Metal Box and Bluetooth and WIFI


#1

Hi all, as a completely new user I ask myself if the often described metal box for Zynthian will allow to use WIFI and/or Bluetooth on a Raspberry 3 without any additional antennas / equipment. What is the user experience for this ?


#2

Hi Tom @music.friend,

I have no experience with a Raspi in a metal box. But I know that a ESP8266 in a metal box does not work until you use one with an external antenna. So I think this will be the same for a Raspi - but no labority-tests by myself until now. I think Google may help…?

Regards, Holger


#3

I can confirm the @C0d3man theory. BT and WiFi are almost useless when the board (rPI in this case, but I tried with Particle Cores and Bluelight Beans) is in a metal box.


#4

Hello Holger,

thanks for the info. Indeed I have had difficulties with signal strength with RPi3 in a metal housing (Wifi). If you want to go wireless that leaves only to sacrifice USB for an external (Wifi and/or Bluetooth ??) add-on…

On the other hand I cannot see reasons for wireless transfers e.g. on stage because that could be hacked from some bad guys in the audience - I’ve seen that happen with wireless microphones. Leaves decision for RPi3 only for general performance improvements …
greetings, Tom


#5

Hi, Axeman,
thanks for confirming my suspicions!
Leaves preference for RPI3 over RPI2 mainly for imrpved performance…


#6

Hi @all!

I’ve tested the internal RBPi3’s Wifi in my zynthian steel case and it works. The signal “flows” out the case by the screen window or the little ventilation slots. Tomorrow i will try with the aluminum case and will try to compare the signal level with and without case in both cases.

Regards!


#7

You’re lucky :slight_smile:

A 2450MHz signal with a wavelenght of about 12cm can’t pass “through” a hole. Maybe the holes in the case have sizes so that holes act as a coupled antenna element and allows signal to enter the box.


#8

Screen window is 7cm long … perhaps it’s enough?


#9

Hi, thanks for your experiments!
How far away from your wifi router did you place the zynthian metal box ?
May well be that the “escaping signal” is strong enough for short distance, but in my case the touter is a bit away from the planned zynthian work place. Anyhow, good to know that it seems to work on short distance.
Would the same also apply to bluetooth ?
regards …


#10

Hi @music.friend!

My test was performed with the router really close to the Zynthian Box. Not more than 1-2 meters.
This morning i’ve tried with the router in the next room, not too far, but it didn’t worked. I want to repeat the test with a battery pack to measure the maximum distance i can reach. I think the signal that goes through the box is really low, so probably the distance wont be too big. Will see …

I’ve not tested the Bluetooth. Currently it’s disabled in the Gorgona image. There is some problems when enabling the bluetooth as it uses the the first serial port (AMA0), that is the port used for MIDI-IN. The second serial port is not well suited for that, so we have a problem here. Anywhere, i’ve to research a little bit more … it’s a tricky problem :wink:

Regards!


#11

A quarter wavelength is critical. At 2.4GHz a metal grid with 3cm squares has a massive damping to the signal, although you can see through it.
So the LCD-hole should be no problem…but the metal near the antenna will influence and detune the small integrated chip antenna. The impedance mismatch will lead to less radiated power and heat up of the integrated RF amplifier (the rf not radiated returns to the PA which has to dissipate the power. If too much you can blow your Wifi. But i asssume the Wifi chip regulates the RF power down in case of bad matching). It also can lead to internal elecromagnetic interference at the RPi.

But…it could work :wink:


#12

The new cases will have a square hole in the bottom, just under the SD card. This hole is mainly thought for inserting/removing the SD card, but as it’s very close to WIFI anthena, it will improve the signal with RBPi3 internal WIFI.

I made some tests and it worked quite well :wink:

Regards!


#13

hi guys,
thanks for bringing this update!
I myself had some problems with RPi3 in metal cases, especially e.g. when my router was sitting “upstairs”. So i did a little investment and bought an inexpensive external Wifi-USB adapter which solved the problem for some time.
Disadvantages:
… using up one USB port plus (although little) extra cost.

So thanks again for the working info and I’ll wait for that new metal box.
IN Addition: Is your update also valid for Bluetooth ? I’d like to use a spare Bluetooth keyboard for (Terminal) data entry, and that would not be as distant as my Wifi router.
regards, Tom


#14

The idea of a zynthian with an external aerial makes it sound very 50’s …