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"Freeforming" Transistor H-Bridges — Parallax Forums

"Freeforming" Transistor H-Bridges

ercoerco Posts: 20,260
edited 2010-07-26 15:20 in General Discussion
I had never heard the term "freeforming" before, which means soldering components directly, no PC board!

http://www.beam-online.com/Robots/Tutorials/Freeform/H-bridge/hbridge.html

connectionsa.jpg

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·"If you build it, they will come."

Comments

  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-07-22 06:11
    Ah yes very similar to dead bug .

    Peter KG6LSE

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    "Carpe Ducktum" "seize the tape!!"
    peterthethinker.com/tesla/Venom/Venom.html
    Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway. —Tanenbaum, Andrew S.
    LOL

    Post Edited (Peter KG6LSE) : 7/22/2010 6:17:37 AM GMT
  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2010-07-22 07:45
    I like to do dead bug style wiring.
    It's a great way to create a small project with something
    like an ATtiny uC. I epoxy a Tiny88 upside down on the
    circuit board of those 3.00 ebay 2-line LCDs and just wire
    direct to the pins = a less than 5.00 LCD you can control
    any way you want. Plus you can use the extra left over
    processing power and I/O pins of the 88 to assist the projects
    main uC.

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    justasm.blogspot.com/
  • lardomlardom Posts: 1,659
    edited 2010-07-22 15:37
    Interesting. But·no diodes?

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  • localrogerlocalroger Posts: 3,452
    edited 2010-07-22 16:57
    Freeforming is very popular with the BEAM robotics guys because you can make circuitry so small and light -- but don't make a mistake or plan on repairing it either.
  • TinkersALotTinkersALot Posts: 535
    edited 2010-07-22 17:41
    I worked at a repair depot for the DOD for a while some years back and you would be shocked to know how many mission critical things were just built that way. But perhaps it was just the way things were done "back in the day"
  • FranklinFranklin Posts: 4,747
    edited 2010-07-23 04:13
    www.beam-online.com/Robots/Tutorials/Freeform/Bicore/bicore.html
    www.beam-wiki.org/wiki/Freeform_Bicore_Tutorial

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    - Stephen
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2010-07-23 12:01
    Yeah, I have built a few of those and they work quite well with small motors - great for Sumobots. Mainly, the challenge is to get 6 transistors epoxied together; the rest is easy. Also, use the higher output 2n2222 and its compliment. It is rather silly to use the 2n390x.

    BEAM also stacks ICs to double the power output.

    Why limit yourself to following imaginary rules when nobody really is trying to control your creativity. Spend a bit of time making ICs do things that they were never designed for.

    In many cases, a hot glue assemby is quite handy as well. Wires don't come loose, lots of insulation; but you can easily do rework.

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    Ain't gadetry a wonderful thing?

    aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2010-07-23 16:43
    Loopy

    You could stick the 6 transistors down into a block of stiff modeling clay.
    Do your soldering, and then squirt some epoxy or hot glue to
    fix the thing together.

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    justasm.blogspot.com/
  • soshimososhimo Posts: 215
    edited 2010-07-23 17:49
    Are the two extra transistors used for the flyback protection diodes then?
  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2010-07-23 18:12
    From the image I don't think it has any protection of any kind.
    This is ok as long as you never send a high signal to both 3 and 5
    at once.....the thing would start to smoke if you did!?

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    justasm.blogspot.com/
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-07-23 18:31
    Freeforming is very popular with the analog and RF crowds. Radio hams call it "Manhattan style" prototyping, since it's built like skyscrapers upon a base made from copper-clad. In circuits like these, short, direct connections count more than tidiness if they can reduce noise pickup, crosstalk, or stray feedback and its attendant oscillations. I've seen photos in EDN of some of Bob Pease's (National Semiconductor analog guru) rats-nest creations. You wonder how they could possibly work, but they do.

    -Phil
  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2010-07-23 18:37
    PhiPi

    If I did something really involved I would build
    it in stages and after testing each stage I would
    finalize that stage by covering it with hot glue smile.gif

    We should have a contest to see who could make
    a working uC project of some complexity using this
    style of wiring....prize to go to the one with the most
    outrageously haywire look.

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    justasm.blogspot.com/
  • soshimososhimo Posts: 215
    edited 2010-07-23 20:33
    HollyMinkowski said...
    From the image I don't think it has any protection of any kind.
    This is ok as long as you never send a high signal to both 3 and 5
    at once.....the thing would start to smoke if you did!?

    Hmm, I'm thinking of the flyback protection, not protection from intentionally short circuiting your battery (or PS) which is what would happen if you applied +Vcc to one the top half of the bridge, and ground to the bottom half.

    From other hbridge circuits I've seen there is normally a diode in parallel with the motor and each transistor of the hbridge. So, there should be 4 diodes for flyback protection from the motor. The reason I ask is that I recall in my Advanced Avionics class in the Navy they told us that a transistor can be thought of as two diodes either anode to anode or cathode to cathode (depending on npn or pnp) with the base wire connection between them. Emitter and collection come from the the other side - so base is connection to both diodes and emitter / collector is connected to only one diode. I just had a discussion with a co-worker regarding this. He doesn't believe me. It's been 20 years since I took BEE so please forgive my ignorance but I have to settle this bet smilewinkgrin.gif
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2010-07-24 15:27
    Fly-back protection would likely be two back to back zener diodes across the DC motor's terminals. I am not exactly sure what watt rating as that is dependent on the motor.
    The zeners would have to be rated higher than the operating voltage of motor so that the only conduct spikes. Maxium has similar ready-made devices for protection of circuits that connect to long wires where transients may creep in an kill a valuable board.

    Unlike relays, where a simple diode with serve as flyback protection, you are reversing polarity to reverse motor direction. So a more complex approach needs to be used.

    In reality, these devices are for such small motors that I suspect that flyback protection is a bit of overkill.

    I really wish I could do more of this kind of work, but at 63 years of age, I tend to shake too much for a lot of fine handy work.

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    Ain't gadetry a wonderful thing?

    aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

    Post Edited (Loopy Byteloose) : 7/24/2010 3:34:58 PM GMT
  • ZootZoot Posts: 2,227
    edited 2010-07-24 18:48
    BEAM robots that use small motors generally do not use any flyback diode protection, esp. when freeforming circuits. All of Mark Tilden's published H-bridge, H-bridge w/safety and Bicore BEAM circuits do not use any flyback protection. Techinically, I suppose, you *should*, but in practice, I've never had a transistor on my small bridges fry.

    See, for example, circuits in JunkBots, Bugbots, and Bots on Wheels: Building Simple Robots With BEAM Technology by David Hrynkiw and Mark Tilden.

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    When the going gets weird, the weird turn pro. -- HST

    create bitmap data tool: 1uffakind.com/robots/povBitMapBuilder.php
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  • localrogerlocalroger Posts: 3,452
    edited 2010-07-24 20:48
    Anybody who finds the BS or Propeller of interest absolutely should have a copy of that book Zoot mentions. My wife got it for me as a Christmas present and even though I've never built a BEAM robot (at 46, I'm starting to see a little of the blurry vision shaky hands problem Loopy mentions, plus I've just got too much other stuff to do) but I ate up the ideas; it really is a whole different way of looking at things, and a lot of what I do at work could be considered "robotics" if you squint a little and look at it sideways.

    At Amazon: http://www.amazon.com/JunkBots-Bugbots-Bots-Wheels-Technology/dp/0072226013
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2010-07-25 07:22
    The BEAM websites used to have a whole series of improved H-bridge circuits as well as 'the basic one' that is shown here. There were months and months of evolution and discussion about fitting the right size transistors and resistors to make it work better. Why so? Well when you are using solar power, you just don't have much that you can waste. That is also the case with small batteries. Of course, the same rationale means that unneeded parts are not included. So the flyback diode is really extra weight. It gets down to using 1/8 watt resistors instead of 1/4 watt ones.

    I do have the Junkbots book. My only disappointment is that it is getting harder and harder to find good junk. The items mentioned in the book are not so easy to locate anymore.

    But I do have a couple of tiny, tiny stepper motors salvaged from 3 1/2" disk drives that can be easily driven directly from a BasicStamp that I ponder about. If I used an SXchip in SMD format (I do have some), I might get the size down to power a little solar robot with a lot of digital control, maybe a line follower.

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    Ain't gadetry a wonderful thing?

    aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
  • Martin_HMartin_H Posts: 4,051
    edited 2010-07-25 12:46
    A few months back·I was buying parts from Solarbotics and ordered a copy of that book to boost the total over $75.· It turns out that one of the authors of that owns or works at Solarbotics because he sent·me a signed copy.··The book is a fun read and shows a really different take on robot building.

    I've recently seen a·freeformed microcontroller and support circuitry too:

    http://www.geocities.jp/arduino_diecimila/obaka/project-2/index_en.html
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2010-07-26 15:20
    Now that I think of it, I could probably freeform a Propellor 40pin dip if I glue the EEPROM upside down as a dead bug + crystal + reset + led, and maybe a voltage regulator.

    This looks like a lot of fun. And it could be quite handy as well.

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    Ain't gadetry a wonderful thing?

    aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

    Post Edited (Loopy Byteloose) : 7/26/2010 3:34:16 PM GMT
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