MayorMike, inspired by the article I wrote for Make vol. 20 (Retro Wireless Handset), stuck a bluetooth headset in a plastic toy gun to create his Handgun Bluetooth Earpiece Project.  The best part – the earphone is located at the end of the barrel, so to answer a call, you stick it up to your ear.  Genius.

The innards are shown below.

Nice work, MayorMike!  May I suggest that you pair this with a Hand Grenade MP3 Player?

via BoingBoing

Gary Dion (N4TXI) created a Wifi Radio to match his entertainment center.  His project is inspired by my original Wifi Radio project and shares several of the same parts (such as the Asus WL-520gU wireless router) and design philosophy.

Interesting features of Gary’s version of the radio:

• Very cool 4 line VFD display allows more information to be shown at once (and it’s blue!)
• AVR sends actual shell commands to the router, which allows the serial console to remain enabled for debugging/other purposes – brilliant!
• Nice custom PCB for the ATmega8 microcontroller
• Rotary encoder and significantly more advanced control menus
• IR remote control support!

More details, photos, and source code are available on Gary’s site.

Thanks to the Make: blog for bringing this project to my attention!

Woot is selling a Samsung Bluetooth headset for $17.99 + $5 S/H – $20 MIR = $3 after rebate.

For that price this headset could be a great candidate to use for a DIY Retro Bluetooth Handset.

The catch is that I can’t guarantee this headset is actually hackable until someone buys one and reports back here.

Who will be the first?

Do you have a question about the Wifi Radio project or want help making your own Bluetooth Handset?

Try asking over at the discussion forums!

If you haven’t seen them before, be sure to check them out!

The rain and dropping temperatures in San Francisco this weekend reminded me of a project I made in the winter of 2006.  This was long before mightyohm.com existed, so I originally documented the project at instructables.  I’m not going to repeat everything here, but I wanted to share some pictures and provide a link to the instructable in case anyone else wants to try this at home.

The project involves using a digital programmable thermostat to control an inexpensive space heater.  The original motivation for this was that I wanted to lower the temperature of the heater at night, reducing my energy bill, while still being able to wake up to a toasty room in the morning by setting the heater to turn on full blast 30 minutes before I awoke.

Here’s a schematic of the simple circuit I made to interface the thermostat to the space heater.  The resistor/diode/capacitor circuit allows the thermostat, which is designed to control an AC load, to switch power to a 24VDC coil relay.  A 36VAC

I installed the necessary components inside the case of an old power and telephone line filter, used to protect a fax machine or office copy machine from power surges.  The case came with a handy 110V outlet mounted on the front panel which I reused for this project.  The digital thermostat mounts to the top cover of the case.

I used a barrier strip as a way to simplify the wiring and mount the few loose components:

I had to adjust the value of C1 to get reasonably clean DC to the relay while not having an annoying turn-off lag when the control line from the thermostat goes low.  100uF works well for the relay I used.

Here’s the finished product installed in my former bedroom:

I haven’t used it since I moved into a house with working central heating, but it sure came in handy during the cold winter I spent in a 100 year old farmhouse in Petaluma.  This solved the problem of the sub-50 degree mornings I was having nicely!

instructables.com: Space heater controlled by digital thermostat

Comments?  Questions?  Leave a comment below!

After thinking for a while about how to build the saw, I decided that it would be best to have the blade move only in the vertical axis, and the workpiece move horizontally in two axes.   This led to the overall machine design which consists of a vertical column with pivoting cutting head assembly, and a workpiece holder that has two axes of horizontal motion.

Completed Dicing Saw

I wanted to ensure the motor and blade had a rigid, heavy mounting structure to reduce effects of vibration and flex on cutting performance.  I decided to mount the motor using the original mounting flange from the hard drive enclosure since it was nicely machined to match the motor flange.  I used a hacksaw to cut out the shape roughly to size, then straightened up the edges and machined a mounting recess on my milling machine.  The L-shaped piece of aluminum is 1/2 inch thick which gives lots of weight and provides sufficient thickness for mounting the bearing while preventing motion orthogonal to the bearing axis.

Cutting Head Assembly

Another view of the cutting head assembly.  In the upper left hand corner is the pivot bearing.  The bearing is held in place with a set screw that goes through the L-shaped aluminum piece.  Along the bottom edge of the black hard drive enclosure portion I attached a strip of white LEDs to help light the work area.  RTV Siliconeis used to seal the electrical contacts from water that migt not be caught by the splash shield.  At the lower left hand corner of the aluminum plate is a rounded off screw.  The cutting depth adjustment micrometer pushes against this rounded off screw.  Pushing against the aluminum would be less accurate (aluminum would become unevenly worn).

Cutting head assembly (rear view)

At the top of the column on either side is a hole for the screws that hold the pivot bearing (also from a hard drive) in place.   Luckily the one I used has 4-40 threaded holes on either side.  A screw on each column holds the bearing in place, and then the rest of the column assembly and adjustment plate are attached resulting in a good alignment of the column to the bearing. 

Pivot bearing/column mounting detail

Controlling the depth of the cut is critical, as my cuts will be as small as 5 thousandths of an inch deep!  I mounted a micrometer head to a plate on the back of the column which controls the height of the cutting head assembly.

Rear view of the column and depth adjustment control

 Now for a little detail on the vacuum chuck… The chuck is made from two 1/4 inch plates of aluminum.  The top surface has a shallow set of trenches cut to distribute the suction across the bottom surface of the glass plate used for holding parts.  The lower plate has a deep trench cut in it to distribute the suction to the three small holes drilled on the top plate.  The whole thing is held together with screws and sealed with silicone.  I made a set of hose barbs (one is pictured below) so that I can use 1/8 inch vinyl tubing to connect to my vacuum pump.  The barbs were made by turning down 10-32 stainless steel screws on my lathe. 

Lower half of vacuum chuck with custom-made hose barb

  The last major component of the saw is the splash guard.  This actually took a fair amount of effort to make, as I broke pieces more than once and had to start over.  Essentially it is a two-piece design with a thick piece screwed to the cutting head assembly, and a thinner piece which screws onto the first.  I used a heat gun to soften the plastic and carefully mold it to the shape of the face plates.  I then glued the curved section and the outer face plate together using epoxy and while not very pretty, it holds together well.

Splash guard on the saw

10, 20, and 5 mil thick alumina substrates with 50 ohm transmission lines

In part 1 I gave an overview of what this project is all about. In this part I will describe the basics of the machine and some of the reasons I made the design choices I did. To start with, I wanted to do this on as small a budget as possible. The main project for which this machine serves ends up being a real money pit, so I have to budget accordingly. Hence the use of hard drive parts and scrap metal. Total spent so far is about $60.

When I first thought about how to cut these little pieces of ceramic, it seemed that there were a few elements that would be tricky on a budget. First thing I did was try and figure out how commercial dicing saws work. Certainly Intel and others have figured out a good way to slice ‘em and dice ‘em a long time ago… And they did.

Tricky thing #1: Holding the substrate while it is being cut.

After a wafer full of chips is finished being made, it is mounted onto a wide stretchy tape, creatively named “dicing tape.” The tape is pulled over a frame and then the wafer placed on top. Next the taped wafer goes into the dicing machine where it is cut by an insanely fast spinning diamond encrusted blade of blingy wafer death.

To keep the wafer from heating up (chips generally don’t like heat) water is sprayed at the cutting surface. This also helps to wash away crud generated by cutting and to prolong blade life.  Once the wafer has been diced into individual chips, the tape is exposed to UV light or heat. The adhesive on the tape is made to become less sticky when exposed, and at this point the chips can be easily removed with tweezers, or an automated pick-and-place machine.

My first thought was to try and get some of this tape and use it in the same manner, but for smaller pieces. Then someone at work told me about something far more cool, with a far better name, something called Crystalbond! Crystalbond is essentially a mounting adhesive designed for exactly what I want to do. You simply heat it up, it becomes liquid, place the part in the puddle, and then do nothing until it cools off and then solidly holds your part. I managed to find 5 lifetime’s supply on eBay for dirt cheap, but several other places sell it. Anyway after the parts are cut you wash it away with acetone and you are left with clean diced parts.

Tubes of Crystalbond mounting adhesive

Okay, so the part can be held, but I didn’t want to have to glue a part to my machine every time I wanted to cut something. So instead of gluing the part to the machine I decided to glue the part to small pieces of glass which are a convenient carrier and can be used with my hotplatethat I built for my wire bonder.

Hotplate for thermosonic wedge bonding

So now I’ve got a piece of easy to handle glass, with one or more substrates to dice which has to be mounted to the machine. I could use tape, a temporary adhesive, or clamps, but why? I just put together a digitally controlled vacuum pump for some composites work, so why not make a vacuum chuck? And even better, I mounted it to a precision X-Y dovetail slide that I purchased on eBay for cheap. Now I can easily position the glass, reposition if necessary, and make measured cuts my moving the X-Y stage and measuring at the same time with a runout gauge. This allows me to make cuts that are accurate to 0.001 inches.

X-Y positioner I bought off eBay

A note here regarding XY stages… I chose specifically a dovetail style positioner because unlike the more common linear bearing style slides, a dovetail slide has static loading.  The benefit is that there is a much greater resistance to vibration and since I am grinding, I want as solid a mount as possible.

Tricky Thing #2: The Blade

This is really a compound Tricky Thing, a combination of finding the blade, holding it, and spinning it. First a little background on dicing saws and blades…

Wafer dicing used to be done (and still is, especially in research situations) with a diamond scribe, basically a pencil with a diamond at the end. A small scratch is made along the crystal plane of the wafer and then carefully bent until a long, very straight crack is made through the wafer.

The same can be done with alumina substrates, although since it is not a mono-crystalline structure, the crack won’t be as straight or as predictable. Scribe dicing is a relatively labor intensive task and chip manufacturers HATE labor, but even more than that they REALLY HATE any time that an actual person touches a wafer.

Wafer dicing today is usually done with a very thin diamond abrasive blade that grinds away the metal or semiconductor until a cut is made. It is nearly identical to the way you might cut tiles when doing a counter top in your kitchen but on a much smaller scale. When cutting tile, if the blade wobbles a bit or is not centered perfectly, you are not likely to notice. With the alumina substrates I’m working with, the pieces are 20-40 times thinner. This implies that any vibration, wobble, or eccentricity errors can cause problems.

Commercial wafer dicing machines use high speed motors that are carefully balanced and rather than using ball bearings, employ costly air bearings. These are essentially out of reach for hobbyists and really not necessary. What is necessary though is a way to hold and spin the blade accurately. Dicing blades are thin, and the thickest ones I could find on eBay were 300 um wide. At 4.6 inches in diameter, a a very large inner diameter, they are also hard to accurately mount on a typical spindle like that found on a Dremel tool.

Diagram depicting blade mounting: Part A shows the original platter and spacer configuration, Part B shows the modifications I made, Part C shows the blade mounted.

All of these issues led me to use a hard drive motor and platters to spin and hold the blade. Hard drives have very long service lives and need bearings of the highest precision. The mounting of the platters is also done in a precise way, as any imbalance would shorten the bearing lifetime and result in undesirable operation.

To make a long story short, I removed (and reused) the spacer ring between the two platters of a hard drive, and reduced the radius of one platter to 3.5″, the inner diameter of the blade. You can see in the picture that the two platters are stacked and there’s a nice surface for gluing the blade down. Machining the platter down was not easy with my tiny lathe, and it ended up being out of round by perhaps 10 mils. It works to roughly locate the blade, but I will need to tack the blade down, measure, adjust, and finally glue into place. 10 mils out of round is really bad because the thickest substrate I’m working with is 10 mils thick. That means that one part of the blade would never actually do any cutting!

Blade test fitted to the saw.

Tricky Thing #3:  Driving the motor

This seemed to be slightly daunting at first.  Hard disk motors are typically some kind of brushless motor and require special circuitry to run.  I imagined that I would have to build a circuit, or use a motor speed control from a radio controlled plane, etc.  It turns out though that the main circuit board in the hard drive I’m using is dumb enough that even though it has had the equivalent of a frontal lobotomy, it just keeps doing it’s job.   A couple other hard drives I tore apart did not do this.

Motor Control Box

The box in the picture above shows the hard drive main circuit board and below that, a 12v/5v switching power supply.  It’s pretty basic and at the flip of the switch on the front panel, the DC supply is connected to the motor driver and voila, the motor spins up.

Schematic Diagram for the Motor Control Box

So here’s the background….I’m building a ham radio that operates at 47 GHz.  At such a high frequency there are very few components that can be soldered on to circuit boards, let alone components that even come packaged!  The easiest way to build a high performance radio at these frequencies is to use MMICs (Monolithic Microwave Integrated Circuits).   These are really just fancy, yet fairly simple circuits made from exotic materials, most commonly Gallium Arsenide (GaAs) instead of the usual Silicon used for normal chips.  Before MMICs were in widespread use, individual transistors had to be used, requiring delicate and hard to make external matching elements.  MMICs are like nice little 50 ohm building blocks.  Low Noise Amplifiers (LNAs), mixers, Power Amplifiers (PAs), phase shifters, etc. etc. are all available in this form.  Trouble is that you have to connect these pieces up to make a functional radio (or at least the microwave portion of it).

My WestBond wedge bonder

Wire bonding is the usual method for connection and is really just a method of welding a wire (or ribbon) from one chip to the next.  It turns out that you actually need space in between the chips, for thermal reasons, RF reasons, and for placing the requisite bypass capacitors.  So what goes in between the chips?  Well, coax cable is pretty much out, and most common circuit board materials start getting pretty lossy at 10+ GHz, and even the good stuff (PTFE-based usually) starts getting kinda lousy at 40+ GHz.   At very high frequencies, materials like ceramics and quartz become worthwhile.  In my radio I chose to use pre-made alumina ceramic substrates (tiny circuit boards).   These come with a gold layer on the back, and a gold line on top etched to perform as a 50 ohm transmission line (just like coax and just what the MMICs want to see).  I bought these with a number of other hams last year in a group buy.  They are fairly expensive being that they are 5 and 10 mils thick!

My first test bonds on an alumina ceramic substrate (ugly)

To make the best use of the sections that I bought I decided I needed to cut them to length.  Well how do I do that?  The thickest pieces are 10 mils thick (a piece of printer paper is 4 mils thick) and they are brittle!  Beyond cutting, how do I hold the piece while cutting and when it’s done?  The resulting pieces may be just 100 mils long, and 50 mils wide.   Obviously a pair of vice-grips simply won’t do.

So my first thought was a Dremel tool and tape.  This method could work, but it does not lend itself well to making measured cuts.  At 47 GHz, a few hundredths of an inch is a lot! Also, the available diamond blades for dremel tools are fairly wide and I wanted to waste as little of the  small substrates as possible.  At this point I made  a lucky find on eBay.

In the semiconductor industry, one of the last steps of making a chip is called “wafer dicing.”  After a wafer full of chips is made, they need to be cut out into individual parts.  To do this, wafer dicing machines were developed.  These are CNC saws that use a high speed (as high as 60,000 rpm) air bearing spindles with diamond abrasive blades.   They can cut lines across large dinner plate sized wafers that are as narrow as only a few tens of microns.   Luckily there is enough wafer dicing going on in the world that there is a source of surplus blades on eBay.  Not all blades are well suited for all materials, so do some research if you are interested.  Disco (a Japanese company) is one of the largest dicing blade manufacturers.

Large (4.6 inch diameter) wafer dicing blade in it's packaging.

While reading the last paragraph you may have spotted a few words indicating unobtanium.  Those words are “high speed air bearing spindle.”   Well I chose to use a hard drive motor instead, because they have excellent bearings and are readily availble  for free.  While they don’t move as fast, I don’t care.  I have a few short cuts to make, not millions of chips.

So that is an introduction to what I’m doing.  For the most part the saw has been built using surplus parts and remnant pieces of metal from my favorite local metal supply house M&K Metals in lovely Gardena, CA.   As of this entry, the saw is nearly complete, all that is left is the splash guards.  I’ll be posting the build of this project in several parts, so stay tuned.

And a link to my Flickr photo set for this project: Dicing saw

-Tony

Keith of Keith’s Electronics Blog made a PID-Controlled Soldering Hotplate based on the one I fabricated earlier this year.  He’s already using it to build the stepper controller PCB for the MakerBot CupCake CNC!

He also posted a bunch of teardown photos (like the one shown below) of the CD101 PID Controller from Sure Electronics.  I suspect the CD101 is a cheap knockoff of an RKC PID controller since I can’t find the part number on RKC’s website, even though the front panel clearly says RKC on it.  I guess at $40 you can’t ask too many questions, the price is right…

Copycat PID-Controlled Solder Hotplate « Keith’s Electronics Blog.

Recently I discovered that our local cable provider will soon be discontinuing analog cable service for most channels.   Because of this they are forcing encouraging customers to get new cable boxes and upgrade to digital cable.

I hate cable boxes.  More than just another piece of equipment to find a place for near the television, cable boxes waste power, always seem to take forever to change channels, contribute to the ball of wires behind the entertainment center, and add another remote control to the coffee table.

Most importantly, a cable box prevents our old Series 2 TiVo from being able to change channels directly, since it now has to negotiate with the digital cable box to receive TV signals.

TiVo provides a workaround for this – the infamous IR blaster.

I would love to meet the engineer who came up with the IR blaster.  Instead of pushing for a universal protocol to electrically connect cable boxes to things that may want to control them, some engineer came up with the incredibly stupid great idea to stick an IR LED in front of the IR receiver of the cable box and use it to simulate a handheld IR remote control.  The cable box thinks that the user is punching away at the remote (with lightning speed) while in reality a microprocessor is generating the remote codes and sending them to the LED.  It’s both ingenious, and at the same horrific in so many ways.  It grates against my engineering sensibility.  What manager approved this?

Back to the TiVo.  The IR blaster that came with our TiVo was lost long ago, in a time when no unnecessary electrical-optical-electrical sillyness was required for it to function.  Rather than spend $3 on eBay and wait a week to get a replacement, I decided to make one out of spare parts in my junk bin:

• an infrared (IR) LED
• a 1k resistor (not sure if this is necessary, safety first)
• a 1/8″ mono headphone plug with a couple feet of cable attached
• some heatshrink tubing
• duct tape

I don’t know if the resistor is required – the TiVo may already have an internal resistor.  I used 1k, if I see any problems with the cable box getting an intermittent signal I’ll try lowering the resistor to 330 ohms.

The tip of the 1/8″ mono plug is positive.  I connected the tip wire to the side of the LED with the longer lead (the side opposite the flat side of the LED).

I tested the circuit by applying 3-5V to the 1/8″ plug (tip is positive) and used my digital camera to check if the LED is working.  My camera has a decent IR blocking filter so I had to use nightshot mode to see it:

Finally, I put heatshrink over the LED connections and the resistor to avoid short circuits:

Back in the living room I plugged the DIY IR blaster into the jack marked ‘IR’ on the back of my TiVo.   A strip of duct tape to secures the wires to the bottom of the cable box.  I bent the LED up to point at the cable box’s IR receiver (the purple dot shown in the really bad photo below, sorry).

All that was left was to configure the TiVo using the cable box setup guide.  Within a few minutes I had my TiVo controlling the cable box.  The DIY IR blaster works perfectly!

Not bad for $0 in parts (all stuff from my junk bin) and a few minutes of soldering.

Steve Chamberlin created an 8-bit computer from discrete logic and called his project the Big Mess o’ Wires.

The BMOW runs at 2MHz and has 512K RAM and 16K ROM.  It is constructed with primarily 7400 series logic and over 1048 wirewrap connections.

The feature list is very impressive:

• It can multitask.
• It has VGA video output.
• It can make sounds and music.
• It even runs Microsoft Basic!

Here’s a video of a music test from his site:

I am completely blown away by this project.  Has someone invited Steve to the Maker Faire??  I want to see this thing in person!

Check out his site and prepare to spend at least an hour looking at all of his plans and construction photos.

Totally amazing.

This is the eighth part of an ongoing series about building a low cost, open source streaming internet radio based on the ASUS WL-520gU Wireless Router.  If you haven’t already, check out the previous parts (see the links at the end of this article) for some background about the project.

In part seven, we added an LCD status display for the radio that shows the stream name as well as the artist and title of the current track.  In this part, we’ll add a tuning knob that lets us change stations without using a computer.

It turns out that this is mostly a software exercise, made simple by taking advantage of the analog to digital converter function of the Atmel ATmega168 AVR that is controlling the LCD display.  The addition of the tuner control turns the display circuit into a very simple user interface.  Turn the knob and the station changes.  The position of the knob determines what station the radio is “tuned” to, and when combined with a calibrated scale it will make it easy to change to any one of the several streaming radio stations stored as presets (favorites?) in the router.

To give you an idea of how this works, here is a demo of the tuner control changing between ten preset stations I have set on the router.  The tuner control is in the upper right hand corner of the breadboard.  As I adjust the control, the music changes and LCD display updates to show the name of each new station.

Is that cool or what?

If you are interested in adding this functionality to the radio, keep reading and I’ll show you how.

Changes to the hardware:

You will need:

• The completed AVR-based LCD display from part seven
• A 1k-10k trimmer or potentiometer, linear taper
• Some hookup wire

Schematic:

Here is an updated schematic of the AVR circuit showing the potentiometer connected to ADC4 (pin 27).

click to enlarge

Firmware:

The AVR firmware has been significantly expanded, slightly reworked and cleaned up in some areas.

The most important changes are:

• The addition of a serial transmit function so the AVR can talk to the router (based on the uart_putchar function)
• New code supporting the analog to digital converter (ADC) which reads the value of a potentiometer connected to ADC4.
• A new Timer1 overflow interrupt has been added, which occurs roughly every 0.5 seconds.  The interrupt service routine (ISR) checks the position of the tuner control, and if it has changed, sends the value to the router.  The ISR is towards the top of the file, see the SIGNAL (TIMER1_OVF_vect) section.

The ADC range of the ATmega is 0 – 1024 for an input voltage from 0 to 5V.  The AVR sends serial data in the format “Tuner: Value” back to the router when the tuner position changes by more than ADC_SENS counts (default is 5).  The AVR waits for an “AVR Start!” command from the router before sending any data, this avoids filling up the serial receive buffer on the router before it’s ready to start processing data.  An important consequence of this is that the AVR must be reset before running the control script on the router.

You can download the source code and compiled .hex file here.  Flash it to the AVR using any compatible ISP programmer and you should be good to go.  The source is commented fairly well so if you’re interested in learning how the interface works, take a look.  You will need a copy of the ATmega168 datasheet to understand the register names and other architecture-specific parts of the code.  Feel free to post in the comments with any questions.

Modifying the circuit:

This part is pretty simple – just wire the potentiometer as shown in the schematic.  Most potentiometers have three terminals.  The left terminal goes to ground, the right one to +5V, and the middle terminal to ADC4 on the AVR (pin 27).

Tweaks to the OpenWrt configuration:

To make bidirectional communication with the AVR work, we have to change a couple config files on the router and disable some services that would otherwise get in the way.

/etc/config/network

The first change is to modify the /etc/config/network file so that we can always telnet or ssh into the router on a LAN port using the IP 192.168.1.1.  The ability to access the router via ethernet is helpful in case we screw something up and lose the wireless connection or the router loses it’s IP address, etc.

Modify the LAN section of /etc/config/network to look like this (changes in bold):

#### LAN configuration
config interface lan
#option type     bridge
option ifname    "eth0.0"
option proto    static
option ipaddr    192.168.1.1
option netmask    255.255.255.0

Save changes, restart the router, and connect an ethernet crossover cable (straight cable might work on some computers) to the router.  Configure your desktop/laptop computer with a static IP, like 192.168.1.185.  Try to open a telnet connection (or ssh if you have set a password on the router) and see if you can log in.  If not, don’t continue with the next steps until you can get this working.

/etc/inittab

We previously used the router’s serial port to get a login shell.  Now that we’re trying to receive data from the AVR on the same serial port, we need to disable the login shell or it will capture the data before we can get to it.

Edit /etc/inittab to look like this (changes in bold):

::sysinit:/etc/init.d/rcS S boot
::shutdown:/etc/init.d/rcS K stop
#tts/0::askfirst:/bin/ash --login
#ttyS0::askfirst:/bin/ash --login
tty1::askfirst:/bin/ash --login

/etc/sysctl.conf

Sysrq is a fascinating and very low level debugging feature of the Linux kernel.  It can be used to perform troubleshooting operations and reboot the system.  Usually it is invoked with a magic key combination on a desktop computer, but in this case I found that it is easy to accidentally trip over the serial port when using an AVR.  (The “break” RS-232 code triggers Sysrq, this probably has something to do with it.)

Fortunately, it’s easy to disable by editing the /etc/sysctl.conf file and adding these lines:

# Disables the magic SysRq key
kernel.sysrq = 0

Reboot the router to apply the changes.  Now we can get on with the good stuff!

Shell scripting magic:

The real action happens on the router, where a shell script waits for input from the router and changes the station accordingly.

This script is called interface.sh and can be downloaded to the router using wget as shown:

root@OpenWrt:~# cd ~
root@OpenWrt:~# wget http://mightyohm.com/files/wifiradio/interface.sh
...
root@OpenWrt:~# chmod ugo+x interface.sh

The interface script calls an updated version of the display script from part 7, called display2.sh:

root@OpenWrt:~# wget http://mightyohm.com/files/wifiradio/display2.sh
...
root@OpenWrt:~# chmod ugo+x display2.sh

Once both scripts are downloaded, executable and located in /root you can launch interface.sh as follows:

root@OpenWrt:~# ./interface.sh
volume: 60%   repeat: on    random: off
volume: 60%   repeat: on    random: off
adding: http://relay3.slayradio.org:8000/
adding: http://scfire-dtc-aa01.stream.aol.com:80/stream/1046
adding: http://208.101.28.234:8004

… more stations here …

Tuner Position:  0
New station...

http://relay3.slayradio.org:8000/

[playing] #1/10   0:00/0:00 (100%)
volume: 60%   repeat: on    random: off

The interface script adds ten presets to the router, shows the playlist, and then waits for valid tuner data from the AVR.  Once it receives a “Tuner: value” line (which should occur shortly after the AVR receives a go signal from the script), the script prints the received tuner positon and changes to the requested station.  It will then wait for new tuner data from the AVR and change the station when necessary.

As you can see in the video, this works very well.  Over a fast Wi-Fi connection, the time to change stations is almost instantaneous – very satisfying!

That’s it for part eight.  In part nine, I’ll add some finishing touches to the router configuration and start talking about enclosures.  Stay tuned!

Update: There is a new Wifi Radio Discussion Forum, hop over there to ask questions about the project or see what other people are working on!  (4/12/09)

Update 2: Part nine is now available.

My friend Tony created an instructable about his Heated Stage for Thermosonic Wedge Bonding, based on my PID controlled soldering hotplate design.

Tony is building a home wirebonding station so he can work with microwave MMICs and build very high frequency amateur radio transceivers.

Nice job, Tony!

Last week I posted about the DIY PID-Controlled Soldering Hotplate I designed and built to improve my surface mount soldering capabilities.

I mentioned one issue I was having with the hotplate on flickr.  Specifically, the aluminum baseplate was getting too hot for comfort (literally) when I set the hotplate to solder reflow temperatures (180-220C) for more than a few minutes.  At the time I thought it was due to radiant heat from the upper aluminum block transferring to the bottom plate.  I later discovered that the ceramic spacers I used to hold up the hotplate were much more thermally conductive than I thought and the screws I used to attach the baseplate to the spacers were burning hot before the rest of the baseplate.  It was conducted heat, not radiant, that was the primary cause of the problem!

McMaster-Carr to the rescue!

I was able to resolve the issue by reducing the diameter of the ceramic spacers from 1/2″ to 1/4″ and using all stainless hardware to attach the spacers.  Now the baseplate stays relatively cool even with the hotplate at high temperatures for long periods of time.

Click on the pictures below or view the complete set on flickr.

In preparation for my Arduino-based AVR HV Programmer boards coming back, I decided to step up my home lab surface mount soldering capabilities.

Step one was to find a cheap stereo zoom microscope on ebay, with 7-32X magnification, perfect for working on surface mount devices.  One of my biggest frustrations in the past is that with a cheap magnifying ring light, I can’t actually see what I’m working on – not any more!  I’ll post some photos of the microscope when it comes.

Step two was to build a soldering hotplate.  I like using a hotplate for surface mount soldering because you can actually watch the board as the solder paste reflows, and manually add/remove/nudge components around with a set of tweezers.  This is great for engineering work where you may still be making component changes and other tweaks to the board.  Mass production is probably best left to a reflow (aka toaster) oven.

I posted a few photos of the hotplate on flickr, which ended up on Hackaday.

The hotplate:

The heater is a 1/2″ 500W, 120VAC cartridge heater I bought from McMaster-Carr for about $25.  The hotplate itself is a 3x4x1″ chunk of aluminum that I machined with a carefully sized hole just below the center for the heater to slip into, as shown.  A type-K thermocouple (top right) measures the temperature and provides a signal to the controller.  Ceramic standoffs insulate the hotplate from the bottom aluminum baseplate.  For safety, there is also a ground strap, shown on the bottom right.

This the second PID controlled project I have done, the first was my PID Controlled Solder Paste Fridge.

The controller:

The controller box contains an Omega CN77000 series PID controller and an IR/Crydom 240V 40A (overkill!) D2440 Solid State Relay (SSR), along with a power switch, fuse, and power connector.  The PID controller and solid state relay were both found at a now-defunct Silicon Valley surplus store for a few bucks each.  A 3′ umbilical cable connects the controller to the hotplate.

60/40 leaded solder reflows at about 185C, and lead-free solder is around 200-230C depending on the alloy.  (Wikipedia has a good list of reflow temperatures.)  The hotplate can easily reach these within a minute or two from room temperature and could get much hotter if necessary.

It can also be used to cure epoxy and perform any other tasks that require a precisely controlled heater – this could be the world’s most overengineered coffee warmer, if not for the dangers of lead poisioning.

Update: I just posted some more information about the microscope.