ARUni, AR Universal board - Page 2 - RC Groups
Thread Tools
Jan 06, 2016, 09:52 PM
Registered User
flygear's Avatar
Quote:
Originally Posted by flybabo
Don't put unnecessary 0.1uF caps to the switch inputs. It caused enough problem for many people. http://openrcforums.com/forum/viewto...42c8bd#p105985
I'm taking your "Ground bounce" suggestion very seriously and I'll remove all 0.1uF on AR9x Rev B for a test.

All kinds of switching testing and glitches will be generated to inputs, lets see if any side effects.

Removing all these anti-glitch caps save lots of room on the board too. not to mention save SMT process time as well.
Sign up now
to remove ads between posts
Jan 07, 2016, 02:50 AM
Over 65 years of R/C flying
Quote:
Originally Posted by flygear
I'm taking your "Ground bounce" suggestion very seriously and I'll remove all 0.1uF on AR9x Rev B for a test.

All kinds of switching testing and glitches will be generated to inputs, lets see if any side effects.

Removing all these anti-glitch caps save lots of room on the board too. not to mention save SMT process time as well.
I like small add-on boards optional. Please leave place to put .1 caps if you remove them. You can't test for all problems that might come up and they are put on because of long experience even though they might cause "ground bounce" they may be necessary in some cases. (Resistors in series may be a possible substitute.) Not all Transmitters and RF circuits are perfectly designed, they are often a compromise. Thanks for all your work.
Jan 07, 2016, 03:01 AM
Registered User
For the sake of completeness, why don't you add CS signal as well since there's a room for two more holes.
Actually, both WR and CS can be permanently tied down.

As for the daughter board, just provide 4 solder pads for USB wiring in case taking out the USB connector which is slightly thicker than MicroSD adapter.
I'm planning to remove the USB connector in AR9x daughter board for my single stick project and it requires thin wire soldering.
Jan 07, 2016, 09:05 AM
Registered User
flygear's Avatar
Right, better have CS as well.
RW is already there.
On the FFC ribbon conntor, CS & RW are already tied down, so those two pins can be sued for someother uses. they are already in Ersky9x option.
In some case, anybody wants to use CS&RW to LCD connection, those signal can be linked with adding 0 resistor or tiny jumper wire.

you can remove micro sdcard socket out, but I prefer to keep it there for the easy use of usb between PC and TX.
Last edited by flygear; Jan 07, 2016 at 09:10 AM.
Jan 07, 2016, 09:08 AM
Registered User
flygear's Avatar
Quote:
Originally Posted by tedbmoss
I like small add-on boards optional. Please leave place to put .1 caps if you remove them. You can't test for all problems that might come up and they are put on because of long experience even though they might cause "ground bounce" they may be necessary in some cases. (Resistors in series may be a possible substitute.) Not all Transmitters and RF circuits are perfectly designed, they are often a compromise. Thanks for all your work.
Don't fix unless it's broken. I agree.

I think AR9x has proven with 0.1uF caps with 100Rs.
However, I still like to test without 0.1uF caps.
Thanks.
Jan 07, 2016, 05:06 PM
Registered User
It boils down to amount of stray inductance it developed.
If there's very small stray inductance, you won't see any problem.
Also, small amount of overshoot/undershoot are effectively clamped down by on chip zener diodes.

However, you should ask yourself why you put 100ohm and 0.1uf cap.
As I stated:
(i) switch glitch/bounce is handled by software and putting a cap won't eliminate the glitch - you need a latch to eliminate the glitch,
(ii) no need to put a cap to protect switch contact since switching current is less than 0.5mA (if you really want to do it, you should solder a cap to the switch pins),
(iii) if RF signal is powerful enough to upset 3.3V logic level, that radio couldn't get FCC approval and it will affect many other devices like pacemaker.
Undershoot / overshoot voltage caused by LC is far higher than RF induced noise level.

I don't think even 100ohm resistors are necessary since all the pins are configured as input when powered up and
even if an output pin gets shorted, it will not burn immediately since output current is limited.

I looked into old Kraft / Proline schematics and inspected several old Futaba radios. There're no such caps and resistors on the switches.
MStar2K encoder used by many vintage radio conversion projects has no such cap and resistor on the switch yet no one has ever reported a single problem related to the switch.

Most modern integrated circuits are designed to meet minimal or no external component requirements
mainly because customers keep asking it to reduce the cost of their end products.
If it needs any external components, it should be documented in the datasheet.
Please take a look into the SAM datasheet/application notes whether they recommend such cap/resistor.

From a chip designer's point of view, I've seen many board designers putting unnecessary caps and resistors simply because they believe that it might be useful to protect the chip.
There're lot more protection circuits in the IO buffers of the chips than you thought.

Sometimes, believing is deceiving
Last edited by flybabo; Jan 09, 2016 at 03:41 PM. Reason: Fixed a typo
Jan 07, 2016, 08:57 PM
Registered User
Quote:
Originally Posted by flybabo
(i) switch glitch/bounce is handled by software and putting a cap won't eliminate the glitch - you need a latch to eliminate the glitch,
I agree with flybabo.
Tau is 10uS with 100ohms and 0.1uF. Chatter is a mS order. It won't work.
BTW, a rotary switch (for F Modes) has not only chatter, but is usually break-before-make unless it is specified otherwise. FW is easily fooled if it does not have several loops for detecting the stable state. The F/W solution applies to any other mechanical switches as well.

Quote:
Originally Posted by flybabo
(ii) no need to put a cap to protect switch contact since switching current is less than 0.5mA (if you really want to do it, you should solder a cap to the switch pins),
I agree, again.
Almost all mechanical switches can easily handle a few mA even with rubber contact key switches.
Actually, old school practice is to put some sub-mA thru any mechanical contacts to break oxidation film. Nowadays, many switches are smaller, gold plated, and somewhat hermetic sealed, so it may not be a big issue, I guess. But it is still a good practice for open-contact/mechanical switches such as toggle and rotary switches. Of course, without any caps across, please.

Quote:
Originally Posted by flybabo
(iii) if RF signal is powerful enough to upset 3.3V logic level, that radio couldn't get FCC approval and it will affect many other devices like pacemaker.
Undershoot / overshoot voltage caused by LC is far higher than RF induced noise level.
I agree.
In the logic circuit, "AC" impedance of the signal line is very low and nearly grounded thru the saturated quadrant of the transistor. I did have a problem with WiFi TX imbedded in a 2.5GHz Cellular Device, but that was not by RF interference to the logic, but to the front end of the 2.5GHz RX.
Jan 07, 2016, 10:11 PM
Registered User
flygear's Avatar
what I most beleive is the test results, I'll read through datasheets and will do tests on R and Caps on most signal inputs.

Another topic I like to hear about is the DC charging circuit for those use NiCd/NiMh as Tx battery.
How serisouly we want this?
Jan 07, 2016, 10:46 PM
Registered User
I am not sure what's the issue on the charger... I have a large variety of transmitters, and I use either JR or Futabba charger depends on the charge plug polarity. Wall chargers have high output impedance at 10~12V average with higher ripple voltage making enough for trickle charging over night.. or usually a week
May be I am missing something...
Jan 07, 2016, 11:04 PM
Registered User
Since my preferred battery choice is two Panasonic 18650 Li-Ion batteries, people like me may feel onboard NiMH charger as an overhead
Instead of putting a charger, it would be nice if you put a switching regulator rather than a linear regulator.
A buck converter type switching regulator is cheap and very efficient - it makes the board more power efficient.
Jan 07, 2016, 11:07 PM
Registered User
flygear's Avatar
Original AR9x doesn't have DC jack in charger feature due to many reasons

However, this board is different , so should we put one?
or should we leave it out?
Jan 07, 2016, 11:09 PM
Registered User
flygear's Avatar
flybabo,

Switching regulator, that's one good thing to consider.
Let me double check on their price before get you firm answer.
Thanks.
Jan 07, 2016, 11:33 PM
Registered User
Quote:
Originally Posted by flybabo
Since my preferred battery choice is two Panasonic 18650 Li-Ion batteries, people like me may feel onboard NiMH charger as an overhead
Instead of putting a charger, it would be nice if you put a switching regulator rather than a linear regulator.
A buck converter type switching regulator is cheap and very efficient - it makes the board more power efficient.
Oh....18650 Li-Ion. They are GOOD!
Before Li-Po days, we bought a bunch of used Nokia phones and scavenged them for GWS foamies. Yes, it needed 3..80V? with a constant current power source. We didn't care about the balance circuit then, but you folks plan to add one more wire(s) for it?
Jan 07, 2016, 11:55 PM
Registered User
Quote:
Originally Posted by signalone
Oh....18650 Li-Ion. They are GOOD!
Before Li-Po days, we bought a bunch of used Nokia phones and scavenged them for GWS foamies. Yes, it needed 3..80V? with a constant current power source. We didn't care about the balance circuit then, but you folks plan to add one more wire(s) for it?
Panasonic produced the highest capacity 18650 (NCR18650B: 3400mAH, 3.7V) and equivalent cells are powering Tesla Model S.
I'm also using 3.6V 2400mAH (CGR18650) cells.
Both are good and delivered claimed mAHs.
Note that most no name 18650 cells sold in eBay have fake mAHs.
I'm feeding a balance line to 6pin DIN connector found on old Kraft/Proline and charging two cells with an external balanced charger.
Jan 08, 2016, 12:08 AM
Registered User
Quote:
Originally Posted by flygear
flybabo,

Switching regulator, that's one good thing to consider.
Let me double check on their price before get you firm answer.
Thanks.
I bought those and use it everywhere
http://www.ebay.com/itm/10pcs-Mini-3...kAAOSwyQtVg3xC
All you need is a buck converter chip, a 100uH inductor and several passive components.
Every FrSky RF modules have one of such.
Or more expensive end product like this:
http://www.mouser.com/ProductDetail/...ChwaAliu8P8HAQ