Hackit: The Bronco Table

While attending LA SIGGRAPH Maker Night, we got to talk to [Brett Doar] about his Bronco Table. The table is meant to make life more difficult by bucking off anything that’s set on top of it. Right now, it uses a tiny piezo mic to listen for the impact and then drives three leg motors in a random pattern. He envisions later generations either running away or following you intently when something is set on them.

The main problem with the current design is that you have to hit the table hard enough to make a noise the mic can pick up. The ideal solution would be able to detect anything, no matter what the material or how forcefully it was set down. How would you detect objects being placed on the surface (table doesn’t have to be wood)?

31 thoughts on “Hackit: The Bronco Table

  1. Why not just detect a change in weight? Put a pressure sensor in one of the legs. Anything above the tare weight of the table triggers the action. I think I have seen reference designs for microcontrollers for this idea. The sensor would have to be pretty sturdy if the table is going to be hopping around.

  2. You could trigger with a sheet (or woven matrix) of dual-sided metal-screen-printed PVDF – the slightest touch will create a voltage between each side. You need a very high impedance amplifier to pick up such small signals however.

    Or trigger by one or more light sensors that the placed object obscures.

  3. Use a resistive sensor; you should be able to rig up a simple mechanism that changes resistance based on the mass of the tabletop. That method allows any surface you want.

  4. To detect an item on the table, use a piezo weight sensor as they use on dump trucks to sense load.

    Also, use a ring of thermal sensors around the outside edge of the table which lock onto a signature, and can follow the person who was nearest the table when an item was placed on it.

  5. I’d just rig the tabletop with a digital scale and have a microcontroller watch the readings. If anything brings it a grain above zero and keeps constant, activate.

    I say constant because I wouldn’t want it triggering because of a bump, currents from the AC, or someone resting their arm, but I’d like to see it sensitive enough to rock any static load larger than a quarter.

  6. Well, a sheet of aluminum or stainless or copper would make for a nice tabletop, and then you could wire it up using inductance/capacitance like one of those touch sensitive lights, iPod controls, etc.
    OR, to avoid the then problem of “what if skin doesn’t actually touch the top”, experimenting with embedding an array of cheap small light sensors under a piece of frosted glass…

    I like the simplicity of this nice table with the three legs, for random bucking, great, but how would you all handle the following / running away table bit???

  7. How about a frosted glass or acrylic surface over a camera with a wide angle lens. When something is placed upon the surface the camera will detect an instance of high contrast.

  8. make two round tops, first one is mounted where the current one is, with a hinge and a cheep contact switch, second round top hinges shut directly ontop of the old one and the contact switch. when the load is placed, it changes the switche’s state. the nice thing about it is you can change the load that trips it via placement of the switch, and it’s very simple to connect to the existing system, the controller just has to watch for that pin to be pulled differently by the switch being moved and then react accordingly.

  9. if a 3mm high / 1″ wide border is acceptable on the table, I’d put a wooden ring on the table, and in this ring I’d put some IR (or RGB ;) ) leds and phototransistors. By pulsing the led you can recalibrate the readings when the leds are off so you can adapt to exterior light. By combining readings from the different captors, you can know where on the table is the object.

    I have a plan to make a multi-“touch”pad this way… one day.

  10. Frustrated Total Internal Reflection. No matter what is placed on the table, so long as it is contacting the table you have the ability to “see” it. The best way to do it would be some trial and error. There would be no need to use a camera or anything that high tech as some simple photo resistors might work great. It keeps a clean top, with a small border and if done right will look really cool. Colored LEDs could add even more of an effect.


  11. Just a question,

    With the current mic configuration… would it be possible to trigger the table with a clap, snap, sneeze, or some other loud noise of the same sort?

  12. If you us a camera, you may also be able to fix the following and avoidance bit. You use a wide angle lens up close to a glass topped table and then just follow or avoid largish moving shapes. Black and white is good enough. It wouldn’t be able to avoid obstacles, but would follow or avoid any moving body.

    Avoidance: If it was already in motion and came across a dresser or sofa edge or something, it would see it as a moving body and would then move away. Eventually it would find itself in the middle of the room, away from all furniture.

  13. Make a big capacitor. A big piece of unetched PC board material, or even an aluminum/paper/aluminum sandwich. You could probably hook right to the existing microphone input. You get a nice little current spike from

  14. Just an idea, not sure if it will work. Basically set up a capacitor across the length of the table and detect changes in electrical conditions caused by putting an object in between- basically introducing a dielectric. The problem might come in changes in humidity and the like.
    Or, maybe RF modulators can be used- something like a theremin, using the heterodyne principle. I’m not sure it would work with all materials, though…

  15. Some of the ideas posted are cheap and available. Others are far less utilitarian (e.g. a border of photo cells does NOT a multi-touch display make, especially when multiple contacts are collinear, except at an exceedingly high density and directionality of sensors).

    My suggestion? Hypersonically vibrate the table surface at or near a multiple of its resonant frequency. It could in principle pick up the damping effect of a hair or speck of dust.

  16. @#16, tgbm said:
    With the current mic configuration… would it be possible to trigger the table with a clap, snap, sneeze, or some other loud noise of the same sort?

    This is mainly why I opted for a microphone rather than a pressure sensor- it allows the table to sense beyond just what’s on the table top, and allows it to be a little more unpredictable. You could also fool it if you could noiselessly put something on it. It’s not so much that it wouldn’t let you put anything on it, but that you’d have to meet it on its terms rather than yours. I think the main issue is the surface of the table, and how good of a transmitter of vibration it is. I’m also not amplifying the signal from the piezo, so it would probably benefit from that. Thanks so much for such thoughtful comments, everyone!

  17. Build a bridge out of her! Seriously though just make the table square and use a touch screen monitor for the table top. Would allow for other cool stuff too if ya think about it.

  18. Solder a pin to the center of a piezo buzzer (flat, round) perpendicular to the surface of the copper side. Solder a mic ground lead to the other side of the copper, the signal lead is soldered to the center of the piezo material. Connect the mic lead to an opamp. Poke the pin in the center of the bottom of the table. An opamp based amplifier (very high impedance) will detect even a flee landing on the table top.This setup works for high frequencies (it will act as a giant ear) as well as for low frequencies (it can detect earthquakes.) Multiple sensors, one in each leg, might be needed to reject false positives.

  19. There are a lot of interesting ideas here, but I haven’t seen the one that I thought was obvious: Use an accelerometer chip to detect the deflection of the table when you put something on it. It should easily be sensitive enough. In fact you will probably need your software to filter out small vibrations so that just walking by the table won’t set it off. Just search Digikey for “accelerometer” and you will find hundreds. They’re small and cheap and come in IC packages.

  20. Check this out… it’s a piece of fabric and a piece of antistatic plastic that’re combined and used to detect pressure.

    It can light a LED, maybe it can trip a relay or something and set this table in motion.

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