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151  Using Arduino / Project Guidance / Re: Solder footprint question on: December 28, 2012, 10:31:50 pm
Nothing. It's just drafting style.

The (5) smaller lands are for the connections. The (6) larger lands are just for supports. Look at the mechanical drawings. 

(when you're pushing and pulling plugs, you don't want those (5) small lands to be the only thing holding your part on your PCB. They won't be able to take the stress. The bigger lands hold the part, i.e. welded to the PCB.)

Thanks!  That is what I thought but I wanted to be sure.
152  Using Arduino / Project Guidance / Re: Solder footprint question on: December 28, 2012, 10:31:24 pm
are you making a stencil so a machine can screen paste it?

No....just creating a new part for my Eagle library to use on my board.
153  Using Arduino / Project Guidance / Solder footprint question on: December 28, 2012, 09:37:51 pm
On this data sheet:

http://www.molex.com/pdm_docs/sd/473460001_sd.pdf

they show the recommended solder footprint for this part.  Is there any significance to the fact that the hashmarks on the 5 pin pads are going a different direction than the hashmarks on the 6 larger pads?
154  Using Arduino / Project Guidance / Re: Modifying the solder stop mask for a pad in eagle on: December 27, 2012, 09:17:59 pm
If you're asking to make the stop mask larger, then you would select the polygon tool, select the tStop layer, then draw the polygon so it overlaps the existing stop mask; the two will combine to create a larger area as you would expect. If you're trying to make a stop mask smaller then you would need to modify the IC package and remove the pad completely, then manually create the stop mask and pad using the polygon tool.

When your project is complete it's always a good idea to doublecheck the results using a Gerber viewer (like GerbV, etc.).

My goal is to make the stop mask smaller.  I read somewhere that the router will only work if you use the pre-made pads in eagle.  Is this incorrect?  I do have something worked out but I am not sure if it is the appropriate way to solve the problem.  The first picture below is the original part with .5mm pitch SMD's.  As you can see, the stop mask almost touches.  The second picture is one where I turned off the stop mask on the pad and then placed a new polygon on top of it with the correct dimensions and assigned it to the tStop layer.  Will this work?


big_tStop by jg1996business, on Flickr


small_tStop by jg1996business, on Flickr

155  Using Arduino / Project Guidance / Modifying the solder stop mask for a pad in eagle on: December 27, 2012, 06:35:09 pm
Is the only way to do this to turn off the stop mask for a specific pad and then draw a new rectangle of the appropriate size and set it to the tStop layer?
156  Using Arduino / Project Guidance / Re: Arduino Solar MPPT battery charger on: December 27, 2012, 05:41:11 pm
Atmel has a great app note for a battery charger reference design that they sell.  I considered using an AVR uC before finally settling on the BQ2031.  If you read through the whole thing cover to cover you will learn a ton about what you are trying to put together.

http://www.atmel.com/images/doc1659.pdf

157  Using Arduino / Project Guidance / Re: LED current limiting resistor on: December 27, 2012, 05:25:13 pm
Here is what the people making those devices are trying to tell you.

1) the If vs. Vfwd curve comes the led datasheet.
2) The thick green curve comes from those nice folks at Atmel. They are the I-V curve of a mcu's pin.

The two curves together determines the output current on the led, without any resistors. It is about 15ma If and 3v Vfwd. That's due to the pin's internal resistance (0.3v / 15ma = ??? ohm).

If the pin had no output resistance, its I-V curve would be like that red line at 3.3v. The output current would then be at 30ma.

That is essentially the basis why some designs have no serial resistors.



Great information!  I will have to work my through what you did there so that I will be able to understand it better.  Kinda wishing I had done engineering in school now.
158  Using Arduino / Project Guidance / Re: LED current limiting resistor on: December 27, 2012, 05:22:04 pm
I am pretty sure you are going to have a problem using a simple 3.3V regulator with a 3.7 lipo.

Dropout voltage on a typical 3.3V regulator is going to be a little bit over 4V. So if you fully charge a Lipo and pump it through a standard 3.3V regulator you are going to have a very short life cycle if at all. I don't remember the exact number but at 4.2V, your regulator might be supplying less than 3.3V right out of the gate and it will fall off rapidly from there.

Even a Low Dropout Voltage Regulator is going to struggle in this case since your operating voltage is so close to the maximum voltage of the battery.

What you need is a Boost Convertor that will regulate your 3.3V down to less than 1V.

Here is one from Sparkfun that would work perfectly for what you are trying to do:

https://www.sparkfun.com/products/10255

This one is even better since it has a a charge circuit built in as well and is only about $5 more.

https://www.sparkfun.com/products/11231

If you already know all of this then I apologize.




I'm actually using one of these (although time will tell if I will be able to successfully solder it).

http://www.mouser.com/Search/ProductDetail.aspx?R=TPS62237DRYTvirtualkey59500000virtualkey595-TPS62237DRYT
159  Using Arduino / Project Guidance / Re: Fuel Gauge for Lipo? on: December 26, 2012, 02:52:13 pm
Sparkfun sells a few.  Here's one:

https://www.sparkfun.com/products/10617
160  Using Arduino / Project Guidance / Re: Switching mains--best way to power Arduino? on: December 26, 2012, 12:19:02 pm
I puchased a couple of these a few weeks ago but I haven't had a chance to try them out yet.  $3 each ain't bad and they handle a fairly broad voltage range.  Perhaps if anyone else has used something like this they could chime in.

http://www.ebay.com/itm/5pcs-New-5V-1A-built-in-industrial-power-switching-power-supply-board-module-/261055148156?pt=LH_DefaultDomain_0&hash=item3cc819707c
161  Using Arduino / Project Guidance / Re: Arduino Solar MPPT battery charger on: December 26, 2012, 12:00:37 pm
I made a charger using a TI BQ2031 IC and it regulates current at Imax until Vmax is reached, then regulates Vmax until current falls to a set percentage of Imax so for a 12 volt 4Ah battery I regulate current at 1C until voltage reaches 14.7 volts, and then maintain 14.7 volts until current falls to .25 amps.  Then I switch to a float charge of 13.5 volts to keep the batteries topped off.  When it is regulating the voltage at 14.7 volts, current will slowly fall as the battery charges.  For MPPT they have this app note:  http://www.ti.com.cn/cn/lit/an/slva378/slva378.pdf
162  Using Arduino / Project Guidance / Re: Please evaluate my schematic for glaring errors on: December 26, 2012, 10:00:51 am
Just a general suggestion: use net names so you don't have to physically drag wires to connect D3 to wakeup. Instead, you add a wire to the pin D3 and name that wire net "D3". Add a wire to wakeup and name it "D3". It's much more readable than tracing green wires with my eyes.

Thanks!  Is that how you make the little square arrow with the name of the connection that it goes to inside of it?
163  Using Arduino / Project Guidance / Re: Please evaluate my schematic for glaring errors on: December 25, 2012, 08:37:34 pm
No 22pf (x2) and 1M resistor around the crystal?  (or are you using a resonator instead?)

Is R4/R5 value too low? (don't know what kind of LED you're using)

Does it need to be a switching regulator? What's the power source? Can't you just use an LDO (Low Drop Out) linear regulator?

No bypass 0.1uf caps for U1, GPS module, U2, etc (Vcc pins)... You need those (just to be safe/proper.)
I'd probably add one in parallel with C1 too.

Might as well add a pull  up resistor from Mega-pin10 to Vcc (in conjunction with SW1).

Junction in your schematic missing (from P$2 of resonator to GND line). (When you design your board, the pcb layout module wouldn't know something is amiss.)



This is great!  I will make these additions and corrections!  Oh and yes, I am using this resonator:

http://www.mouser.com/Search/ProductDetail.aspx?R=CSTCE8M00G52A-R0virtualkey64800000virtualkey81-CSTCE8M00G52A-R0

I'm powering it from a 3.7V LiPo battery and I would like to get by with as small a battery as possible.  That is why I went with a switching regulator for the efficiency.  Not sure how much it will really help.  This will be something that my wife will carry with her when jogging so I want it to be as small and light as possible. 
164  Using Arduino / Project Guidance / Re: Please evaluate my schematic for glaring errors on: December 25, 2012, 08:32:25 pm
The TPS6xxxx series is a switching regulator.  Have you followed the datasheets directions on selecting proper components and PCB layout?  They are (relatively) tricky to get right.

The bottom of page 1 on this datasheet has the recommended PCB layout:

http://www.ti.com/lit/ds/slvs941e/slvs941e.pdf

and this is my layout in Eagle:


Vreg by jg1996business, on Flickr

I used the components that they recommend in the datasheet or if not available from Mouser, I tried to match up as many of the specs as I could.  I'm not really sure which specs were important to match up though.
165  Using Arduino / Project Guidance / Please evaluate my schematic for glaring errors on: December 25, 2012, 08:01:06 pm
Good Evening,

I finally feel like I have everything hooked up on my first ever eagle schematic.  I humbly ask anyone with even an ounce of knowledge on such things (which is an ounce more than I have) to please take a look at this tortured and twisted attempt at a gps logger and let me know if you see any major/glaring errors.  Certainly I am not asking you to go through and read the datasheets on the various devices.  Mostly I just want to know if I am missing a resistor/capacitor/diode/etc. anywhere.  Thanks in advance for any assistance you can provide.


GPS_LOGGER by jg1996business, on Flickr
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