Author: Yazeed

if it is not checked on the back side, the simplest and fastest way to do this is to look at the resonator, (Clock) – usually a Crystal oscillator, but I don’t see why it can’t be a ceramic resonator, if it has something with an 8 in it, then it is probably an 8MHZ resonator, otherwise it is probably 16, where 8 comes with the 3.3V and 16 with the 5V (Scroll down to see an example)

Another way is to connect the RAW to, let’s say 12V or even 5V, and measure the voltage at the VCC pin, that would also tell you, but surely, this involves more than just looking at the board, you need to connect wires and a power supply !

mine reads 80 u (something that looks like the letter U) so it is 3v3, here is a photo

If your resonator does not read anything with an 8 on it, (My other one reads A.P), chances are it is 5 Volts

The CP2102 breakout board shown in the photo below has a selector between 3.3V and 5V.

In my case, i simply connected it the way you see it here to a USB port with 3.3V, and what do you know, it works, I have a flashing red light on the Arduino, a constant green light, and it looks like it is read to take code, the CP2102 board has a constant red light.

if you want to check that it is actually working fine, simply upload the sketch blink no delay, and then alter it a bit so that it does a double blink then wait 2 seconds, now your code is working, there you have it.

From the device manager, I can see that there is a device that looks like my adapter, namely this one

Silicon Labs CP210x USB to UART Bridge (Com3)

That thing above tells me that it has been designated the communication port number 3, which i will need in the Arduino IDE

So now i have installed and am running the Arduino IDE, selected a 3.3V Arduino board from the list and selected Com3, now i should be ready to upload a sketch, let us make a sketch that double flashes an LED every 2 seconds. here is some code to do that

To create a tiny power supply to turn a 5V power source into 3.3V for powering the ESP8266 or ESP32, or maybe an Arduino pro mini (3.3V version), all you need to do is to couple the LD33CV-LD1117V33 with a pair of capacitors, in my case I am using the 25V/100 uf capacitor

All you need to do is the following

connect one capacitor to the pins 1 (Vin) and 3 (GND), and the other to the pins 2(Vout) and 3 (GND), and you are done.

At this stage, the ones between 1 and 3 will receive the input 5V power, While the ones closer to each other (2 and 3) will have the 3v3 output voltage that you can connect directly to your Arduino or ESP micro controller

The LD1117V33 you see above (LD33CV) comes in a TO-220 package, and uses an NPN pass transistor for efficiency to provide up to 800ma of power (Cooling may be needed to achieve maximum)

Sometimes you need to find the largest sub directory in a directory, for this, the DU command has an argument that can work for you, max-depth

du -h --max-depth=1 backup-final

The above will simply list all sub directories inside the backup-final directory alongside the size of the directory (recursive, including all files in sub directories)

One of the most annoying things that can happen to you is to disconnect your laptop from the network, then realize that there was a file moving job that was running, the command is going to get disconnected before mv gets the chance to delete the source files, the new copy is a hassle, i personally use rsync to continue such a copy with the delete source files flag

But it does not have to be this way, you can move the mv command to the background, the steps are simple

First, to suspend the job, you need to hit CTRL+z , once suspended, you should see a job number in the suspend acknowledgement

CTRL+Z

Now, the next step is to disown the job, because right now, if you close your terminal window, the job will still be terminated

disown -h %1 (replace one with your own job number which may be 1)

Now to get the job running again but in the background

bg 1

That is it, you can now close (logout) your terminal window

So the summery
ctrl+z
disown -h %1
bg 1
logout

Now mind you, the output to stdout will not display (In most cases), you will need to use process status ps x to see the process.

If you want to bring back the command into the foreground, all you need to do is execute the command jobs (to find the ID), then run the command fg 1 (if it was job number one), then to hide it again, you can ctrl+z then bg 1 again (No need to disown it this time)

Sometimes, you realize you would want to use LVM in a computer but you want a tutorial to take you there fast, So i have put this post together to get you up and running in 10 minutes or less.

First, let us start with the tools, install the following packages in your debian installation, (Debian 10-Buster in this tutorial)

apt-get install lvm2 dmsetup mdadm reiserfsprogs xfsprogs

In this tutorial, I have two 8TB disks i want to combine with LVM to use as one

1- Create partitions of type LVM on the disks

• Why not use the disk without a partition ? See this post

Start by running parted on every physical disk, and creating a big partition to span the whole disk (Or if you are using empty spaces on old disks, any partition is good enough really)

In my example, where i wish to combine /dev/sdb and /dev/sdc into one logical volume (To be used as one block)

parted /dev/sdb
mklabel gpt
unit mib
mkpart primary ext4 1 100%
set 1 lvm on

Now, repeat the above, but this time for /dev/sdc

1- Prepare the physical volumes to be added to volume groups (those two partitions) (For instructions on how to add disks directly without an underlying partition which is not recommended, see here)

pvcreate /dev/sdb1 /dev/sdc1

Now, you can see what we have with the commands

pvdisplay or pvs

2- Add the PVs to a logical volume

vgcreate LVMGroup /dev/sdb1 /dev/sdc1
   Volume group "LVMGroup" successfully created

this will create a volume group (VG) called LVMGroup, you can see the VGs you have with the commands (vgdisplay, vgscan, and vgs)

vgs -o +lv_size,lv_name

3- Create a logical group on the volume group

lvcreate -l 100%FREE -n bigvol LVMGroup
  Logical volume "bigvol" created.

mkfs.ext4 /dev/LVMGroup/bigvol
or
mkfs.ext4 /dev/mapper/LVMGroup-bigvol

4- Mount, and add to fstab

To mount the volume, My mount point is at /hds/lvm

rsync is better than mv to move files because of a few reasons

First, it gives you much more control, for example the following command

rsync -a -v --ignore-existing --remove-source-files /hds/iscsi/all_new /hds/usb

Does not copy the files that are already at destination, meaning if there is a file with the same name in the same directory at the destination, it will not be overwritten, files moved will be deleted, and files that had counterparts and not moved will not be deleted

rsync -a -v --remove-source-files /hds/iscsi/all_new /hds/usb

While the command above will overwrite files, and delete whatever we have moved ! if files exist on the destination, it does not seem to be overwriting them, but it is probably somehow comparing them, then deleting the original

I had to investigate this as a move command resulting in an error did not remove the files, the error was relevant to the file name being too long

When tarring a file, even if the process (Nice) priority is low, sometimes the IO will make the computer unusable, so what you can do it ask Linux to only work on the IO intensive job when there is no other application requiring IO

ionice -c 3 -p $PID

The above class (3) means only if no other application is using this disk

The answer is, depending on your needs, but you are not here to hear that now are you, so I did a little experiment, tailored specifically for a certain need that does not apply accross the board, but combined with other experiments online, this might give you an idea

The experiment is annotating an image with image magic plugin for PHP

Both running buster (Debian/Raspbian 10), both on PHP7.3 and everything fresh installed

the PC has 8GB of DDR3 Ram, and the PI 1GB of LPDDR2-900 SDRAM

The PC has a 12 year old “Intel(R) Core(TM)2 Quad CPU Q9450 @ 2.66GHz”

The PC was around 7 fold faster than the raspberry PI 3 (the mean of a trial of 20 runs, with all the files cached in ram by the linux kernel)

The trial was done with a discrete VGA card (AMD RADEON) and with the chipset’s own graphics card, results were identical (The VGA card did not have it’s drivers installed, so we don’t know if it might have an effect or not)

I am now moving into even older PCs to compare performance, and will report the results here again to see what the limiting factors might be

Usually, i go with a serial cable, these days, people have found simpler ways

Start by downloading lede-17.01.5-ar71xx-generic-tl-mr3220-v2-squashfs-factory.bin from the openwrt website (Don’t use the original, it needs trimming 😉 and you can install it after using the post after this one

rename the file you downloaded to mr3220v2_tp_recovery.bin and put it in your tftp client folder

Setup your computer’s LAN settings to the IP address 192.168.0.66

Connect the eithernet cable to the yellow LAN port farthest away from the blue wan port (Not the one next to it, only this port works)

start your TFTP client, pick your eithernet LAN and connect the lan cable

Hold the WPS/Reset button, and while holding it, start the router, then wait 4 seconds and release it

On your screen, you should see your TFTP client sending a file (on tftpd32 you see a download progress bar)

Wait for the router to reboot, now you have hte openwrt firmware, go ahead and read the previous post on going back to factory 😉

Have a great day