Author Topic: My first board design. Feedback appreciated!  (Read 2936 times)

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Offline aeharding

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My first board design. Feedback appreciated!
« on: September 28, 2015, 11:32:16 pm »
(I posted this on Reddit, but I was hoping you guys would offer some help! Thanks)

Hey everyone, this is my 'first' real PCB design. I'm a web developer by trade, and I've been fascinated by PCB design for the last week after painstakingly making a perfboard prototype. It's an audible altimeter for skydiving. I put it in my helmet and it beeps to let me know when I should deploy my parachute at what altitude. I've gone through a couple iterations (breadboard, perfboard) with real world testing, and now I'm hoping to make an actual PCB to lower the footprint and add a rechargeable battery.

I have a few questions:
1) Are the decoupling caps used correctly?
2) Would you recommend breaking out tx/rx / FTDI? Or is this enough?
3) I'm planning on using the pushbutton to allow the micro to be switched on and off with an interrupt and sleep mode. Should I do any debouncing? I think I can do it all in software, but I'm not entirely sure.

Any other design oriented suggestions are welcome. I am planning to add a better silkscreen in the future after it is finalized. This is only my first real PCB design. I can definitely redo it. (I've already redone it twice!)

Also, I'm looking to conserve power. Let me know of any ideas. I tried using an ATTiny, and I had issues with I2C... So Atmega328 is what I chose. :) I'm planning on using the micro to control the 3.3v reg, as you can see in the schema.

Please let me know of any concerns... Thanks! :) I can post eagle files if needed.

http://imgur.com/a/V9xAa
 

Offline alexanderbrevig

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Re: My first board design. Feedback appreciated!
« Reply #1 on: September 28, 2015, 11:40:06 pm »
Welcome!
After a rough glance it seems to me you'll need a bettery actually connected (and regulator enabled in order for you to use the barometric sensor. Is this intended?

Also, I would not cut out decoupling capactiros for the AVCC and VCC lines. Be sure to place capacitors close to the pins for best performance :)
 

Offline aeharding

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Re: My first board design. Feedback appreciated!
« Reply #2 on: September 29, 2015, 02:15:25 am »
Welcome!
After a rough glance it seems to me you'll need a bettery actually connected (and regulator enabled in order for you to use the barometric sensor. Is this intended?

Also, I would not cut out decoupling capactiros for the AVCC and VCC lines. Be sure to place capacitors close to the pins for best performance :)

Thanks Alexander

I have a battery connector on SL1 for a lipo 1s battery. The micro runs within the battery's discharge curve, but the barometric sensor/buzzer do not, so they are connected to the regulator. That is intended (along with the micro having the ability to switch the reg on and off) in order to save power in standby. Let me know if that makes sense :)

What are you mean by not cutting out the decoupling capacitors?

Thanks!
Alex
 

Offline jwm_

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Re: My first board design. Feedback appreciated!
« Reply #3 on: September 29, 2015, 02:46:36 am »
Have you checked the quiesent current of your buck-boost regulator/minimum load? Some can be quite voracious. I recently ran into one with a 20ma standby current independent of load. And to think I originally added it in to improve battery life, trading losing half a ma via a linear regulator for 20ma continuous draw. doh.

Offline aeharding

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Re: My first board design. Feedback appreciated!
« Reply #4 on: September 29, 2015, 02:58:28 am »
Have you checked the quiesent current of your buck-boost regulator/minimum load? Some can be quite voracious. I recently ran into one with a 20ma standby current independent of load. And to think I originally added it in to improve battery life, trading losing half a ma via a linear regulator for 20ma continuous draw. doh.

Hey jwm,

I hope the real world performance will be on par to the specs -- this specific buck-boost has 16uA quin current, with < 1 uA while disabled. :)

http://www.linear.com/product/LTC3531

With the micro on standby of < 1uA, I'm hoping to get a month or more of battery life.
 

Offline ralphd

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Re: My first board design. Feedback appreciated!
« Reply #5 on: September 29, 2015, 03:17:20 am »
I'd go with a 662k ldo to reduce board space and save cost.  If the barometic sensor can take 4.2V then drop the regulator.  Or run directly from a LiFePO4 battery.
Try driving the piezo directly; you may get enough volume and then can drop the transistor.
If your code size is not large you could save a bit by using an ATmega8a.
Is the 10-pin header ICSP? The 6-pin version would save some more board space.
Lastly, if the barometric sensor needs less than 5mA, you could run everything off a CR2032.
Unthinking respect for authority is the greatest enemy of truth. Einstein
 

Offline microbug

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Re: My first board design. Feedback appreciated!
« Reply #6 on: September 29, 2015, 07:04:19 am »
Step 0: use KiCad (or anything else but Eagle).
It's not your beliefs that make you a better person, it's your behaviour. — Greywoolfe  •  microbug.uk (not yet complete)

Just because I have lots of posts, doesn't mean I'm any good at this!
 

Offline obiwanjacobi

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Re: My first board design. Feedback appreciated!
« Reply #7 on: September 29, 2015, 02:22:14 pm »
Quick scan:

Only one terminal of SL1 is connected? Also the pad right next to it is unconnected.
There are a number of holes that seem to serve no purpose?

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Arduino Template Library | Zalt Z80 Computer
Wrong code should not compile!
 


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