetic field, each output is electrically isolated (completely disconnected) from the rest of the MSA circuitry.

The MSA-T has NPN Darlington Transistor outputs. These are also used for "switching" purposes, but they are not the same as a mechanical switch. To see how an NPN transistor is used for switching, see "Using a transistor as a switch" on this page:

http://www.kpsec.freeuk.com/trancirc.htm#switching

...so, on the MSA-T, the collector ("C") lead of the on-board transistor is connected to the "A" output terminal. When the output is "off", the terminal is left "floating" (as if it were disconnected)--so no current flows through it. When the output is "on", the terminal is "pulled down" (effectively, connected) to MSA ground, which causes current to flow through the load. There is an application circuit diagram in the MSA-T hardware user manual.

The page from above also has a nice summary of reasons to use a relay (MSA-R) or a transistor (MSA-T) for switching. See "When to use a relay":

http://www.kpsec.freeuk.com/trancirc.htm#relays

...but the electrical specifications for each MSA model must be considered as well.

Was this helpful? You might read the entire page linked above, to really get a good feel for everything.

By the way, the MSA-P is just like the MSA-R, except that it uses a type of solid-state relay (no moving parts) rather than reed relays.

[GoatBoy]

:)Just finished putting one of these babies together and noticed a forum for it!
It says in the link that reed relays aren't as quick as transistors for quick switching! I'm going to be using it to control solenoids for a musical project similar to the Drumbot project in Make. In fact that's why I bought it! Is it possibly the wrong choice? I'm also experimenting with Arduino and the Miditron.

[John]

:)Just finished putting one of these babies together and noticed a forum for it!
It says in the link that reed relays aren't as quick as transistors for quick switching! I'm going to be using it to control solenoids for a musical project similar to the Drumbot project in Make.

Yes, transistor switching is faster than relay switching. But the relays on the MSA-R have a switching delay of only about 1ms (0.001 second). So the MSA-R will work fine. ;) By the way, this type of info is included in the hardware user manual.

Let me know if you have other questions. I hope you'll post your project online.

[GoatBoy]

Thanks for your reply John! It would seem to me in retrospect that apart from having to wire up a little protection circuit, that the MD24 offers a lot more for your buck! 3 times the amount of outputs and PWM to boot as well as being cheaper! Is there any disadvantages I may have missed? Also will you create any decoders that offer input for connecting sensors and the like? This is something that I'm very interested in and forgive me for posting all od this in the wrong place!!

[John]

Thanks for your reply John! It would seem to me in retrospect that apart from having to wire up a little protection circuit, that the MD24 offers a lot more for your buck! 3 times the amount of outputs and PWM to boot as well as being cheaper! Is there any disadvantages I may have missed?

The MD24 does have 3x the outputs. The difference is that they are 5V logic outputs rather than relays or transistors. So it just depends on the application. Some users need relays, and prefer having them built into the board. For users who plan only to control other 5V logic circuits, the MD24 is better.

Of course, one can also control relays with the MD24, but you'll need to add extra circuitry between the MD24 and the relay. See this thread:

http://forum.highlyliquid.com/showthread.php?p=3#post3

Driving a relay coil with the MD24 is just like driving a solenoid, etc.

Also will you create any decoders that offer input for connecting sensors and the like? This is something that I'm very interested in and forgive me for posting all od this in the wrong place!!

Yes, there is such a product in development. It will generate MIDI messages in response to a variety of input types. This not a MIDI decoder, but rather a MIDI encoder, aka MIDI controller. Please keep an eye on the blog for an announcement. :)

[GoatBoy]

Thanks for all of that John! Understood and appreciated! I forgot to mention that when putting together the MSA-R last night that in the hardware manuel there is no mention of IC-4, only 1,2 and 3! Wasn't a problem but something I'm sure you want to know. Thanks

[John]

Thanks for all of that John! Understood and appreciated! I forgot to mention that when putting together the MSA-R last night that in the hardware manuel there is no mention of IC-4, only 1,2 and 3! Wasn't a problem but something I'm sure you want to know. Thanks

Thank you. :) :) (fixed)

[joesuspense]

I purchased an MSA-R also to do something similar to the drumbot project in Make, but I've run into an issue. There seems to be an inrush of current when the relay opens and fires the solenoid that is causing the relay to "stick" open. would the MSA-T have been a better choice for firing solenoids?

I should mention that I'm using a 12v 1A power supply and solenoid rated for 24v and (I think) 300mA draw.

[John]

I purchased an MSA-R also to do something similar to the drumbot project in Make, but I've run into an issue. There seems to be an inrush of current when the relay opens and fires the solenoid that is causing the relay to "stick" open. would the MSA-T have been a better choice for firing solenoids?

I should mention that I'm using a 12v 1A power supply and solenoid rated for 24v and (I think) 300mA draw.

You're most likely correct about the inrush current. The MSA-T is typically better for DC loads such as a solenoid. However, MSA-T outputs are only rated for 250mA each...so you'd need to build a drive circuit regardless.

The best solution would probably be to build a solenoid drive circuit with a transistor as shown here:

http://www.kpsec.freeuk.com/trancirc.htm#switching

...and then drive it with the 5V output from the MD24 kit. But the MSA-R could also be used to drive the circuit. You could use the relay output or you could access the 5V control signals from R0-R7. Sort of like what is described in this thread:

http://forum.highlyliquid.com/showthread.php?t=34

...except that you'll be driving your NPN transistor rather than an LED.

Hope this helps.

[joesuspense]

Thanks John, that's exactly what I was looking for. One thing I'm not clear on. You said:

But the MSA-R could also be used to drive the circuit. You could use the relay output or you could access the 5V control signals from R0-R7.

I understand using the 5v control signals from R0-R7. Can you explain how I could use the relay output? Thanks again, I appreciate all the help!

[John]

Thanks John, that's exactly what I was looking for. One thing I'm not clear on. You said:

I understand using the 5v control signals from R0-R7. Can you explain how I could use the relay output? Thanks again, I appreciate all the help!

The circuit under the heading "Testing in a simple switching circuit" shows how a switch is used to control the NPN transistor circuit. You'd simply substitute the MSA-R control terminal pair for the switch in the diagram.

http://www.kpsec.freeuk.com/components/tran.htm#testing

[joesuspense]

I've ordered an MD24 to use the 5V pins to fire transistors as switches, but haven't assembled it yet. I attempted a couple of tests with the 5V from the MSA-R.

I've tested using the 5v power from the relay to fire a TIP120 with the LED circuit at:
http://www.kpsec.freeuk.com/components/tran.htm#testing

I used 1 9v to power the MSA-R and another for the LED circuit. This worked great.

I then tested using the TIP120 to switch the solenoid and wasn't successful. It didn't seem to switch at all. I was hoping somebody may be able to lend some advice. Attached is a schematic of what I tried.

I'm using a 9V battery to power the MSA-R
I'm using a 12V/1A DC wall wart for the solenoid
I've put an IN4004 protection diode across the pins of the solenoid
The solenoid is a 24v 3.3-4.2 ohm coil.
http://www.goldmine-elec-products.com/prodinfo.asp?number=G16036
I've connected the ground from the wallwart and the ground from MSA-R (I could only get the LED test to work properly if the ground from both circuits)

I'm not sure what the base resistor value should be but, I've tried all different values. I tried to calculate what it actually should be and came up with 349ohm, so I tried 330ohm. That didn't work, so I randomly tried different values higher and lower without success.

Can anybody lend any guidance? Thanks in advance!!!

[John]

I'm using a 12V/1A DC wall wart for the solenoid
I've put an IN4004 protection diode across the pins of the solenoid
The solenoid is a 24v 3.3-4.2 ohm coil.


Ok...this is the first thing that jumps out. At 12V, a 4ohm coil will draw 3A. (4A, if the resistance is closer to 3ohms)

Current = Voltage / Resistance
I = V/R

12V / 4ohm = 3A

...so the wall wart may not be able to source the current needed to activate the solenoid. You need to get a power supply rated for 4A at minimum (probably more, to be on the safe side).

Then you should connect the power supply with a simple switch, to make sure it can fire... Once that's working, then you can add in the switching circuitry.

4A is a lot of current--make sure all of your wiring and components can handle the load. ;)

[joesuspense]

Thanks for the reply John.

I have tested the solenoid with the 12v/1A wall wart and it fires fine with a basic switch. It even fires well with the relays on the MSA-R when they don't stick. Does this make any difference?

[joesuspense]

Doh! Looks like I had things working. I fired up the circuit on the breadboard again, and it works perfectly. I think I may have had a flakey ground connection.

Thanks for all the help. I know this is out of the scope of supporting the MSA-R, so all the help is much appreciated.