everhack Stuff I've been messing with, or just thinking about.

26Feb/1211

smd pcb rfid on the Cricut (semi-fail)

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.

Comments (11) Trackbacks (0)
  1. I’d assume the antennae have quite a bit of capacitance, does that affect the output?

    I’m surprised you are able to get such fine traces on the Cricut. Why “extreme speed”? If I wanted control my first impulse would be to put it on “slooow”.

    Our hobbies seem to have diverged. Last night G and I did paper mache boxes – quite a difference from surfacemount electronics!

  2. Probably, your problem is that your design lacks a “central hole” to allow the magnetic flux to go inside the antenna. Try to do a new design removing the half inner part in both faces.

  3. Have you ever tried to program your own cartridge with your own svg’s so its pc free? Id love to be able to have a cartridge i could add custom SVGs on as i see fit.. carry the cricut out into the living room and cut while i watch tv since i have several cuts to make and never have to get off the couch

  4. Hey, cool design, you think it will work for using that as a reader antenna.

    • Im not sure! At the time, I didn’t realize I could adjust the capacitor for various inductance values, so maybe! I really need to get myself an inductance meter (or make one 🙂 and try again..

      • Thanks for replying, cant figure out why there isnt a PCB for this kind of antennas, most commercial come with a PCB antena attached to the reader… 🙁

  5. Do you sell parts for a Cricut Expression model #CREX001? I have one that the “size” board is cracked, and I would like to find one. The machine works perfectly otherwise.

  6. Just wanted to say that if anyone has an issue with their Cricut machine…this website has been the most helpful of all. Thanks again.


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