dbvanhorn

Member Since: April 7, 2011

Country: United States

  • Create a capacitor with copper on the inner layers, interdigitated fingers. Use an I/O pin to charge this capacitor through a resistor, sensing the cap charge with another I/O pin. When you hit a high, then discharge till you get a low. Repeat. Count the cycles over a given amount of time, and you get a number. Done right, this will sense a single drop of water on a 4 inch square sensing area, and you can watch the drop evaporate. Moist vs dry soil has a different dielectric constant, so the value of your capacitor changes as the moisture changes. I implemented this on an AVR very easily.

  • It’s not hard to do a moisture sensor using a four layer board, with the sensor copper on layers 2 and 3, such that the sensor never actually contacts the dirt, which eliminates the corrosion issues.

  • Cool!

    I wrote an enigma machine for the AVR back probably 2007 or so. I had just finished a print cartridge system for a client that used multiple wires for communication. I only needed two, but they had designed in eight, so I set up my comms on two lines and fed digital noise down the other lines, and radically changed the comms speed (clocked serial) so as to frustrate a logic analyzer attack, then I started changing which wires I was using to communicate every so often, and finally encrypted the data that was running over the link. I don’t think it ever got hacked. Paid the bills… :)

    The enigma is still a pretty cool little beast. Brute force cracking it is still rather difficult. http://www.bytereef.org/m4_project.html

  • I just bought one today, and having NO luck getting it to connect with my PC. Start gives me “open device failed”. There’s a dropdown for “unit” in the top center, but it is blank.

    No idea what’s going on, but I bought it specifically to put a meter on a projector for classes. Hopefully someone from SF will chime in here, otherwise I will have to get something different.

    SOLVED!! Despite the instructions above, the software which is linked on this page is NOT the software that comes on the little orange CD with the meter. My laptop has no CD drive so I used the download link. BOTH versions of the software on the disk work with my meter. You have to manually try comports, but it does work.

    Otherwise the meter looks fine, but the ONLY reason I bought it isn’t working. :(

  • They have a whole series of these books, this is just one.

    VERY well done, I think it’s a wonderful thing for something like a first year high school course. It gets the points across easily and not too much fluff, but they do make it entertaining. Not a replacement for “Understanding Physics” by Asimov.

  • Aha moments:

    Why a light bulb in a house gets brighter while an appliance elsewhere is on. Why some fixtures burn out lots of light bulbs. Why the proper application of a finger can fix many circuits. (limited use in high voltage applications)

    Flyback diodes: I know “everybody does it that way” but the common diode across coil method protects the switch (or transistor) at the expense of slowing down the relay contact opening and increasing contact wear in many applications. A zener across the switch is a much better implementation, allowing the field to collapse quickly and not over-protecting the switch or transistor. Simply rate the zener a bit below the max voltage of the transistor/switch.

  • You could take a picture with it sitting on a US $0.25 piece. At least anyone worldwide can work it out from that.

  • A very nice unit.

    I decided to get this one after using the stations we have here at work. (different brand) This one is every bit as good. A little large, but for what it does, it would be hard for it to be small. You will definitely want to practice on some scrap boards first, as it is very easy to get it too hot and delaminate your PCB! Once dialled in it is just like magic.

    It sits next to my metcal, and I think it’s every bit as useful. :)

  • The ArduinoTransporter needs a little debugging yet.

  • The usual suspects.

No public wish lists :(