Archive for the ‘Raspberry Pi’ Category

November 17th, 2013  Posted at   Raspberry Pi, Raspbian

I have an old 15 inch VGA monitor optimized for a 1024×768 resolution which I have not used for a while. I thought it would be great to use it with my Raspi because it is quite small size, old and it creates that “retro” atmosphere that I love. But the thing  is not as easy as it may seem. In this post I will explain how I achieved this.

The first thing you need is an adapter to transform from HDMI signal (Raspi output) to VGA signal (Monitor input). The signal must suffer a transformation because HDMI is a digital signal while VGA is an analog one. Be careful with those cheap wires that have just a VGA port in one end and an HDMI port in the other one. They are useless for our purpose. The adapter you need may look like this (please excuse the cat…):

vga_adapter

You can find one of this in many sites, Amazon or eBay for example. I  bought this one for around 12 €. This model is great because it has also a jack port to get the sound that may come from the HDMI signal. So this is my Raspi connected to the old monitor using the adapter I got:

Raspi using HDMI to VGA adapter

Now when you turn on your Raspi three different things could happen:

1) You see everything perfectly in your VGA monitor. You are a very lucky person and you are probably wondering why I am writing this post.

2) You see a resolution that is not good for your monitor or that you do not want and you cannot change it.

3) You do not see anything in your monitor.

If your case is not the first one there is work to do yet. By the way, in my case it was the second one using Raspbian and the third one using Berryboot. I will be using the Raspbian example. When I turned on my Raspi I got a message from my monitor saying that it had to use a 1280×720 “failsafe mode” resolution which did not look very good:

1280x720, not proper resolution

I lost like a third of the screen using this resolution and the image and text quality was very poor. There was no way to change this resolution dynamically.

So now is the time to introduce the Raspberry’s config.txt file. This file performs a basic configuration  when you turn on your Raspi and change its parameters would be like tuning the BIOS in a normal PC. So this file is the key to get our monitor working properly.

The config file is located at /boot/config.txt but if your case is the third one, and you cannot see anything on the screen, you can read the SD card in other PC and you will find the file at /.

You can find all the details, parameters and configurations for this file at:

http://elinux.org/RPiconfig

The problem is that setting the right parameter values depends on your hardware; your monitor, your hdmi-vga adapter and even your wire! You can spend much time tuning this file but here is the trick that worked for me:

There is one parameter called hdmi_safe that when enabled (hdmi_safe=1), it sets the proper parameters to maximize compatibility for HDMI. Reading from the RPIconfig site above:

hdmi_safe Use “safe mode” settings to try to boot with maximum hdmi compatibility. This is the same as the combination of: hdmi_force_hotplug=1, hdmi_ignore_edid=0xa5000080, config_hdmi_boost=4, hdmi_group=2, hdmi_mode=4, disable_overscan=0, overscan_left=24, overscan_right=24, overscan_top=24, overscan_bottom=24

If you type (or uncomment in some config.txt files) hdmi_safe=1, save and reboot you should boot using a 640×480 resolution:

640x480 proper but too low

Ok. That is a low resolution but it looks much better. So this “hdmi_safe” parameter did a good job. Now, to be sure of which parameters have been set, let’s use a couple of commands again from the RPiconfig site:

vcgencmd get_config int – lists all the integer config options that are set (non-zero)
vcgencmd get_config str – lists all the string config options that are set (non-null)

In my case “vcgencmd get_config int” returned the following:

hdmi_safe=1
hdmi_mode=4
hdmi_group=2
hdmi_force_hotplug=1
disable_overscan=1
overscan_left=24
overscan_right=24
overscan_top=16
overscan_bottom=16
program_serial_random=1
config_hdmi_boost=4
hdmi_ignore_edid=0xa5000080
temp_limit=85
force_pwm_open=1

And “vcgencmd get_config str” did not return anything.

Therefore the group of parameters enabled do not match the ones RPiconfig indicates when hdmi_safe is activated. That’s why I recommend to use vcegencmd command, to be sure of which parameters are really set. Now the only thing left to do is to change the 640×480 resolution to 1024×768 and remove the “padding” you can see in the image above.

The resolution has to be with the “hdmi_mode” parameter, and you can see its possible values in the RPiConfig site. I will show some of them:

hdmi_mode=1 640×350 85Hz
hdmi_mode=2 640×400 85Hz
hdmi_mode=3 720×400 85Hz
hdmi_mode=4 640×480 60Hz
hdmi_mode=5 640×480 72Hz
hdmi_mode=6 640×480 75Hz
hdmi_mode=7 640×480 85Hz
hdmi_mode=8 800×600 56Hz
hdmi_mode=9 800×600 60Hz
hdmi_mode=10 800×600 72Hz
hdmi_mode=11 800×600 75Hz
hdmi_mode=12 800×600 85Hz
hdmi_mode=13 800×600 120Hz
hdmi_mode=14 848×480 60Hz
hdmi_mode=15 1024×768 43Hz DO NOT USE
hdmi_mode=16 1024×768 60Hz
hdmi_mode=17 1024×768 70Hz
hdmi_mode=18 1024×768 75Hz
hdmi_mode=19 1024×768 85Hz
hdmi_mode=20 1024×768 120Hz
hdmi_mode=21 1152×864 75Hz
hdmi_mode=22 1280×768 reduced blanking

…(truncated)

As you can see the hdmi_safe configuration used hdmi_mode=4 which corresponds to a 640×480 60Hz resolution. I will change this value to 16 that corresponds to 1024×768 60Hz which is perfect for my monitor. As you can imagine, the “padding” thing has to be with the “overscan_left”, “overscan_right”, “overscan_top” and “overscan_bottom” parameters. If you see my config, it is curious that  the “disable_overscan” is set and the overscan is working. I will set the four parameters I mentioned to 0 because I do not need any padding. My final configuration will be the following (remember that now we have to disable the hdmi_safe parameter):

hdmi_safe=0
hdmi_mode=16
hdmi_group=2
hdmi_force_hotplug=1
disable_overscan=1
overscan_left=0
overscan_right=0
overscan_top=0
overscan_bottom=0
program_serial_random=1
config_hdmi_boost=4
hdmi_ignore_edid=0xa5000080
temp_limit=85
force_pwm_open=1

Now I am ready to set or copy this parameters to the config.txt file and reboot. Everything looks great and now my monitor starts a new life working with my Raspi.

1024x768 perfect

1024x768 desktop

I hope this post can help you out.

Enjoy.

August 16th, 2013  Posted at   Linux, Raspberry Pi, Raspbian

When I bought my Raspberry Pi I also ordered this tiny usb wifi adapter (TP-LINK TL-WN725N) in order to play with my raspi everywhere. I got this adapter because  I read it worked out of the box, it was cheaper than others and it supported WiFi-N. As you may guess I am writing this post because the first advantage, the out of the box one, did not work for me.

Raspi with TP-LINK WN725N

I read some forums and it seemed that I had purchased a newer version of this adapter, the TL-WN725N v2. It needs a different driver, the Realtek 8188eu, which is not included by default in the Raspbian distributed by the official web site of Raspberry Pi. So, to sum up, I was able to find the driver source code and now I have a wireless raspi. If you have the same problem with this adapter, read the following lines to obtain directly the .ko object and you will be done. If you want you can download the driver source code (link at the end), compile and install it on your own.

To make it work just download the kernel object (.ko) file which is the compiled module driver for the kernel. I will be updating this section for different kernel versions.

For raspbian image: 2013-07-26-wheezy-raspbian.img
8188eu.ko (Compiled in 2013-08) (Working in kernel Linux raspberrypi 3.6.11+ #474 PREEMPT)

For raspbian image: 2013-09-25-wheezy-raspbian.img
8188eu.ko (Compiled in 2013-10) (Working in kernel Linux raspberrypi 3.6.11+ #538 PREEMPT)

For raspbian image: 2013-12-20-wheezy-raspbian.img & 2014-01-07-wheezy-raspbian.img
8188eu.ko & firmware (Compiled in 2014-01) (Working in kernel Linux raspberrypi 3.10.24+ #614 PREEMPT & 3.10.25+ #622 PREEMPT)

For raspbian image: 2014-06-20-wheezy-raspbian.img
8188eu.ko & firmware (Compiled in 2014-06) (Working in kernel Linux raspberrypi 3.12.22+ #691 PREEMPT)

For raspbian image: 2014-09-09-wheezy-raspbian.img
8188eu.ko & firmware (Compiled in 2014-09) (Working in kernel Linux raspberrypi 3.12.28+ #709 PREEMPT)

For raspbian image: 2014-12-24-wheezy-raspbian.img
8188eu.ko & firmware (Compiled in 2014-12) (Working in kernel Linux raspberrypi 3.12.35+ #730 PREEMPT)

Place the .ko object in the following path:

/lib/modules/(your-kernel-version)/kernel/drivers/net/wireless

In my case it is the following path:

/lib/modules/3.6.11+/kernel/drivers/net/wireless

Last version of the rtl8188eu driver includes a firmware file called rtl8188eufw.bin you have to place this file under:

/lib/firmware/rtlwifi/

Now execute the following commands

depmod -a

modprobe 8188eu

We are done. You should see now the new interface (wlan0 normally) when the device is connected.

Driver source code: https://github.com/lwfinger/rtl8188eu

Enjoy.