Power amp trigger mod?

[jrhees]

OOOOOh, pretty picture

Just a note on your diagram, the SOIC orientation suggests you're connecting to pin 12, not pin 3...but you probably know that.

The reason I want you to connect to the USB's +5V connection rather than somewhere else is so that we don't create a situation where +5V is present somewhere else while the USB port has yet to power up -- thus forcing 5V onto a pin on a non-powered micro.

-Jon

[ElvisIncognito]

OOOOOh, pretty picture

I thought I may as well document it for those who may follow.

Just a note on your diagram, the SOIC orientation suggests you're connecting to pin 12, not pin 3...but you probably know that.

Actually, I didn't. I don't have much experience with SOICs (they're primarily used in PICs?) and was thus unsure of the proper symbol, so I drew it as an 18 pin DIP. But now I'm REALLY confused. If you're counting pins the way I think you are...

1-3-5-7--9-11-13-15-17
2-4-6-8-10-12-14-16-18 ?

then wouldn't that be pin 13? Or are you saying it's...

18-17-16-15-14-13-12-11-10
9---8---7---6--5---4--3---2---1 ?

I guess while we're at it, you should probably tell me how to properly identify pin 1. (I think it's fairly obvious, but I'd rather be safe than sorry.)

The reason I want you to connect to the USB's +5V connection rather than somewhere else is so that we don't create a situation where +5V is present somewhere else while the USB port has yet to power up -- thus forcing 5V onto a pin on a non-powered micro.

OK. I just remembered previous statements you made (when discussing external emitters) where you mentioned current limitations and I was trying to circumvent those. Would it be correct to say that connecting the USB-UIRT to a powered hub might resolve such issues (as well as any impact that this little mod may have)? Or will this mod have no impact? (i.e. is the emitter issue related to a limitation of the USB-UIRT as opposed to being a USB supply issue?)

[jrhees]

YIKES!

Your method of numbering pins on an IC is not correct!

ALL dual-row IC's are numbered in a circular fashion. Pin 1 is indicated with a dot or 'hole' in the IC on one end or corner.

So, for the SOIC:

1 1 1 1 1 1 1 1 1
8 7 6 5 4 3 2 1 0
-------------------
| |
|o |
-------------------
1 2 3 4 5 6 7 8 9

As far as the power draw, I don't think an extra 20mA (the relay coild current) is going to pose a problem...

-Jon

[ElvisIncognito]

YIKES!

Your method of numbering pins on an IC is not correct!

ALL dual-row IC's are numbered in a circular fashion.

LOL! I know how DIPs are typically numbered, Jon, and that's the way I had it in the first place. (Spin your drawing 180 degrees and you have the same thing I had!)

Pin 1 is generally shown at the upper right in basic diagrams, so when you told me I had pin 12 connected, I thought that maybe SOICs had some kind of wacky numbering scheme. (I should have guessed we were simply 180 degrees out of phase, but again, I've had very little (no) exposure to SOICs.)

[epatsellis]

John, is it possible to add a small header, with the # of extra i/o's available, ULN-5804's (?) are pretty cheap and will sink quite a bit of current.

erie

[jrhees]

Erie,

There's really not enough room on the existing PCB to fit a header. Because this is only of interest to a select few, I still think the best way to handle this is DIY-style, so as not to add *any* cost to the base design.

Also, there really *aren't* any available I/O's -- the one we're using in this case is really intended for another feature, but we're 'cheating'.

-Jon

[epatsellis]

that's probably best approach then, I guess there's still a few of us that remember how to solder 30 ga. wirewrap wire...

erie(former electronics weenie)

[ElvisIncognito]

Jon-

I'm ready to go on this... when will you have the firmware update to support it?

[jrhees]

ElvisIncognito,

No firmware update needed...but I need to post a test Girder plugin. I'll try to get something posted today and I'll let you know...

-Jon