Using the "industrial" sharpies, fine and ultrafine point, I made two attempts at an AVR RFID card with integrated PCB antenna, with mixed results.
I designed all but the antenna in Eagle and exported to EPS, then imported into Make-the-Cut. The spiral antenna I created using Inkscape spiral tool, then cut-and-paste into Make-the-cut, and just rotate and move so the traces connect.
I draw a rectangular bounding box around the circuit and put into a separate layer, which I print first onto a piece of paper taped on the cutting mat. This shows me exactly where to place the blank circuit board.
Next I tape the circuit board to the paper using masking tape at the very edges only. I snipped off one of the grey friction rollers so it doesn't roll back and forth over the design and ruin it while the ink is still wet.
I remove the Expression keyboard to make room for the pen, and wrap a long thin strip of duct tape around the pen close to the tip to make it big enough for the tool holder to grip. I "cut" (draw) from Make-the-Cut at Extreme speed, low pressure, and etch in the usual way.
The experiment was very successful in that I was able to get pretty reliable traces in two sizes, roughly 0.5 and 0.8 mm, plenty for a sporting shot at surface mount stuff.
Unfortunately, while a magnet-wire coil produces upwards of 10v peak-to-peak, I can't seem to get better than 850mV or so across the pcb coil leads, regardless of my choice of tuning capacitor, so for now running the Tiny85 is still out of the question.
The two antennas have about 25 and 45 turns respectively, but so far I've been totally unable to get them tuned to produce enough voltage to run the AVR.
I've been probing the tag coil across the capacitor leads while the tag is being stimulated at 125khz with my homemade reader.
The second antenna is pushing the resolution limits in the spiral because the "jaggies" from the machine reduce clearance between lines. I had to do a little cleanup work with a razor blade, separating adjacent lines that had shorted in a very few places.
Cricut Repair Info
One way to get yourself a cheap Cricut machine is to buy a busted one off eBay. Try searching for both "broken cricut" and "defective cricut". Often you can win one for as low as $0.99 plus shipping for a Personal or Create model, or somewhat more for an Expression.
Where to get one
The main dealer of these machines, "websbestdeals," must have some exclusive arrangement with PC, because they seem to have a pretty inexhaustible supply of broken machines to sell.
Have patience and don't get carried away with your bid, it seems there will always be more listed within a few days.
Read the seller's description carefully to see what is included. Usually (but not always), they only include the power supply, but sometimes it comes with everything, cutting mat, blade holder, power adapter, cartridge, overlay and even the manual and warranty card. Once in a while they'll sell two for one, but missing one or both power adapters.
Sometimes the seller's description will tell you exactly the issue, as in the case with a dragging blade. I'm not quite sure yet what it means when "the blade makes a lot of noise", but the broken limit-switch wires definitely cause a horrible noise on startup. Many times they simply say "it has no power," which so far often (but not always) indicates a power supply or broken trace problem.
Mine didn't come with a cartridge!
If you don't have a real cartridge, you can make yourself a "Fake George" to at least get a machine with the stock firmware to start up fully. More details here. Basically, you just need to (carefully!) make something that will short together pins 4, 6, and 10 (or 11, 15, and 17) on the cartridge port, to fool the machine into using its own built-in "George and Basic Shapes" cartridge.
Here are some close-up photos of what a real "George" looks like inside.
Removing the Side Covers
Don't rush to take the sides off the machine. Many times this won't be necessary, and it's hard to get the trim pieces off without doing at least cosmetic damage.
The way I do it is to use a thin bladed putty knife to get in between the trim and side cover (from the outside edge inwards), while pulling outwards with your other hand, to depress the little fingers that clip the trim piece on, one at a time. I've broken off quite a few of them with poor technique, but don't usually bother putting them back on anyways.
Once the trim piece is off you can get access to the 5 or 6 phillips-head screws holding the actual side cover on.
Accessing the Motherboard
Usually all the action happens in the bottom of the machine where the motherboard is located.
To access it, all you need is a long #1 phillips-head screwdriver. Roll the machine onto its back on a towel or something else soft, and remove the 8-or-so most obvious screws around the outside of the bottom cover. Then, tip the cover down and towards yourself like opening a panel. If you carefully tug a little on the wires leading up into the side covers you can get just enough slack to be able to rest it flat on the table while the machine is still on its back.
Problems and Solutions
Here are some of the things I have discovered so far while fixing a bunch of these machines:
I don't have a schematic drawn up for these, but one of my Creates is an older model with only a 2-layer board. This makes the circuit far easier to figure out than the 3-layer boards that came later. The Expression board is nearly identical, so this should be of assistance for figuring out those issues as well.
It seems the dials are pretty easy to break if the machine falls onto its front side. The size dial is expendable if you use Make-the-Cut or other cutting software on your PC, but if you cut with cartridges or the pressure dial is broken you may not have much choice but to try and find a replacement dial.
Bad Power Supply
An Expression I got with a bad power supply would constantly turn on and off, like a turn signal on a car. On, off, on, off. Replacing the power brick with a known-good one from another machine solved the problem.
Broken Inner-layer PCB traces
So far, two Create machines have been suffering from broken traces in the middle layer of the circuit board. Fixing these can be challenging since you can't see the inner layer to know where it was supposed to connect to.
Fortunately, I have a working older revision of both Personal and Create motherboards that are only 2-layers, and there were virtually no changes to the parts connections or positions when PC switched to the 3-layer boards. This means you can visually trace the connections on the older board, and verify those connections on the newer (broken 3-layer) one.
I will be adding specifics here to help with this process for anyone who doesn't have the benefit of a 2-layer board for reference.
1) One machine's power button would light up when you turned it on, but nothing else would happen. This was isolated to two broken inner-layer traces leading from the 5V regulator to two nearby parts.
At long last, I took a photo of the repairs for the "broken inner-layer traces" issue.
First photo shows the front of the board. The broken traces connect one of the inductor leads (circled) to the 5v voltage regulator and to the large capacitor below it.
This next photo shows where the jumpers were placed. Your mileage may vary, but this got mine working.
2) Another Create model would power up and boot fully, but the display would be either blank or show only a single line of pixels. Swapping out the display for another known-good one did not have any effect. This turned out to be a broken +5V power supply line to the OLED display connector. (pin 2, counting from the end with the red stripe). I repaired this one by adding a jumper over to the +5V power supply line on the keyboard connector an inch away.
One expression, when you pushed the power button, would light up, but instead of booting would just beep three times and halt. This turned out to be simply a disconnected keyboard cable. The fix was simply to plug the cable back in to the motherboard.
Broken Limit Switch wires
Two different machines had this problem - they would start up okay, but when the carriage would slide all the way to right, it would crash at the end and make a horrible grinding noise. This indicates a problem with the button located in the right-side hidey-hole or the wires leading to it.
Upon removing the right-side cover, I discovered in one case that the pair of wires from the limit switch had been severed by the sharp edge of the metal motor bracket inside. Repairing the wires solved the problem. In another case, one of the wires had simply fallen off the switch, and I was able to just plug it back in.
Broken Solenoid wire
One Create would operate normally, except the cutting blade would not go up and down at all. Removing the carriage cover revealed the problem to be a broken solder joint at the top of the cutter solenoid. Space is pretty tight, but I was able to solder a short length of wire between the broken lead and the stub on the solenoid to fix this problem.
This problem seems to be one of the most common, and the easiest to fix as well. The machine seems to operate normally, except that the blade drags in some places, cutting where it shouldn't, and hangs up in some places, not cutting where it should. Normally, the blade holder should move smoothly up and down. You should be able to push it down with no friction detected, and when released, it should move smoothly and freely back upwards.
In some cases, the lower of the two leaf springs in the cutter solenoid mechanism can get bent, causing a slight misalignment, which creates friction that causes the observed "dragging" behavior.
The fix for this is about the simplest of all: remove 3 screws covering the cutter carriage, and simply pinch with your fingers the upper and lower leaf springs together at the right hinge point. (Where the red circles are in the photo below). This should straighten the bent lower leaf spring and free up the movement.
The power brick is an 18v 2.5A switching power supply with a pretty standard cord end, so you could probably find something compatible, but you can get the real thing from PC itself for $9.99.
I'm not 100% certain, but the US Cutter Refine carriage looks identical from the photo.
I have several machines that I have not yet repaired.
One is a Personal model that will often fail to boot, and show only dark squares on the LCD screen. It was described this way to me before I got it, worked fine upon receipt, but then stopped working again soon after.
Another is an Expression that, when powered on, the power light comes on, but nothing else, and the 5V regulator starts to get very hot. Although replacing the regulator may be the solution, I want to be sure the problem wasn't caused by something else.
(two other Personals have not been checked out yet).
I finally got a few more hours to spend on getting Freecut 0.2 running on the Cricut Create this weekend, and finally got the motors and cutter solenoid up and running. The only remaining things I haven't tried are the dials and flash (I don't have any need for them yet).
I've delayed checking in my changes because I haven't got a Personal model hacked yet to make sure everything still works on it. I'm expecting another one in the mail this week so I'm hoping I'll be able to get to this in the next week or two.
In the meantime, I'm also pressing forward with working to implement HPGL and/or DMPL cutting protocol in place of the existing made-up one that Freecut 0.1 uses. Unfortunately my C-string-programming skills are pretty rusty so it might be a little challenging.
I spent a few hours reading about 125k antenna formulas and designs to try and better understand the relationship between desired frequency, loops of wire, wire gauge, and the value of the tuning capacitor.
I worked through some of the formulas in this datasheet, plugging in 100 turns, 66mm, 30 gauge to see what it would come up with for inductance, ideal # of turns, and capacitor value, to see if they would match the 1nf & 100 turn values specified in scanlime's blog entry. I wrote a simple java program to calculate the values for me after not finding what I thought I was looking for on various online antenna calculators (they seemed to be all too complicated).
I found this interesting note along the way which I had not seen elsewhere: "... For copper wire, the loss is approximated by the DC resistance of the coil, if the wire radius is greater than cm. At 125 kHz, the critical radius is 0.019 cm. This is equivalent to #26 gauge wire. Therefore, for minimal loss, wire gauge numbers of greater than #26 should be avoided if coil Q is to be maximized....".
So, #26 gauge wire next time!
Unfortunately my program isn't putting out believeable numbers yet, so I have more work to do.
In the meantime, I also discovered this other datasheet for a neat little 0.32 cent RFID chip (the Philips Hi Tag-S) that has a good description of the details of the encoding methods used starting in Section 7.3 (including our manchester, for future reference)
And here's another good discussion of the antenna design and coupling (different frequencies, same concepts and formulas).
I played with the open source 4NEC2 Antenna Modeler & Analyzer for a while trying the helical generator, but it kept blowing up at simulation time with my RFID design, complaining that the antenna was connected to ground at the end (duh, this is what the tutorial shows, I don't get it!).
Woo woo, I'm now 6 for 6 on repairing the "broken" Cricuts I got off eBay. (ok, Danny M. gets 95% of the credit for the one with the busted middle-layer board traces)
The last holdout was a Personal model, which would beep three times when powered up. Nothing from the LCD, all the keyboard lights would come on.
I started by plugging a known-good power supply into it, just in case, but it didn't make any difference.
Next, I removed the bottom cover where the motherboard lives, and immediately spotted the culprit. The LCD header was unplugged.
After plugging it back in and powering it back up, angels sang, it started right up and gave me the "Cricut 1.0 OK"!
Incidentally, I had been wondering if the earliest firmware versions had perhaps not been read-only, so I plugged in my handy programmer card and attempted to download the firmware.
At first I thought I had hit paydirt, the file was NOT all 0s like the others, but alas, I realized the bytes were all sequential numbers in an interesting pattern (high-byte increasing across, low byte increasing downwards).
This machine looks pretty much unused and gleaming. I wonder if it was bad right from the factory? How else could a header just come unplugged like that?
One thing that always bugged me about using pens in my Expression is the super short limit on pen length. I love the Staples mini gel pens, and I've gotten pretty good at shortening others, but some (like Sharpie paint pens) just not feasible to do this with.
One video on YouTube shows someone with a Personal model who removed the keyboard which allows a full length pen to be used. Unfortunately, this requires removing the end caps which is kind of a hassle. The Create is even worse, the body of the case extends underneath the keyboard and completely eliminates the option altogether.
Anyhow, with the help of a friend at the hackerspace the other night, I finally figured out how to do this EASILY on the Expression.
Here's photos showing how:
Using the head of the special tool, slide the latch towards the rear of the machine. It's pretty stiff, but don't worry about breaking anything. You could also use a flathead screwdriver for more leverage.
Once the latch clicks, lift up on the left side of the keyboard. The right side is just held down by some plastic fingers in holes in the case and will release when you move the keyboard a little to the left.
Taking care not to tug too hard on the wires, you can now lift the keyboard up and out of the way, eliminating any length limit on pens. On mine, the power wires on the right side were especially short. Taking the right side endcap off allowed me to release a bit more wire, but it doesn't really take much.
Reversing the process is pretty easy, just tuck the right side back in the holes, press the left side down flush, and use your special tool in reverse, this time to pull the latch back towards the front of the machine until it clicks.
As part of learning about HPGL and DMPL plotter protocols recently, I wanted to see some actual samples of code sent to various types machines by any cutting application like MTC or SignCut.
Here's how I did it (in windows):
1) Download and install Eltima Software RS232 Logger and Virtual Serial Port Driver. Unfortunately, although the logger is free software, the VSPD is only a 14 day trial version. You probably can get all the samples you need in just a day or two
2) Using the Virtual Serial Port Driver, create a new pair of virtual serial ports, we'll call them COM1 and COM2.
3) Start the RS232 Data Logger, select COM2, set the baud rate the same as your cutting software will use, and set flow control to None. Select your output file name and click Start logging.
4) Go into your cutting software (MTC, SignCut, etc), configure the cutter type you are interested in (Black Cat, US Cutter, etc...), and set the port to COM1. Make the cut. The software should finish very quickly.
5) Stop the data logger to make sure the file content is flushed, and you are done!
Here is a sample of DMPL code for a test file sent by MTC.
;:H A L0 ECN U U8158,9620;D8167,9620;D8167,9630;D8150,9630;[...];D8463,7116;U0,0;!PG;
While further developing my printed-circuit-board method, I inadvertently figured out how to do filled shapes with the pen using the free version of "Eagle" PCB design software.
1) You'll need to have Eagle (free version is fine), Inkscape, and Make-the-Cut all installed and available. I use Gimp for editing and converting file formats.
2) Open the desired image in Gimp (or other image editor) and save it out as a BMP format image, with as few colors as possible. A 1-bit monochrome with no dithering is best, like line art. (you set this via Image->Mode->Indexed... in Gimp)
3) Start up Eagle, and do a New->Board.
4) Do File->Run, and run the script "import-bmp.ulp". This will be located in the ulp subfolder of your Eagle installation directory. It will prompt you to browse to your BMP file and open it. Keep your bitmap size modest, 300 DPI or less, more just slows everything down. If you have a black-on-white drawing, select White only and click OK. Click the DPI radio button under Format, and set your DPI value; it will set the Scale factor for you automatically. Click OK.
5. It will think and popup window saying "Accept Script?", click "Run script".
6. Your bitmap should now appear in blue in the Eagle Board window. Save your project, then Run File->CAM Processor.
7. Select Output Device HPGL. Deselect all layers except #200 "200bmp". You'll have to scroll down to find it. Click "File" and browse to your desired output file location and name. Be sure to give the file a ".plt" extension which indicates the HPGL file type. Set the Pen Diameter to the actual width of the line your pen produces. 1 mil = 1/1000 inch. A ballpoint pen tip ranges from about 20-50 mils. Click "Process Job". This will render your .plt file.
8. Start up Inkscape, do File->Import... and import your .plt file. This can take a little time. If the application freezes, give it some time.
9. Eventually, your image will appear in Inkscape, already selected. Click "Edit->Copy".
10. Switch to Make-the-Cut, now do "Paste-in-Place". Voila!
Note, depending on how large the filled areas are, and the diameter of the pen, it might take quite a while to calculate when you click the "Cut Project With..." button. (the example image has 65000 points). Fortunately, since the fills are done using mostly horizontal and vertical lines, the machine can run pretty fast.
Here are another couple screenshots to show the pattern closeup. If you wanted a grid you would tell Eagle that the pen is wider than actual.
This method should work really well with engraving tips..
MTC reported this image was about 11000 cutting points which really seems pretty modest to me. I haven't tried actually printing one this big yet. If you (in MTC), right click on the imported image, and do Shape Magic->Advanced->View Path Detail... and scroll down through the path segments with the cursor key, you'll see the path taken is pretty sensible and doesn't waste a lot of time scrolling wildly all over the place.
I created a circuit in Eagle to test the resolution and fills using a fine tip pen in the Cricut.
The pen itself is a 0.01 inch diameter permanent marker, shortened to fit the machine. The test image is made of three identical copies of a diagram. The diagram contains some sample SMD and through-hole pads, as well as traces in 0.01, 0.03, 0.05, and 0.07 inch widths.
The legend reads "10mil pen, 20mil pen" and "30 mil pen" to indicate the pen size as given to the Eagle CAM processor function, but the entire drawing is rendered using the 10 mil pen in order to see which circuit will have proper fills with no white lines inside.
The results prove to me that the best fills do indeed result when the pen size is accurately set in the Eagle CAM processor. When the pen in smaller than Eagle thinks, it doesn't lay down enough lines to completely fill the solid traces. The TQFP and SMD resistor pads look nearly usable, even the horizontal jitter is almost nonexistent near the middle of the page. (Maybe the duct tape pen mount absorbs vibration better than my custom metal pen holder?) The worst flaw just seems to be incomplete coverage in the diagonals of the largest (0.07 inch) traces, which should be easily retouchable by hand.
Here's the workflow:
1) Create the board in Eagle
2) Run the CAM processor, select output device HPGL, layers Vias, Pads, Top or Bottom, and Holes.
3) Start a new drawing in Inkscape. Import the HPGL file into Inkscape. Select the imported circuit diagram, and click "Copy".
4) Mount the pen in the Cricut tool holder.
5) Start Make-the-Cut, and do "Paste in Place" (ctrl-shift-V) to paste without resizing. Arrange as needed and then cut to the machine.