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241  Using Arduino / General Electronics / Re: Preventing PCB interference on: January 09, 2013, 03:53:29 pm
The "star" grounding scheme looks good on paper, but quickly falls apart in real-world implementation, especially when doing complex PCB design. 
(Now, if you're doing point-to-point wiring, yeah, star-grounding is your friend. But we're not building vacuum tube amps here.)

I've had designs that called for separate analog and digital grounds but in the end, I just combined them all and made judicious use of ground planes on both top and bottom layer. Even amplifying weak analog signals 2000x voltage gain, there's no noise in the system (even with several relays being energized, SPI, etc running on the board.)

It also helps to confine analog and digital circuitry on their own sections of the board (if using a single board).... maybe even design it so it's two separate sections, (each with their own ground plane), and separated from each other by "moating" and just connect the grounds at a single point.

Another option is use (2) boards, and separate your logic board from the driver board. Just connect both boards with a ribbon cable. Distance is also your friend.

242  Using Arduino / General Electronics / Re: Making your own PCBs on: January 08, 2013, 10:14:36 pm
1) Does using skillet reflow create any fumes?  This is how I would be soldering my components b/c using a wand makes fumes.
Visible fumes? Not much... but you can smell it as the flux evaporates.  (depending on the solder paste you used, there may be some fumes.) These won't trigger the fire alarm.

2) Does drilling holes in a PCB with a Dremel make any fumes?
No, but depending on the number of holes you're drilling, you can create a lot of dust... and PCB dust has a distinct smell.

3) Does using etching solution or ironing the traces onto the board create any fumes?
No fumes. Now with etching, assuming you're using Ferric Chloride, you may not just be able to dump them in the sink without getting in trouble. ... if you drip/drop the FeCl, it will also cause stains. 
243  Using Arduino / Project Guidance / USBasp on: January 08, 2013, 10:04:27 pm
Anybody here using USBasp to program their chips under Mac OSX?

I bought a USBasp programmer (from China) and OSX doesn't seem to recognize it properly. It's not appearing in the Arduino IDE, and while system info shows it present under About this Mac, it's showing as "Unknown (device has not been configured)"
244  Using Arduino / General Electronics / Re: Newbie question on designing your own 'board' instead of using wires on: January 08, 2013, 02:41:46 am
Well, that's freaking news to me. I've always used WIRE when drawing schematics all these years, never had any problem making PCBs from it... and I have thousands of boards/products out there in the field.

This is the icon I click in Eagle.

Okay, using the NET command saves me the step of placing a net junction as a separate task.
Other than that difference, if you look at properties, it's the same as using LINE then placing the junctions manually.
245  Using Arduino / Project Guidance / Re: +/- 22VDC Power Supply??? on: January 07, 2013, 11:54:22 pm
it will be traveling and shipped OFTEN.
Have you considered an internal, adjustable, regulated power supply -- powered by mains.
246  Using Arduino / General Electronics / Re: Newbie question on designing your own 'board' instead of using wires on: January 07, 2013, 05:52:01 pm
You don't need junctions at the IC pins, or component, or input/output terminals. They're understood as already being connected.

But when you have 2 net wires crossing, and they're supposed to be connected, yes, put a junction there.

247  Using Arduino / General Electronics / Re: Newbie question on designing your own 'board' instead of using wires on: January 07, 2013, 05:18:44 pm
You need to put junctions in your wire/schematic. I don't see any dots anywhere.

I dumped expresssch because I got the impression that I would get stuck
Good for you. Yeah, you want something that can output gerber so you can send the job to whomever you wish, and you're not tied up/hostaged by Express PCB.
248  Using Arduino / General Electronics / Re: Newbie question on designing your own 'board' instead of using wires on: January 07, 2013, 12:07:48 pm
I've been playing with DipTrace on and off... so far, I'm liking it's features. Haven't gotten to defining my own part yet.
It seems very powerful and lots of editing options...

It's fugly though on an OSX, and hate seeing the C:\Program Files\blah blah blah directory structure.
249  Community / Gigs and Collaborations / Re: Hard amplifier problem - Pleease anwer on: January 07, 2013, 11:55:42 am
This is an opamp. It's by definition a voltage amplifier.
Voltage Delta Gain = Vout / Vin  

You don't compute Iout/In in an opamp.

http://Cair to explain the difference then?
Most opamps have limited output current drive. You can use their outputs to drive another opamp, or a simple high impedance circuit.

But their outputs aren't beefy/strong enough to drive for example a 600 ohm load output transformer... and then several feet of cable behind that transformer's secondary.  They're going to get hot and just break down.

There are special opamps that have more current output drive that can drive these transformer loads. Or you can tack on a discrete transistor booster circuits at the end of the opamp to increase its drive capability.

So now you have a high current output driver, but still operating at unity (Voltage Gain = 1) (depending on resistor values/ratio).

You don't call this beefier opamp as having "current gain"... That's implying there is a proportional relationship between it's output current and the input current you feed into it.  

If you look at the datasheet for opamps having high output current capability, you'll find in the datasheet it's IOut (Output Current), example +/-26mA, and the load at which it's tested RL=600ohm, Vs=+/-17V.  

If you look at a simple/typical opamp datasheet, you won't find this spec listed.

Here's a 250mA high-speed, high output current buffer opamp. BUF634
Unity Gain, voltage gain=1. They don't call these opamps "current amplifiers" (or having current gain) just because it has a higher output current drive capability.
The BUF634 is a high speed unity-gain open-loop
buffer recommended for a wide range of applications.
It can be used inside the feedback loop of op amps to
increase output current, eliminate thermal feedback
and improve capacitive load drive.
For low power applications, the BUF634 operates
on 1.5mA quiescent current with 250mA output,
2000V/µs slew rate and 30MHz bandwidth. Bandwidth can be adjusted from 30MHz to 180MHz by
connecting a resistor between V– and the BW Pin.
250  Using Arduino / General Electronics / Re: Using an Unknown LED on: January 06, 2013, 08:42:05 pm
Compute your resistor for 10mA forward current and go from there... adjust if it's too bright or too dim.
251  Using Arduino / General Electronics / Re: Trying to assemble custom cables and housings? on: January 06, 2013, 08:04:27 pm
Thin solid wire taken from ethernet cables (I think 24-26AWG) bends very easily and snaps.
No no no no. You need braided wires.

What tool are you using to crimp?
252  Using Arduino / General Electronics / Re: Zener Diode not Zenering at all ;-( ... on: January 06, 2013, 02:39:09 pm
But if I rump up the power supply to 10 or 11V I can push Zener to about 4.8V. So, no protection there.

Look at the datasheet again.... and don't overlook the definition of minimum, nominal, and maximum. 
And don't forget how temperature may affect that too. look at the graphs.

You want something that regulates, put a proper 3-terminal voltage regulator there, and adjust it to whatever value you want.

I mean, all the tutorials on the web are talking about Zener diodes regulating voltage.
It's more of a voltage clamping device, not a "proper" voltage regulator.
253  Community / Gigs and Collaborations / Re: Hard amplifier problem - Pleease anwer on: January 06, 2013, 02:26:47 pm
there is a current gain even if there is no voltage gain.

An opamp by definition is a voltage amplifying device, not a current amplifying device.

Don't confuse more output current drive capability with current gain.

In fact, current output capability of any opamp can be further increased by strapping on discrete NPN/PNP booster circuit at it's output... but it's still a voltage amplifier.
254  Using Arduino / Installation & Troubleshooting / Re: fried my uno (whoops) fix.? on: January 05, 2013, 10:53:52 pm
Maybe kitty's house is mis-wired at one of the outlets? That's the only explanation for your breaker popping.

I'd call an electrician.
255  Using Arduino / General Electronics / Re: what's the difference??? on: January 05, 2013, 08:54:38 pm
The extended temperature version is a few dollars more expensive. If your project won't be experiencing below 0C temperatures, no need to get the more expensive stuff.

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