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Author Topic: Please evaluate my schematic for glaring errors  (Read 465 times)
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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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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.
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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.)

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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.
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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. 
« Last Edit: December 25, 2012, 08:46:25 pm by jerseyguy1996 » Logged

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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.
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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?
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Thanks!  Is that how you make the little square arrow with the name of the connection that it goes to inside of it?
Eagle might have such a part, but it isn't necessary.

If you use the NAME command, you can name a net (or wire).  Then you can use the LABEL command to add the net/wire's name to the schematic.
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