¿ªÔÆÌåÓý

  1. BITX20
  2. Messages
Single Messages Topics Expanded Polls

Re: Different display issues

Jack Purdum
 

Hi Darryl:

The Mega2560 Pro Mini seems to be running fine and, like I said, we made this PCB for an antenna analyzer and it seems to be working great using both the AD9850 and the Pro Mini. As I've admitted many times before, I'm a software guy and the finer points of the electronics is just a little short of voodoo to me...but I'm trying. Farrukh Zia (K2ZIA) is a professor in the EE department at The City College of NY and designed the board, but I'm using it for a purpose outside of his design. Obviously, I using it inappropriately...my bad!

That said, I will give these suggestions a try. I already have added some caps to the power rails, but perhaps it still needs more. I still have the flicker and noise.

I'm passing your ideas onto Farrukh, as we are making a new PCB for this project as I think my club will be doing a build of this. The new board brings out more of the I/O lines so the Mega is more hackable than it is now. I have a few more things I want to hang on the rig and will need access to more pins that I have currently. Your ideas may influence his design.

I'll keep you posted. Again, thanks!

Jack, W8TEE


From: Darryl Harvey <darryl@...>
To: [email protected]
Sent: Tuesday, January 24, 2017 7:35 AM
Subject: Re: [BITX20] Different display issues

Jack,?

Just did a bit of checking and the specs for the Mega2560 Pro Mini says that it needs a 7-12V supply. ?Your circuit shows this as 6.6v.
This may be a little low of the onboard 5V regulator to function correctly?

Can you bump this supply up a bit ?

Also, your circuit doesn¡¯t show any decoupling caps before or after your power regulator.
you should have some 100nf Caps, and some ~10uF caps for some decoupling before and after the supply regulator.
Also with your circuit and the diodes to drop it down to 5v, again, no decoupling caps.?
and again down to 3.6v via diodes you have no decoupling..

Are you sure your AD9850 is 3.3v?? ?Mine is 5v.

Either way, again, you can power this from the 3.3v output from the Mega2560 Pro Mini 3.3v Output.

What I would do: ?Raise you supply voltage to 8V, supply the Mega2560 Pro Mini Vin this 8V. (provide decoupling caps before and after the regulator)
or if your supply voltage never goes above 12V, feed the 12 V into Vin on the Mega2560 Pro Mini. (again, decoupling caps never hurt)
From the 5V output of the Mega2560 Pro Mini, power the SWR Bridge, AD9850 and TFT display.
And if your DDS is 3.3v, power this from the 3.3v output of the Mega2560 Pro Mini.

If you do what I suggest above, you should be ok. (Assuming you have power problems - which it looks like)

Hope this makes sense.
let me know how you go.
Good luck
Darryl?
VK3DAZ


On 24 Jan 2017, at 11:26 am, Jack Purdum via Groups.Io <econjack@...> wrote:

Thanks Darryl...that gives me something to check into...it's appreciated!

Jack, W8TEE

From: Darryl Harvey <darryl@...>
To: [email protected]
Sent: Monday, January 23, 2017 3:36 PM
Subject: Re: [BITX20] Different display issues

Hi Jack,
I have been battling "noise clicks" for some time now in my DDS. I have tracked it to the i2c bus SDA data being injected in the power rail by my OLED display, the bitx is so sensitive it acts on this noise, my Mst3 with the exact same DDS doesn't have this problem.?

Anyway, the only way I could reduce this noise after many tests and redesigns was to put a D.C.-D.C. Isolator in the power rail for my OLED display. it didn't remove it 100%, more like around 95% - but at least it was usable.?
A simple voltage regulator (7805) and associated filter caps and even chokes didn't help.?

Even though the clicks occur when moving the encoder, it was the display updates causing the noise for me. ?When I moved to a TFT or LCD display I didn't have this issue, but check that your voltage supply to the DDS is not under load, that could cause some noise on updates.

Hope this helps
Darryl
VK3DAZ


On 24 Jan 2017, at 6:39 am, Jack Purdum via Groups.Io <econjack@...> wrote:

All:

I have my B40 with Raduino display and it works as advertised. I am now trying to add my TFT display and DDS VFO, which is a AD9850, more-or-less the same as the VFO in the Forty-9er article (March, 2016 QST). I am using a rotary encoder to change the frequency, again the same as before. The processor is a Mega 2560 Pro Mini; too many things going on for a Nano. I've used the TFT display, DDS, and Mega boards on an antenna analyzer project and had no issues. (Schematic attached, the SWR bridge is omitted.) However, on the B40, any movement of the encoder can be "heard" in the receiver audio. Also, there is a slight dimming, or flicker, of the display when rotating the encoder.?

As I've said many times before, I'm a software guy so the EE stuff leaves me not knowing where to begin. Any ideas sincerely appreciated.


Jack, W8TEE
<Figure33.jpg>
Join [email protected] to automatically receive all group messages.