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31  General Category / General Discussion / Re: Using 3D printer to make circuit boards. on: March 07, 2013, 11:00:47 am
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I've seen a few videos on the milling process and they didn't look fine enough to allow for SMD mounting.  Maybe I'm seeing the wrong videos?

Or someone is using the wrong machine.  Our guys make PCBs for SMT components on a Haas TM pretty regularly.  Takes all freakin' day because the mill only has a 4000 RPM spindle (it's designed for machining, not PCB milling) but other than that it works great for small stuff.  I know they've done 100 pin LQPF, I think some no-lead stuff, and smaller passives (0603 for sure, and I'm fairly certain 0402).

-j
32  Topics / Product Design / Re: PCB fabrication sites on: February 28, 2013, 06:53:37 am
OSHpark will do shapes.  You pay for the rectangle that your shape fits inside.
33  General Category / General Discussion / Re: Hakko Tip Thermometer on: February 28, 2013, 06:51:12 am
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The FG-100 read ...

300C

It was not even off by 1 deg at first, then went up to 302C after a bit.

So, which one is correct?
34  Community / Bar Sport / Re: Thursday - what to do? on: February 22, 2013, 09:35:31 am
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LEDs will fall silent

If your LEDs make noise, you may be doing it wrong...
35  Community / Bar Sport / Re: I'm A Student now! on: February 13, 2013, 03:57:45 pm
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Pretty difficult with just one MCU class one semester just my 2 cents. Only those motivated to do more will learn more.

Well, you've got to look at the whole program before getting the idea that it's only one semester.  Start with the freshman level intro to engineering where they'll do a project from a kit or an arduino project, add in a semester of programming and another of data structures, progress through the circuits and electronics labs where they play with resistors and power supplies and transistors, go through logic where they see gates and FPGAs, spend a semester in the embedded systems course, and finish off with a semester or two of senior design where they'll do something a bit more sophisticated, and they have a chance to come away with a reasonable education, especially given that they have to take literature and history and other non-technical stuff as well.

As for side projects for the motivated, we've got a student club building a satellite.  Delivery for payload integration on April 1, launch currently scheduled for mid-July.

-j
36  Community / Bar Sport / Re: I'm A Student now! on: February 13, 2013, 09:24:57 am
When you're in college, you're not there to learn about PIC or ATmega or any other specific product; you're there to learn how to use a microcontroller to solve a problem.  When you're in the real world, you'll do the math (e.g. like Osgeld says on cost of components vs. size of the run), look at the standard tools your company/group uses, or maybe just "use X because we've alway used X".  If you and your prof did your jobs, you'll know enough about solving problems with microcontrollers that you can adapt to the specific tools at hand.

-j
37  Community / Bar Sport / Re: How do you misuse sticky tape? on: February 11, 2013, 10:06:08 am
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12 volts 50 amps running though 22 gauge wire connected by twisting the ends and a little bit of electrical tape covering it

Isn't that called a fuse?

-j
38  Using Arduino / General Electronics / Re: Best wire for 0.1" crimp pins? on: January 30, 2013, 11:39:30 am
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Even none polarized pins like these have same exact issue

Yep, that web page says:
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They work with 22 to 28AWG wires, though 22AWG wires with thick insulation might be difficult to fit into the pins.

Which is probably from the datasheet, and more or less what I was getting at with the "thinner insulation".

There's not a "standard" other than the manufacturer's datasheet for that particular connector. I have some Molex connectors on hand that are for 0.1" headers with 0.025" square pins, and there are two different connectors - one for 22-24ga wire, and another for 24-30ga wire.  I think there's a third IDC variety as well.

Blah blah blah. The long, correct and sometimes painful answer is to read the datasheet, and any datasheets or specs that it references, and use what they say (including the $350 crimping tool designed for it).

The short answer is probably to find some 22ga with thinner insulation. smiley

Thanks for the link, BTW; I noticed Polulu had a crimp tool a bit nicer that the one I'm using for these, that's still within my budget.

-j
39  Using Arduino / General Electronics / Re: Best wire for 0.1" crimp pins? on: January 30, 2013, 08:03:22 am
Since I haven't seen these connectors and Sparkfun doesn't supply a datasheet, it's hard to tell for sure.  Sorta depends on what size your CAT5 wire is (most likely 24ga), and if it's stranded or solid. I would avoid solid conductor wire pretty much in any crimp connector, and any application where the wire will move.

It's possible you just need some different 22ga with thinner insulation.  If your CAT5 is smaller than 24ga, try 24ga wire.

-j
40  Using Arduino / Programming Questions / Re: SPI troubles with Bosch ASIC on: January 24, 2013, 03:32:33 pm
78H means 78 hex.  It's sometimes written as 78H.

In C we write it as 0x78, not 78H (and definitely not 0x78H).

Did 0x78H actually get past the compiler?  It shouldn't  My gcc (solaris and linux) dies with "error: invalid suffix "H" on integer constant" when I tried 0x78H.

-j
41  Using Arduino / Motors, Mechanics, and Power / Re: Motor current draw from 5V pin MADNESS! on: January 24, 2013, 09:53:41 am
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looks like your offcial USB specification is totally optional. Post your official USB specification link.

http://www.usb.org/developers/docs/usb_20_110512.zip

Download, extract, view file usb_20.pdf.  This document is:

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1.2 Objective of the Specification

This document defines an industry-standard USB.  The specification describes the bus attributes, the  protocol definition, types of transactions, bus management, and the programming interface required to design and build systems and peripherals that are compliant with this standard.

So, this is the official standard.

Section 7.2:

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This section describes the USB power distribution specification.

Section 7.2.1:

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The power source and sink requirements of different device classes can be simplified with the introduction of the
concept of a unit load.  A unit load is defined to be 100 mA.  The number of unit loads a device can draw is an
absolute maximum

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A device may be either low-power at one unit load or high-power, consuming up to five unit loads.  All devices default to low-power.  The transition to high-power is under software control.  It is the responsibility of software to ensure adequate power is available before allowing devices to consume high-power.

So, your device can have "1 load unit", or 100mA, for free.  If your device wants more than 1 load unit/100mA, it may be configured for up to 5 load units (500mA) after appropriate software-controlled negotiation.

I know my original arduinos did not have the FTDI chips configured to negotiate for the full 500mA (use the FTDI-supplied configuration tool to examine/change this).  I don't have any of the newer Atmel USB interfaced arduinos, so I don't know anything about their power negotiation characteristics.

-j
42  Using Arduino / Motors, Mechanics, and Power / Re: Motor current draw from 5V pin MADNESS! on: January 22, 2013, 02:47:10 pm
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Probably better stated as "it depends".

http://en.wikipedia.org/wiki/Universal_Serial_Bus

I guess wikipedia trumps the official USB specification.  smiley-neutral

-j
43  Using Arduino / Motors, Mechanics, and Power / Re: Motor current draw from 5V pin MADNESS! on: January 21, 2013, 09:54:13 pm
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That is probably a minimum specification so manufacturers of

No, 500mA is the maximum for USB according to the USB specification (versions 1 and 2, anyway, not sure about USB3).

USB spec says a device can have 100mA for "free", and can negotiate with the host for up to 500mA.  In practice, many hosts will supply 500mA without negotiation.  There are also other deviations from that spec, such as the Macs that provide 1A or more for charging iPads.

Powering a motor directly from an output on the arduino will kill the processor - maybe one output pin, maybe the whole IC.  The maximum for a single pin is 40mA (that's on the original ATmega8, newer may be a bit higher but similar).

Keep trying to drive a motor from an output pin and you will kill your arduino, if you haven't already.

-j
44  Using Arduino / Motors, Mechanics, and Power / Re: using ESC to control motor speed on: January 17, 2013, 04:55:57 pm
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what do you mean current capacity?
Voltage is only one component of the electrical power provided by a battery.  The other is current.

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how do i know what a batteries current capacity is?
The only sure way is to read the datasheet.

Some chemistries provide more current than others. In general, larger batteries of the same chemistry provide more power than smaller batteries.

If your 9V battery is like this, it's a very small size of a lower powered chemistry, so you're only going to get a few tens of milliamps of current.

-j
45  Using Arduino / Motors, Mechanics, and Power / Re: using ESC to control motor speed on: January 16, 2013, 05:28:44 pm
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the ESC is connected to a regular 9V battery for power supply

Ah, you don't mean the little rectangular 9V "transistor" battery, do you?

There's not nearly enough current capacity there to run a motor as large as that one looks.

-j
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