One of the less popular types of nixie tubes are the bargraph display tubes. The part numbers are IN-9 and IN-13. What’s nice about these tubes is that you can get a continuous bargraph display — it makes a nice alternative to a discrete LED display. People have used them in VU meters and similar circuits.

The IN-13 is the easier of the two tubes to drive, and it’s surprisingly simple. The hardest part is that you’ll need a good 150 VDC supply to power it. I build a little boost converter that runs off 12vdc to provide the 150 VDC. The control the indicator, a simple transistor driver is used using a MJE340 transistor, a resistor, and a pot.

Note that R4 and C1 are only necessary if you’re using a microcontroller that does not have analog outputs (such as the propeller). My goal is to interface the display to a a prop microcontroller so I can use it as an indicator in a few projects. So far, I’ve used a simple PWM output circuit to drive the transistor. Below is a youtube video:

An oscilloscope is one of the handier pieces of equipment that you can have on your workbench, especially if you’re working with circuits that generate any kind of waveform or have any sort of oscillators. For about a decade I’ve had a decent B&K precision 20Mhz analog scope. I felt it was finally time to try upgrading to a digital storage oscilloscope.

There were several options for inexpensive digital scopes. The first I looked at was the Instek GDS-1000 series, but I quickly found that much of the discussion of the Instek scopes also included comments about the Rigol units so I started looking into those. I found many positive reviews of the DS1052E.

I went ahead and ordered one from an Ebay seller who was also a registered US Rigol dealer. There used to be a lot more Ebay sellers (most of them unregistered, not official dealers) and the prices were more competitive, but the powers that be have clamped down on that, so expect to see only a few Rigol scopes on ebay. Other options include buying the scope from overseas (i.e. dealextreme or similar companies), but that can incur a lengthy shipping delay from China or Hong Kong.

The scope arrived double boxed and in good shape. It included a couple decent 1X/10X probes, power cord, CD, etc. One early point of confusion was the included Ultrascope software which had some installation problems. The ultrascope software requires the National Instruments VISA runtime (aka VISA32.DLL) and Rigol foolishly included a version of the runtime that was either broken or otherwise included an incompatible DLL file. Some googling revealed the correct version of the NI runtime could be found at http://joule.ni.com/nidu/cds/view/p/id/1071/lang/en. One expects Rigol will fix the installation CD to have a compatible runtime, so if you order your scope, hopefully the problem will be fixed.

The scope itself is a pleasure to use. It has a color screen, so the two channels appear in different colors. It’s capable of performing a variety of automated measurements (frequency, period, min/max V, peak-to-peak V, etc). It can save waveforms to external storage (USB card) which can then be recalled later or viewed offline on the ultrascope software. There’s really little to say about a scope… it does what it’s supposed to do, and it does it well.

It’s also very compact, using a fraction of the desk space that my old analog B&K did.

One of the interesting things about this scope is that posts on the ‘net claim that it can be software upgraded to 100 Mhz capability. I’m haven’t tried the process myself, as I haven’t yet encountered any signals that need that capability, but if you need a 100 Mhz scope, google around and look into the process yourself. I wouldn’t be surprised if the process was unauthorized and voided the warranty or otherwise brought down the wrath of doom upon you, but let’s face if Rigol didn’t want people soft-upgrading the scope then they should have thought about that ahead of time…

In summary, the DS1052E is a good scope. It does what it’s supposed to do. It does it well. It does it in color. I have no complaints.

Link to the youtube video:

Show the configuration:

show config
! to show running configuration instead:
show running-conf

Save the active configuration to startup config:

copy running-config startup-config

Show the access lists:

sh ip access-lists

Editing an access list for telnet access:

!using netmask 198.0.0.0 as an example
config
  ip access-list standard 23
    permit 198.0.0.0 0.0.0.255
    exit
    ! use 'no 10' to delete the original acl
  exit

Changing the router’s IP address:

!Changing router IP to 198.0.0.108 as an example
ip dhcp excluded-address 198.0.0.108
ip dhcp pool ccp-pool
  default-router 198.0.0.108
  exit
interface Vlan1
  ip address 198.0.0.108 255.255.255.0
  exit

Setting up DNS proxy and name servers to point at comcast:

ip domain name lan
ip name-server 68.87.69.146
ip name-server 68.87.85.98
ip dns server

Setting hostname for the router:

hostname scottsrouter

Setting local DNS entries

!puts smbaker4.lan and smbaker4 at 198.0.0.54
ip host smbaker4 198.0.0.105
ip host smbaker4.lan 198.0.0.105

Changing the SSID of the router from ‘CISCO’ to ‘NETGEAR’:

interface Dot11Radio0
  ssid NETGEAR
    authentication open
    guest-mode
      exit
    exit
  exit
dot11 ssid CISCO
  no authentication open
  no guest-mode
  exit
interface Dot11Radio0
  no ssid CISCO
  exit

Enable SNMP monitoring:

snmp-server community public ro
access-list 60 permit 198.0.0.0 0.0.0.255

Port-forwarding:

! Let's assume you have an internal web server on 198.0.0.123 port 80
! and you want it to be externally visible on port 8080 on the router
! and your WAN interface is FastEthernet4
ip nat inside source static tcp 198.0.0.123 80 interface FastEthernet4 8080

Show port-forwarding

! This will dump the whole NAT table. If you configured static port forwarding, then
! you ought to see your entries in there somewhere.
show ip nat translations

Useful SNMP variables:

useful snmp variables:
  new cpu:
    5s cpu use: 1.3.6.1.4.1.9.9.109.1.1.1.1.6.1
    1m cpu use: 1.3.6.1.4.1.9.9.109.1.1.1.1.7.1
    5min cpu use: 1.3.6.1.4.1.9.9.109.1.1.1.1.8.1
  older ones:
    5sec: 1.3.6.1.4.1.9.2.1.56.0
    1min: 1.3.6.1.4.1.9.2.1.57.0
    5min: 1.3.6.1.4.1.9.2.1.58.0
  memory:
    pool name: 1.3.6.1.4.1.9.9.48.1.1.1.2.x
    pool used: 1.3.6.1.4.1.9.9.48.1.1.1.5.x
    pool free: 1.3.6.1.4.1.9.9.48.1.1.1.6.x
    where x=1: processor, x=2: io
  using snmpwalk:
    snmpwalk -Os -c public -v 1 198.0.0.108  1.3.6.1.4.1.9.9.48

See Also:

• Scott’s Router Monitor. A small tool for monitoring Cisco routers. Works with my 861w. Don’t know if it works with other routers. Displays packets in/out, cpu util, and memory util.
• Review of the Cisco 861W. My review of the router.

The rubber on the wheel just sort of disintegrated. It wasn’t from use. It was just old. Apparently the wheels on Nordic Track Elliptical machines like the CX 985 only last about 5-7 years and then they spontaneously disintegrate. Never fear, Nordic Track is a good name, I ought to be able to order a replacement wheel, right? Well the nordic track website reveals that replacement wheels cost…

$ 83.95 per wheel

Yep, that’s right about eighty-five bucks for a replacement rubber wheel. The machine takes four of them. If one is bad, you can be all four are about ready to give out. A total replacement cost would be about $335. That’s well over half the cost of the entire machine when it was new. Four cheaply built, poorly constructed wheels cost over half the cost of the machine. They’d probably go bad in another 5 years, if they even lasted that long. Looking at these wheels, they’re nothing special. The bearings are standard $1.50 bearings (sold at the Nordic Track store for $9.50). I can guarantee this wheel could be sold at a profit for around $8, not $85. That’s a 1000% markup for us good loyal nordic track customers. No thank you, this is the last nordic track machine I will ever buy.

In search of replacement wheels, I found several sources online. It turns out that inline skate wheels are approximately the same size. Inline skate wheels can be had for $15 or so. The ebayers will often list them for around $30 each as “nordic track replacement wheels”, because they know you’re frustrated from the $85 sticker shock and thirty bucks sounds like a bargain.

Okay, so we’ve found a source for replacement wheels…. nordic track failure-wheel is on the left, inline skate wheel is on the right:

… unfortunately the CX 985 uses bearings that have a 3/8″ inner diameter. All of the inline skate wheels have 5/16″ inner diameter. You can’t fit a 3/8″ bolt in a 5/16″ hole. This probably isn’t the case for most Nordic Track machines; I seem to be one of the unfortunate consumers who ended up with a machine with the weird size. If you have any question what size yours are, just take the broken wheel to the local hardware store. If a 3/8″ bolt fits in it, it’s 3/8″. If a 5/16″ bolt fits in it, then it’s 5/16″.

Note: If your machine uses a 5/16″ bolt, then you can skip the whole remainder of this guide. Just mount your new wheels in place of the old ones. You might need a slightly-longer bolt if the wheel hubs are wider than your original. (well, you can still read the rest of the guide to laugh at my misfortune in having to deal with the improperly-sized bearing)

So, we’re faced with a couple of options. One option is to swap the bearings. The old bearings almost fit in the new wheels, I could probably force …err I mean press… them in. However, the inline skate wheel has a funky little spacer in the middle of it that is also too small for my Nordic Track bolt. The next option is to use a 5/16″ bolt and a sleeve to make the smaller bolt fit the larger diameter hole in arm of the Nordic Track (without a sleeve, the small bolt would sit sloppy in the machine). What I needed is a sleeve that’s 5/16″ on the inside and 3/8″ on the outside. Here’s a picture:

You can see the nordic track bolt on top, and my bolt and sleeve on the bottom. Note that I would have preferred a grade-8 bolt and probably will substitute one as soon as I can locate one. My local hardware store only had 3″ grade 8s, and I needed a 4″. It looks like a nice little bronze sleeve bearing that I found, doesn’t it?

Well, it isn’t… 3/8 x 5/16 sleeve bearings are kinda hard to find, especially on a Sunday. I’d probably have to order one. So, I took my bolt to the hardware store and search for something of the proper dimensions. What I found was …. copper plumbing tubing:

This was 3/8″ OD pipe. It says it’s 1/4″ ID. However, it’s not. It’s really 5/16″ ID. The pipe manufacturer probably figured they could save a few bucks by making the walls of the pipe just a wee bit thinner. If you go the same route as me, make sure to verify this; I don’t expect that all copper pipe is of the exact same dimensions as mine. It’s amazing just how perfect the fit was. An engineer will tell you that copper pipe != bronze sleeve bearing. Well, we’ll just have to see how well it holds up. It’s tight enough and the rest of the parts have ball bearings, so I bet the little copper sleeve will suffice for the life of the machine. If I’m wrong and my elliptical machine self destructs, I’ll be sure to let you know. Anyhow, here’s a picture of the sleeve installed in the arm of the Nordic Track CX985:

It just took some light sanding and a little tapping to get it to fit tightly in there. We now have a 5/16″ arm, a 5/16″ bolt, and 5/16″ wheels. All we need to do is assemble them:

Look at that, total cost was nineteen cents for the bolt, eleven bucks for the pipe (with 9 feet 11 inches left over), thirty bucks for the pair of wheels = $41.19. If I’d bought the wheels from the Nordic Track store, this would have been 167.90, not including the bolt.

So far it’s working good with one exception. It squeaks just a little bit. Kinda like there’s an unfortunate cat caught up inside of the mechanism. The squeak is nothing to do with the bearings or the bolt or the pipe, or anything I did, but rather is the side of the wheel rubbing against the the sides of the track. As you can probably tell in the above pictures, the wheels sit just a little bit wider than the original nordic track wheels did and their shape is just a little more rounder than the nordic track wheel, which had a flatter profile. A tiny bit of grease applied to the side of the wheel has stopped the squeaking. We’ll see how long it holds up.

Well, that’s all there is. Unfortunately, Nordic Track’s excessive greed in the price of the poor quality rubber wheels has led me to no longer recommend their equipment. Nordic Track elliptical machines are officially on the do-not-buy list. I could understand a 20% markup, or even a 50% markup, but a ONE THOUSAND PERCENT MARKUP is ridiculous. It’s a massive ripoff of the consumer who unfortunately placed his faith in what was supposed to be a quality-built machine.

Oh … and just to make things interesting… the inline skate wheels had little LED lights inside of them, so now my elliptical machine lights up at night… unexpected feature? or annoying blinky thing? you decide!

Unpacking:

First of all, unpacking…. It comes in a big box, and it’s relatively heavy. Big heavy things are the sure indication of a quality product, right? well let’s hope so.

Using Cisco CP Express:

The router comes with a CD-ROM containing installation software. There are several ways to configure the router, ranging from command-line terminal sessions, to something called CP Express, and to something even better than CP Express called simply “CP”. The quick start recommends using CP Express, so I go with that.

It needs a password. Well gee, that’s the one thing Cisco forgot to write down anywhere. Searching the printed documentation that came with the router, I got lucky and found the following in the Cisco Regulatory Compliance and Safety Information Roadmap:

The default username and password is Cisco. They are case sensitive.

Well, they were almost right. It is case sensitive, but it’s “cisco”, not “Cisco”.

Okay, back to business. Now we have CP Express up and running and it’s asking us questions that sound like the usual things a router asks: what IP address do you want to use, how do I connect to the WAN, what DHCP settings to use, etc. This all seems very good. I get it all configured and press the magic <Ok> button at the end. It tells me it’s updating the router configuration and exits. It does not update the configuration. No settings are changed. Try it two or three times more, no difference.

Using Cisco Configuration Professional:

So, I move away from the toy “CP Express” to the much more ominous-sounding “CP”. Who wants the use the “express” version of the software, anyway? We’re professionals here.

Well, CP loads up, displays a progress bar, opens two Windows Explorer windows, opens a third thing off screen, and sits there. I go off to the kitchen and get a bite to eat. It’s still sitting there. I watch some youtube. Still sitting there. Progress bar keeps moving across the screen (who was it who first decided progress bars should move even when the software is stuck, anyway?). It’s obviously not doing anything.

Maybe it has something to do with that window that’s 95% off-screen. I open up the windows task manager and start killing processes until I figure out which one it is. It’s called “IEC2″ . I don’t know what it is or what it does, or why it’s 95% off the screen. I can’t move it. I try to get clever and resize the screen but that doesn’t work either. I reboot the laptop again. Still stuck with a progress bar that indicates progress even when no progress is happening.

Took a break…. played some warcraft… did some work….

The next step I setup a virtual machine to run the Cisco CP software in so that I could try to configure it from a controlled environment. On a plain ordinary windows XPSP2 VM, the CP tool also failed. After wasting another hour scouring the Internet, I realized that this thing needs a particular version of Adobe Flash installed. Yes, that’s right:

YOU NEED ADOBE FLASH TO CONFIGURE THE ROUTER

If you don’t have flash installed, does the CP software warn you? No. it just sits there with a blank screen. If that isn’t pure stupidity, I don’t know what is. You also need java, which is slightly more understandable, but also a pain in the butt.

So, now we’ve got the CP software installed, running, and able to detect the router.

The next step, I try to enable the internal access point. It acts like it configures it, but the AP is not visible from any wireless devices. Don’t know what’s going on there.

Next, I try to change the router’s default IP address from 10.10.10.1 to something more sensible. Software warns me that it’ll lose connection if I change the IP address (well, duh!, but thanks for the warning). After changing the IP Address, the software immediately hangs. While it was smart enough to warn me that the connection will drop, it seems that the CP software itself isn’t smart enough to realize this and hangs waiting for a reply from the (now at a different address) router. Eventually after a few minutes it’ll time out.

Unfortunately now it can’t talk to the router. Although the router is at the new IP Address and responding to pings, it doesn’t respond to telnet or web connections. Could it be that I need to write the configuration to flash and restart the router to restart telnet and web on the new IP? I don’t know, and I’m a little bit worried about bricking the router if I write a known bad configuration to flash.

Fixing the access-control list:

Got out the serial cable and a USB-to-serial adapter to try to figure out what the heck was going on with the router that refused to talk to the new IP address.

The answer was fairly simple once I examined the configuration. There’s an access-control-list that specified which IP addresses are allowed to access the telnet and web interfaces. The ACL was not updated when the router’s IP address changed. Therefore we had a router that was configured on one network, but only allowing connections from a different network. The fix was fairly straightforward — from the serial terminal:

config
ip access-list standard 23
permit 192.168.0.0 0.0.0.255
exit
exit


The above is of course for a network 192.168.0.0 with a netmask 255.255.255.0. Note that the second argument to the permit directive is sort of the inverse of the netmask — it’s a mask of clients that you wish to allow.

Once I proved the router was working and talking to everyone I expected it to, the next step was to write the configuration to the startup configuration, so the router would be setup correctly on power loss:

copy running-config startup-config

Getting the access point up and running

Okay, so now let’s have a look at the internal access point.

The AP works like a separate device inside of the same box. It has it’s own IP address. It has it’s own configuration file. If you follow my CLI examples below, make sure that you’re telnet’d into the AP and not into the router.

The access point gave itself an IP address using DHCP. I don’t like dynamic IP addresses for my access points, so for our first step, let’s change it to a static IP. I used the CLI for a quick change (make sure you telnet into the AP, not the router):

config
interface BVI1
ip address 192.168.0.123 255.255.255.0
exit
exit

(of course, the telnet connection drops when we do this, because we just changed the IP address. We’re smart enough to know this, even without Cisco CP to warn us)

Ok, just as an example, we see the internal AP now set to 192.168.0.123. Simple enough, I’m starting to like the CLI way more than the crappy GUI tools.

Now lets play along with the GUI interface to the access point. Surprisingly it doesn’t suck the CPExpress and CP did. We can get to the GUI by using the IP address of the access point (in my example above, 192.168.0.123; probably different in your environment) in our web browser. It’s a much simpler design than CP/CPExpress. It doesn’t have the ridiculous pop-up window, and I’m guessing it doesn’t need Adobe Flash to work.

The AP will ask for a name and password. Even though I set the username and password on the AP, and verified it was set to what I wanted using the CLI, the access point GUI still expected a name and password of “cisco”. I couldn’t find any place in the GUI to change this. So, let’s fix this, again using the CLI on the AP (make sure you telnet into the AP, not the router):

config
ip http authentication local
exit
exit


I kinda figured this out by looking at the router’s configuration file, which had way more stuff in it than the AP’s configuration file. My guess was that since the ap lacked a ‘http authentication’ setting, it was defaulting to cisco/cisco. Telling it ‘ip http authentication local’ configures the http server to use the local username and password for authentication, which I think is what everyone wants.

Ok, back to the AP GUI. Like I said, it doesn’t suck as bad as the other cisco GUIs. In fact, it’s downright usable. You can click on the ‘express security’ link and setup your SSID and WEP or other authentication.

The wireless radio by default is disabled. You’ll want to change that. It can be done in the GUI by clicking network interfaces (notice Radio0-802.11N is ‘disabled’ and ‘down’). Then click Radio0-802.11N. Then select the ’settings’ tab. Click the ‘enable’ radio button. All the way down at the bottom of the screen is an ‘Apply’ button. Congrats, we’ve just turned the AP on. We can get out our laptop, check the WiFi, and find a new network available.

Now, once all of this is working, it’s time to save it to the startup configuration (make sure you telnet into the AP, not the router):

copy running-config startup-config

Observations on Day 2

Okay, we’ve made some progress and I think I have enough experience to make some conclusions:

1. The Cisco CP and CP Express software are junk and have major usability problems.
2. The Cisco AP web GUI is usable with some minor flaws.
3. The Cisco CLI (command-line interface) is by far better than any of the GUIs.
4. The Cisco CLI is easy to learn, at least for someone with average experience to command-line operating systems (and by ‘average’, I mean I’ve been doing this for 25 years).

I would suggest that anyone who wants to use one of these routers invest some time in learning the CLI. Although I figured out what I needed to do by stumbling around and the occasional google query, it might be handy to pick up a book and read up ahead of time. So far the router feels more configurable and more powerful than the other routers that I’ve used (D-Link, Netgear, Linksys, and DDWRT). It’s going to take some time to learn the full potential of what I can do, and how to do it.

For a very quick intro to the Cisco CLI, I’d recommend this link: http://www.cisco.com/warp/cpropub/45/tutorial.htm. It helped me considerably with some of the simple commands like setting IP addresses, writing the startup configration, etc.

Setting up a DNS proxy

All of my other routers had a DNS proxy built-in. The local computers send DNS requests to the router, which forwards those requests upstream to the ISP’s DNS servers. There’s a variety of flavors of this from simple forwarding to caching to actually running a local DNS server.

Scouring CP and CP Express for this (why did I try the GUI tools again? why?) there’s no explanation for how to set this up on the Cisco router. Some googling reveals some simple CLI commands can be used to setup the DNS proxy:

config
ip name-server 68.87.69.146
ip name-server 68.87.85.98
ip dns server
exit


Note that 68.87.69.146 and 68.87.85.98 are comcast’s DNS servers for my area. You’ll want to substitute the DNS server addresses for your ISP. There should be a way to learn the ISP’s settings from DHCP, but I’m not sure how — if somebody knows, please reply to this post.

Observations at Month 1

It’s now been about a month and the router has performed pretty much flawlessly. I even took some time to experiment with snmp monitoring and wrote up a SNMP monitoring tool for windows.

Related Stuff

• Scott’s Router Monitor. A small taskbar application to monitor Cisco routers. I wrote it because I didn’t much care for the web-based monitoring tool that came with the router. The tool will show you packets in/out, cpu utilization, and memory utilization.
• Cisco Router Cheat Sheet. Snippets of useful IOS stuff.

youtube video of my demo of the AOYUE 852A:

youtube video of an extreme close-up relflow soldering a part using zeph solder paste:

Curiously the book was available at Barnes and Noble in their ebook format. Now, I already suspected that B&N and Amazon products are not compatible. You can’t read B&N books on a Kindle. They use something called Digital Rights Management, or DRM. Every attempt at DRM has been a miserable failure, and this is no exception. Customer wants to buy the product but can’t use it. Trivial processes exist on the web for defeating the DRM. The DRM only succeeds in impeding commerce and causing customer frustration.

However…. for those with a little technical savvy there are some tools that can help. A Linux program called “eRdr2Pml” can extract the ebook text from the B&N PDB file and turn it into a PML file. A program called “Calibre” can take that extracted PML file and convert it into a kindle ebook. It’s only two quick steps to turn a Barnes and Noble book into something that can be read on the kindle. “eRdr2Pml” is a python program, and as such is probably easiest to get going on Linux. If you’re a windows-only user whose knowledge is limited to knowing how to point and click on things, then you’re probably going to have to wait for a simpler solution or do some more googling than I did.

I’m not going to provide download links because there’s no need to offend the legions of DRM-enforcing lawyers that these companies employ. You can google for these tools yourself. Oh and this post is completely hypothetical and made up and a total fiction and I in no way removed the DRM from a DRM-protected file.

Finally, I want to state that piracy of ebooks should be avoided. The authors have put a lot of time and effort into their writing, and they don’t need their works stolen. If you want to read the book, pay for the book. Don’t make copies of the book for other people.

Sourcing Componets -

Gyroscope: GWS-PG-03, Power Hobby
Accelerometer: LIS3LV02DQ, Newark Electronics
Accelerometer Proto-Board: Proto-Advantage
H-Bridges: (2) LMD18200, ebay
H-Bridge proto-boards: Spark-fun electronics
Main Board: Parallax Professional Development Boards
Motor: GHM-16, Lynxmotion
Motor Mounts: Lynxmotion
Motor Rotary Encoder: Lynxmotion
Wheels: Lynxmotion
Robot Chassis: Round alumininum, approx 8.25″ diameter x 3/8″ think, from the junk box at the local metal place.

A couple of the components needed special attention. The LIS3LV02DQ is a SMT package in QFN28 package. I used a proto-board from proto-advantage to adapted it to the usual 0.100″ spacing, soldering it with my hot-air gun. The LMD18200 also isn’t breadboard friendly, but some breakout boards from sparkfun electronics solved that.

The first step was to build the platform that the robot would sit on. I found a nice round chunk of aluminum approximate 8.25″ in diameter in the junk box at the local metal supplier. It was a little thicker than I wanted, but otherwise fit the dimensions and only cost me two bucks. Made a template using SmartDraw to figure out where the motor mounts would go (and get them square and true), and mounted the motors and mounts to the platform:

Next, I secured the Propeller Professional Development Board to the top of the platform using a couple of wood blocks. The PDB is only temporary; I’ll probably make a custom board eventually. Constructed a battery bracket from some more aluminum. A couple of pieces of aluminum flat stock were used to make some guard for the PDB so it wouldn’t get smashed if the robot crashed into something. Here are a couple pictures of the initial prototype of the robot:

Finally, here is a picture diagramming the major components:

Finally, a link to the youtube video:

This accelerometer is a 3-axis using and can communicate digitally via I2C or SPI. It can be interfaced to the prop with no external components (well a couple of bypass caps are usually a good idea) which make it pretty easy. It’s cheap, about $10/chip from newark. The problem is…. it’s a 28-pin QFN surface mount package, and I’m not a surface-mount person. The QFN package does not have pins; it just pads underneath the chip. This makes it a little more troublesome to hand-solder than some of the other SMT devices that do have pins.

So, it seems like the appropriate time to dive into surface mount work. I started by getting a hot air gun, an Aoyue 852A++ rework station for sra-solder.com. It cost $139 plus shipping, which came to just over a hundred and fifty bucks shipped. Seems like a bargain. The hot air station is chinese made, but the brand has good reviews on amazon and elsewhere. It features digital controls and also sports a built-in vacuum pickup tool. Here’s a picture of the rework station:

Above is a picture of the station sitting on my very cluttered workbench. There’s two toggle switches. One is a master on/off and the other switches between hot air and cooldown modes. The buttons are used to adjust temperature.

In order to breadboard the accelerometer, I got some QFN28-to-DIP adapter boards from Proto Advantage. These are little circuit boards with the QFN28 pattern on the top and a DIP pattern for standard 0.100 headers on the bottom.

I started by applying some solder to the pads on the board. Cleaned it up a little bit to make sure that I didn’t bridge any of the traces. Applied some flux to the board. Set the QFN28 chip on the board using some tweezers and aligned the pins as well as my eyesight permitted.

After that, I fired up the hot air station to 400 degrees with an air setting of about 12. Start swirling around the chip with the hot air until you notice the solder start to melt and flow. Shut down the hot air and let everything cool. It’s as simple as that. I didn’t record the time, but I’d say it took under 30 seconds to do the job.

To finish off the Proto-Advantage board, you have to solder the 0.100 headers on the back side. If I’d had some solder paste I think this would have also been a near-instant process. However, all I had on hand was my usual rosin-core throughhole solder, so I hand-soldered the 0.100 headers with my xytronic iron. Here is a picture of the finished product:

Although it kind looks like there are pins in the picture, looks are deceiving. The proto-advantage board has extra-long pads (probably to allow hand-soldering with a regular iron), and you’re seeing the excess solder the flowed out from under the chip back onto the pad. If I’d have used a stencil and solder paste, there probably would have been a lot less excess.

As you may notice, I soldered the chip about 180 degrees rotated from how I probably should have soldered it (the proto-advantage text is upside-down if you orient the adapter with pin1 toward the top). Fortunately, it doesn’t really matter. I’ll just mark pin1 on the adapter with a white dot or some such thing. If that’s the biggest mistake I made on my first SMT attempt, then I’ll be happy.

The next step was to put this thing on the propeller proto-board and see how it works:

I have the three LED displays showing the acceleration on the X, Y, and Z axis respectively. The Z axis points straight up. The X axis runs from the bottom to the top of the proto-board, and the Y axis runs from the left to the right of the proto board. Although it’s indicating 99 (9.9G) on the Z axis, it’s actually measuring 1.0G; I capped it at 9.9 to fit the measurements on the 2-digit display. The X axis is reading 0.1G, probably indicating my computer table is not level. As you tilt the board, the numbers change in the predictable way.

Well that’s it for this post; my SMT attempt was a success. The Aoyue 852A++ hot air station was very easy to use, and I’d recommend it to anyone looking to experiment with SMT work.

The miniDIGI and miniAMP are the two little cards sitting on top of my CinemaTube. The pepsi can is shown for scale. Here’s a closeup of the MiniDIGI and MiniAMP without all of my extra junk:

The miniAMP is the card on top and is a class-D amplifier that take I2S digital audio signals and amplifies them for your speakers. You can use it in a four-channel configuration (four digital signals in, four speakers out) at 10W per channel, or you can use it in a bridged configuration for 20W per channel (two digital signals in, two speakers out).

The miniDIGI card is on bottom. It has two toslink inputs, two coaxial inputs, a toslink output, and a coaxial output. It takes the digital audio from your audio components (dvd/blu-ray, media player, etc) and outputs I2S digital signals for other products in the miniDSP family. It can also take I2S inputs and output them on the toslink/coaxial outputs.

By using just these two cards, we have an amplifier that accepts your digital input (coaxial or optical/toslink), amplifies it, and drives your speakers. It’s a nice compact solution. The real power would be obtained by adding one of the miniDSP cards which can be configured as a digital crossover or other functions, but that is territory for a future review.

My miniAMP and miniDIGI arrived direct from the manufacturer, shipped all the way from Hong Kong. To my great surprise, I ordered it on a wednesday and it arrived the following monday. That’s much quicker shipping than many products that I order locally here in the states. The boards are well-constructed and include standoffs and cables for chaining the boards together. A toslink cable is also included. The one thing that isn’t included is a power supply. You’ll need something capable of supplying 12V – 24V DC at an amp or two. I used a 22.5 VDC / 1.5 AMP power supply from my Roomba. Beware that the power connectors use the 2.5 mm barrel jack, which I found to be slightly uncommon — the 20-30 wall warts in my junk bin all used 2.1 mm connectors.

Getting the amplifier up and running took only a few minutes. I reconfigured one jumper to select my input (optical #1). It comes jumpered to automatically bridge the input to the output, so you could easily daisy-chain multiple units together (think of the possibilities; a separate amp for each speaker, connected by optical cables).

I connected the supplied toslink cable to my CinemaTube media player and the thing fired right up. It’s pretty close to being plug & play.

There are a couple of limitations that one should be aware of. The most notable is the lack of a volume control. There are two jumpers than can select any of four preconfigured gains (-3 DB, 3 DB, 9 DB, 12 DB), but that’s it. One answer is to control the audio from your source device. This works perfectly with the CinemaTube that I was using it with. Another option would be to use a post-amplifier volume control. The solution that the manufacturer likely had in mind would be to use one of the miniDSP cards inserted between the miniDIGI and miniAMP. The miniDSP cards have an optional input for a volume pot.

The real flexibility will come with adding a miniDSP card, and that will probably be one of my future projects. An interesting projects would be to use two sets of miniDIGI + miniDSP + miniAMP, build each set into a speaker, configure the miniDSP to function as a digital crossover, and have this fancy amplifier-embedded speaker contraption. Such a configuration would get pricey ($70/miniDIGI, $60/miniAMP, $99/miniDSP) but it would be pretty darn slick when it was all done.

In short, an impressive product.