The XL_STAR schematic dated Monday 21st February 2011 does not contain any details of U7 (the IC that can get really hot).
From the picture in the XL_STAR Users Manual on page 9, U7 and C28 have replaced U2 and L4.
The left is the photo in the manual, on the right is a photo of my XL_STAR with the U7 alternative.
(waiting for the original photo to be restored)
U7 is marked with L048B but the closest device I've found is a National DP8345 but according to its data sheet it does not come in a SOT23-5 package. It'll be interesting to see what it is. (It's obvious that it is a 3.3 voltage regulator to replace the MC34727CFC!)
The MC34727CFC looked the perfect part with 3.3V 600mA power output with an input voltage range of 3.6-5.5V ensuring operation with a LIR/PD2450 battery.The battery wouldn't last too long pumping out the power for 600mA.
Using my process of having to "Learn to crawl before you Walk before you Run", I wrote the proverbial "Hello World" program for embedded processors that does nothing more than turn LEDs on and off. The procedure followed is that described in Section 8 (Is Corporal Klinger still wearing a dress?) of the XL_STAR Users Manual but with different code. My program is devoid of any interrupts and just turns LED on and off.
Having the XL_STAR demo program on hand, all I did was to extract the relevant functions and put them into my program. I took this unusual approach so I could get something up and running without needing to know any specfic details of the Freescale MC9S08MM128 microcontroller.
All armed and ready to go I accidentally blew my XL_STAR up.
I had a lapse of concentration when reconnecting my XL_STAR and connected the USB cable to the wrong USB connector.
There are two USB connectors - the right one and the wrong one (for power).
I only came to notice something was wrong when trying to run my program.
In my frantic search to fix this I discovered a new 1.04 revision of the XL_STAR Users Manual (entitled "Developing code for the element14/Freescale XL_STAR board") nowwhich describes this very issue very first few pages and how to avoid it.
Hoping to recover from disaster, I drilled out the PCB hole near C1, checked for the open circuit and powered it up properly.
My XL_STAR sprang back to life. But how wounded? Only time will tell.
I built and downloaded my program and then crossed my fingers. It worked.
I then also rebuilt and downloaded the XL_STAR demo program. It worked.
As a bonus, all of the crosshair LEDS are installed and also got a coin battery holder.
Thanks very much element14!
The coin battery holder is not installed so I'll have to install it.
This is a good opportunity to use my 10mm soldering iron tip. My set of iron tips ranges from 0.4mm to 10mm. Here are a few pictures of them.
0.4mm, 1.2mm, 10mm tips.
Almost all hobbyists, professionals and even manufacturers have the soldering iron temperatures set far too hot. Many use temperatures of 350 degrees Celsius.
All this accomplishes is to burn the flux to a cinder, reduces the lives of the soldering tips and exposes components and PCBs to unnecessary temperatures.
Montgomery Scott (Scotty) from Star Trek used to say "How many times do I have to tell you. Use the right tool for the right job!"
The hint is to use the right tip for the right job and a correct technique. This allows a lower temperature to be used.
For this job, it is obvious that the 0.4mm tip is far too small and the 10mm tip is perfect for the job.
I use chisel tips as this provides sufficient surface area for the heat transfer.
A bit of testing show that the solder on the XL_STAR melts at about 240 degrees C so with my soldering set to that temperature the holder was soldered.
Some would argue that the large thermal mass of the lithium cell holder will suck away the heat from the joint and so it does.
The soldering iron must be able to deliver enough power on demand to keep the joint the right temperature and you need to ensure that this power is transferred to the joint.
A mostly forgotten item from an electronics workbench is flux paste (Order Code 1850216 or similar).
This is actually an essential item and can be used to greatly improve the heat transfer.
Flux remover is another forgotten but essential item. There are many brands and types available from element14.
There's even a "No Clean Flux" remover too!
If you can't get the joint to heat up enough then a little more temperature more can assist. (For Pb free, 280-290 degrees C is acceptable. Avoid exceeding 315 degrees C!, Lower for 60/40 Sn/Pb.
I used my 150W (Yes 150W!) ERSA iCON 1 soldering iron (Order Code 162358) to solder the battery holder.
This iron monitors tip temperature and adjusts the tip temperature as necessary whether it requires more or less.
This picture is from the online catalogue. Don't use the temperature as indicated on this diagram on your XL_STAR unless you want to risk damaging it!!
Here is a demonstration of heating a large area to 200 degrees C. Similar results would have been obtained if the iron temperature had been set much lower because the thermal mass of the large tip radiates the initial spurt of energy with 150W heater recovering the tip temperature very quickly.
Fast forward to 3m02 for the large area heating test.
Here is a photo of the resulting solder joint. Good electrical contact and good mechanical strength has been made without any burnt flux or PCB damage.