IanFyffe.net

Atten ADS 1102CAL oscilloscope

 

Just though I’d make a quick post about the inexpensive scope I picked up last year before I started working on multicopters.  Sadly I don’t have any new information to add, but I’ll summarize my findings and provide some (hopefully) useful links below.

I was searching for a small digital scope for general purpose use so I wouldn’t have to keep hauling around and firing up my Tek 585A. I wasn’t real picky on specs, so long as it was comfortable up to a few MHz, and had support for USB interface with a PC.

Long story short, I ended up with an Atten ADS 1102CAL, which shares its hardware with the Siglent SDS 1102CNL. This is good news, since Siglent is a slightly more reputable company, and they also release firmware updates for their scopes (more on that later).

For a detailed review on the scope, check here (CML version with more memory) or here (siglent version).  There’s also a hardware teardown posted here.

There are lots of pages online complaining about bugs in this scope, but most of them are on older firmware.  Sadly, atten doesn’t offer firmware updates, and the only way to get the newest firmware for this hardware seems to be to install the Siglent firmware.  Details here.  I haven’t done this yet, but I’ll update this post after I try it.

For linux users, I also found a program called attenload which allows user to pull screenshots and data from the scope similar to the windows software that atten provided.

SSH with no password*, no username, and SSH host aliases.

Want to increase convenience at the potential expense of security? Don’t we all. Well here’s how to authenticate without passwords*, and make aliases for your hosts while you’re at it.

First of all let me get that * out of the way. While it is possible to set up ssh logins with no password at all using this method, I recommend using a password when creating your key pair. This will give one master password shared between all logins that only needs to be entered once per session.

First of all you need to create a public/private key pair. I’ll assume you haven’t already done this.

 user@machine:~$ ssh-keygen -t dsa -f ~/.ssh/id_dsa

It will prompt for a password. You should use one here, and use this key pair for several hosts. This would give the same password across all of the hosts. Or, you can just leave it blank. If you do that, then if anyone gets your private key file, they can access all of the servers that have your public key file. So especially if you leave the password blank, protect your private file! You should now have 2 files in .ssh/. One will be your private key (id_dsa) and the other will have a .pub extension. Now,

 user@machine:~$ scp ~/.ssh/id_dsa.pub user@remote_host:.ssh/

Then log into the remote host,

 user@machine:~$ ssh anotheruser@remote_host

And move the key into the authorized_keys file

anotheruser@remote_host:~$ cd .ssh 

anotheruser@remote_host:~/.ssh$ cat id_dsa.pub >> authorized_keys2

And set the file permissions, if the file didn’t already exist.

anotheruser@remote_host:~/.ssh$ chmod 640 authorized_keys2

and delete the .pub file

anotheruser@remote_host:~/.ssh$ rm id_dsa.pub

You can now log out of the remote host. Try logging in again, it should just ask for the master password. For subsequent logins, no password should be needed. Now, how about setting up an alias for the host name, and having SSH remember your login name? On the local system open the ~/.ssh/config file. Create it if necessary. Simply set up the aliases like this:

Host mybox 
User anotheruser # remote login, if different 
Hostname mybox.somedomain.com 


Host anotherbox 
Hostname anotherbox.anotherdomain.org 

Once this is all set up, you should be able to ssh mybox, and the system will automatically select user name ‘myname’ and use the DSA key pair instead of a password.

NAD C370 protection circuit repair (amp fails, goes into protection mode)

A C370 with a defective protection circuit generally fails in a specific way.  The amp will work fine when cold, but after being on for several minutes, the protection circuit will activate.  Power cycling will not help, unless the amp is allowed to cool fully before the next attempt.

Well if you found me by the google because precisely this happened to you, you’re in luck. I just repaired mine for the wonderful sum of 63 cents.

To perform this fix you need to be somewhat comfortable with a soldering iron, and be willing to take your amp apart. If you aren’t very good with an iron, you’ll want to read through some how-to pages elsewhere until you’re comfortable with replacing through-hole capacitors on a printed circuit board.

My C370 ripped apart on my workbenchSo it turns out the design issue with these amps is that NAD decided to put a hot-running diode right beside (touching!) some electrolytic capacitors in the protection circuit. The heat from the diode ages the capacitors prematurely, which causes their values to drift.  The new values tend to cause the circuit to activate unnecessarily.

The protection circuitLuckily, the fix is simple.  First of all, locate the protection circuit pictured above. As you can see from the picture, mine had some obvious heat problems. Nothing looks broken per se, but it looks nicely toasted, especially on the right side and top. To get it working again, I’d recommend replacing the three topmost capacitors. Their values are 4.7uF, 47uF and 10uF all rated at 50V. I wouldn’t get anything larger than 50V as I’m not sure if it would fit.

**edit: According to Stu in the comments below, some amps have 63V caps, so I guess slightly larger caps might fit. Either way I wouldn’t recommend replacing your capacitors with new ones of a lower value than stock**

For those who are interested, here is the schematic for the protection circuit:

NAD C370 Protection Circuit SchematicWith those three caps replaced, the amp should work fine. But in a couple years, those caps will die too. I found a great solution on a forum: move the diode to the other side of the board.  Warning: make sure you keep the proper orientation of the diode when putting it on the other side of the board.

Diode on the back of the boardNow apply power, hope there aren’t any sparks, and enjoy the music!

Tektronix 585A

Thanks to my local freecycle list, I just got myself a new oscilloscope.

Encoding CDs to multiple formats

I’ve recently wanted to rip some CDs to several different formats at once. Say a FLAC copy for the computer, and an mp3 for the portible. After some searching, Abcde (A Better CD Encoder) seems to be the best package on linux for this. It is based around a bash script that will do CDDB lookups, and then use cdparanoia to rip the files, and encode them in your chosen formats.
$abcde -o mp3,flac,ogg
Its as easy as that. You’ll have to change the settings in the config file. Its located at /etc/abcde.conf (obviously..). I uncommented and changed these:

LAMEOPTS='-V 0'

OGGENCOPTS='-q 6'

To set mp3 encoding at alt-preset-extreme, and ogg encoding at Q6.

I have also edited a little bash script I found. It’s available here. When run, it will make .m3u files for all mp3s in the current directory and all subdirectories. Just put it in your path.