[Moved]: Bluetooth Module and Crystal Placement on PCB and Error Issues

[tiwari.sachin]

Hello,

I am trying to communicate with RN4677 (Bluetooth Module from Microchip) from a Andriod device. We are having a issue with Bluetooth where

1. There is a delay in data reception (This happens randomly).

2. There probably is some data loss too (because of which I am getting some junk)

3. The signal strength is not that good (Works fine when the mobile is very close (less than half a meter) but have issues 1 and 2 when far.


I had two versions of PCB

1. First version was working relatively well.

2. Second version, I made some changes (did not touch Bluetooth section at all) but had the PCB done from another vendor. This version has more issues than the 1st. First was way too better.

I was using it for a thermal printer and noticed that the printer was sitting exactly above Bluetooth module (which has a metal casing) and this could be the problem.

So I decided to go with the new board design altogether. Here are the details




Above image is the TOP view of the PCB, the mechanism sits on the TOP side of the PCB (at rear) as shown

Also shown is the Grounding for Bluetooth.

The motor tends to heat up while continuous prints are given.



The image above shows the bottom view of the PCB where the Bluetooth sits and details of all the possible metal surrounding it.

There is no option to move the USB or screws as it has to fit the casing of the product.




The above image gives the details of the suggested grounding for bluetooth which I have followed.




The above image gives details of how the PCB is placed in the casing.

Note: There is a Li Ion Battery that will sit below the bluetooth as I donot have space to place the bluetooth on TOP layer. Had to do it at bottom due to space constraint.


Are there any changes needed or am I doing it correctly.

Any suggestions on layout design shall be very helpful as we are having a few issues with connectivity and data transfer on previous boards.




In the above image, you can see that I have placed the MCU and crystal (12Mhz) below the motor. As motor would heat up when there are continuous prints, this could probably effect the performance of the crystal.

Since there is no other space on PCB where I could use this, I somehow had to choose this as my final option.

I am not sure of the motor temperature when continuous prints are given but it does heat up a lot.

Am I placing the crystal in the right place and is the grounding around crystal correct?

 

[BradtheRad]

Your setup might be like my weather forecast gizmo that comes in two pieces: gateway, and desktop display. The gateway accesses the internet. It broadcasts to and from the desktop display, via custom radio frequency networking (I think).

The instructions say that they should not be located too close to each other. A few feet separation is recommended.

The reason has to do with close-quarter distortion, reflections, signal overload, etc. So perhaps this is causing problems in your setup?

 

[tiwari.sachin]

@BradtheRad... Since it is a bluetooth based handheld thermal printer, there surely is no option to have MCU and Bluetooth far away.

I tried all possible ways (I could think of) to check why there are data errors and signal loss but was not able to do so.

I tested at night and it was having a issue, the same thing when tested in morning gave a little better results. Did try this for a couple of days and the similar results.

How can I make sure that the new PCB will be right. I am under tremendous pressure to finish this properly this time

 

[BradtheRad]

If we play our radio while we are next to a radio transmitting antenna, our own radio is liable to overload, distort, etc. It is not designed to operate in the presence of intense radio waves.

Is it possible for you to reduce transmitting intensity? Or, install some kind of baffle/ absorber? Then your receiving unit might operate more reliably.

Can you use a utility which reports parameters such as:
* Bluetooth signal strength
* noise
* dropped frames
* successfully received frames
Etc.?

For computer wifi there is Netstumbler. There ought to be a similar utility for your device.

 

[tiwari.sachin]

Let me check on that.

Never heard of baffel absorber. Need to check on that too

 

[BradtheRad]

A baffle or absorber probably is not a part that you cana choose from a list, based on specifications.
It is a general term for a substance, or piece of material, or enclosure, etc., which might reduce the intensity of rf transmission.
It does not necessarily have a particular shape, or thickness, or texture, etc.
It might consist of one piece, or two or three.
It might be grounded, it might not be.
Etc.

What this means is that experimentation is required.

From your description, it sounds as though your devices are practically touching. This raises a question why you need wifi to communicate between them? Is it possible you'll have less trouble by making a direct cable hookup?

 

[tiwari.sachin]

BradtheRad...

Its not a Wifi, its infact the bluetooth.

I am designing a bluetooth thermal printer and at the same time the unit has to sit in a enclosure that is quite small and hence the space is limited.