The other night I happened to see a tweet come across my twitter stream from Joe Walnes (@joewalnes) about a resistor color code tool he created. You can find it at the clever domain resisto.rs. Type in a value and see what the proper color code should be. This is great for when you need to go searching through a pile of resistors and want to make sure you have the code right.
Nice job @joewalnes!
Also, you can fork the code from github.
Here’s a couple of quick tips to get around the Arduino IDE error message “Serial Port in Use.” These mostly apply to OSX, but since it is UNIX based, they may make sense for Linux as well.
Applies to: OSX, Linux.
The check to see if another process (like a previous run of avrdude) is holding the serial port open is easy on both Linux and OSX. Just open a terminal and run the command: lsof. The command will report back all files that are currently open by the operating system. UNIX-based operating systems do everything through files, so this command is useful to see what is keeping a serial device open. Since lsof gives a list of everything that’s open, and there are a lot of “files”, use grep to only list what is relevant.
The format of the command is:
[bash firstline=”0”]lsof | grep <device substring>[/bash]If nothing is returned, then that says no other processes are holding the file (or device handler) open. If one (or more) processes are returned, you can do some further investigation.
James-MBP2b:~ james$ lsof | grep usbmodem screen 68202 james 5u CHR 33,16 0t3418 783 /dev/tty.usbmodem24131 James-MBP2b:~ james$
Here we can see that the process “screen” currently has the serial port open. (Which I would expect, because I use screen in place of the Arduino Serial Monitor.) Which, by the way, looks like this on OS X:
JavaAppli 6570 james 48u CHR 33,16 0t562 783 /dev/tty.usbmodem24131
If you know the process shouldn’t have a hold on the device anymore, you can always make use of the kill command.
Applies to: OSX. (Maybe Linux)
If your installation of OSX is missing a writable lock file, you will get a Serial Port in Use error from avrdude, even though it isn’t. So if you run the lsof command from above and don’t see anything holding the port hostage, then do this quick check to see if the lock file is writable (or exists):
[bash firstline=”0″]ls -l /var/lock[/bash]If no file exists then run these two commands:
[bash]sudo mkdir /var/lockYou’ll be asked for your system password the first time (and then it is remembered for the second) because of the sudo command. You need temporary admin (root) privileges. The mkdir comamnd creates a directory or folder while the chmod command will set permissions. Feel free to click on the each of those links to verify what those commands do.
To be honest, I’m not entirely sure why this works. Personally, I do not have a lock folder and avrdude connects to my Arduino boards just fine. However, this simple fix has helped several people in the forums. Since it is pretty innacious, it might be worth an attempt!
These two fixes won’t always solve the Serial port issue. If you still get the “Serial Port in Use” error even though you verified nothing else is using it, then you might want to post in the Arduino Forums for a bit more help.
Fundamentally there are two types of voltage regulators: linear and switching. The names come from how they operate and how they achieve voltage regulation. Linear regulators tend to be a little cheaper to implement, but they aren’t as efficient as their more complex switching variants.
There are also some “cheap and dirty” methods that some designs use. Below is a brief description and example of each.
After getting a couple of flashing lights working on a microprocessor, the next fun project is generally building some kind of Matrix. At first I built a 5×5 LED matrix which was relatively simple to solder together. When trying to make one much larger, the task because significantly more complex. That’s when I decided to build a LED Matrix Shield for the Arduino which did not use Charliplexing, like the LoL shield. I wanted something that was simpler to understand and (ultimately) code for. Unfortunately, 5mm LEDs means 8 columns x 6 rows, instead of the traditional 8×8.
Digital ICs like microcontrollers, memory, and shift registers need a stable voltage source to make sure they work as expected. Most circuits are designed with a voltage regulator to accomplish this stability. In theory voltage regulators will vary their output to stay at a set voltage, regardless of how much current the load is drawing. As a load draws a little bit more current, the supply voltage will begin to sag. Conversely when the load is reduced the voltage may rise a little bit. Regulators work to eliminate, well minimize, this change.
Full Tutorial: Voltage Regulator Basics
