Author Topic: another poorly-designed cheap Chinese AVR board  (Read 2348 times)

0 Members and 1 Guest are viewing this topic.

Offline ralphd

  • Frequent Contributor
  • **
  • Posts: 442
  • Country: ca
    • Nerd Ralph
another poorly-designed cheap Chinese AVR board
« on: September 29, 2015, 11:22:38 pm »
I recently bought a 268c UNO compatible board.  While some things are nice like the extra holes for breakout pins, whoever designed the board didn't know that SMD ceramic resonators shouldn't have external loading caps.  I've seen Chinese boards *without* parts populated that should be there, but this is the first time I've seen one with parts that shouldn't be there.
http://nerdralph.blogspot.ca/2015/09/under-3-chinese-arduino-uno-compatible.html

While removing the caps got the clock frequency within +- 0.5%, I think I'll also try changing the clock fuse settings to full swing instead of low power to see if it makes more of an improvement.
Unthinking respect for authority is the greatest enemy of truth. Einstein
 

Offline amyk

  • Super Contributor
  • ***
  • Posts: 6619
Re: another poorly-designed cheap Chinese AVR board
« Reply #1 on: September 30, 2015, 12:38:41 am »
They decided to go with cheaper resonators instead of crystals and forgot to remove the caps? Also, not all resonators have built-in loading caps.
« Last Edit: September 30, 2015, 12:44:17 am by amyk »
 

Offline ralphd

  • Frequent Contributor
  • **
  • Posts: 442
  • Country: ca
    • Nerd Ralph
Re: another poorly-designed cheap Chinese AVR board
« Reply #2 on: September 30, 2015, 01:45:10 am »
They decided to go with cheaper resonators instead of crystals and forgot to remove the caps? Also, not all resonators have built-in loading caps.
The resonators often aren't any cheaper than hc49 crystal oscillators.  The SMD resonator has 3 pads, like the ones with loading caps.  The timing improvement from removing the caps also indicates the resonator has internal caps.
Unthinking respect for authority is the greatest enemy of truth. Einstein
 

Online westfw

  • Super Contributor
  • ***
  • Posts: 3125
  • Country: us
Re: another poorly-designed cheap Chinese AVR board
« Reply #3 on: October 01, 2015, 09:56:05 am »
I find it ... philosophically interesting ... that these boards HAVE been designed (even if poorly.)  The stereotype and expectation for the cheap boards is that they'll all be copies of some (probably reasonable) design from somewhere else.   And yet, we see boards with no bypass caps, boards with extra crystal caps on a resonator, boards with no input/output caps on the regulator, a variety of usb/serial converter chips/circuits, a variety of extra connector footprints, and so on.   In a way, it's very encouraging...
 

Offline ralphd

  • Frequent Contributor
  • **
  • Posts: 442
  • Country: ca
    • Nerd Ralph
Re: another poorly-designed cheap Chinese AVR board
« Reply #4 on: October 01, 2015, 11:03:44 am »
I find it ... philosophically interesting ... that these boards HAVE been designed (even if poorly.)

Agreed.  I think it proves what a drama queen Banzi is with his attack of the clones hype.
Unthinking respect for authority is the greatest enemy of truth. Einstein
 

Offline richardman

  • Frequent Contributor
  • **
  • Posts: 427
  • Country: us
Re: another poorly-designed cheap Chinese AVR board
« Reply #5 on: October 05, 2015, 08:19:07 am »
I find it ... philosophically interesting ... that these boards HAVE been designed (even if poorly.)  The stereotype and expectation for the cheap boards is that they'll all be copies of some (probably reasonable) design from somewhere else.   And yet, we see boards with no bypass caps, boards with extra crystal caps on a resonator, boards with no input/output caps on the regulator, a variety of usb/serial converter chips/circuits, a variety of extra connector footprints, and so on.   In a way, it's very encouraging...

So you are saying that it's like the test for bridge loading: you build a robust bridge, and then start removing stones until it falls down. Then you rebuild with the last stone un-removed?  :-DD
// richard http://imagecraft.com/
JumpStart C++ for Cortex (compiler/IDE/debugger): the fastest easiest way to get productive on Cortex-M.
Smart.IO: phone App for embedded systems with no app or wireless coding
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf