40 sensors and 9 microcontrollers

[blazespinnaker]

http://www.kickstarter.com/projects/194 ... orite-game

Apparently the 40 sensors are cheap, but I wonder how much installing them, the cabling, and the microcontrollers will cost.

[Krenzo]

Needing 9 microcontrollers makes it sound like it's not very optimized. I wonder if this is just a prototype.

[MSat]

Low-end microcontrollers are cheaper than many MEMS sensors. Generally it's more cost effective and easier to implement a uC in a sensor node due to limited number of I2C addresses available for a given sensor, or the need to control the chip select pin on a sensor using SPI, otherwise you would need additional components (more expensive than a uC) or more conductors in your cabling.

[geekmaster]

The sensors are almost free, because they are capacitive sensors, meaning they are just a piece of metal foil connected to a microprocessor input pin through a resistor. The only reason for needing a bunch of microprocessors would be to get more input pins, although that could also be accomplished by using a single microprocessor and some shift register chips (or another input multiplexing method). Microprocessors are very inexpensive these days, and perhaps easier to obtain in some cases, so not much extra cost to use a bunch of them, especially if that simplifies firmware development for the Virtuix team.

Simple capacitive sensing:
http://playground.arduino.cc/Main/Capac ... n.CapSense
That example shows one input pin per sensor. One common output pin can drive many sensors. Your body forms part of the capacitor when it is near a foil plate, and the software times how long it takes to charge that capacitor to determine how close your foot is to the foil. Simpler software only needs to know if your foot is over the sensor, not how far away it is...

[MSat]

Ah, I figured they were talking about MEMS sensors (I didn't see mention of anything on that page, and I didn't watch the videos). Still, microcontrollers can be cheaper than devices such as I2C IO port expanders, and not significantly more expensive than a typical shift register, while making implementation easier.

[Krenzo]

uControllers may be cheap, but if the Omni takes off that's money wasted times thousands on having 9 uControllers compared to using one with more power/IO ports. I wonder how they're getting all 9 to communicate with the host computer, 9 separate USB connections?

[geekmaster]

uControllers may be cheap, but if the Omni takes off that's money wasted times thousands on having 9 uControllers compared to using one with more power/IO ports. I wonder how they're getting all 9 to communicate with the host computer, 9 separate USB connections?

Perhaps one master controller with USB port, plus 8 slave processors (acting as IO expanders).

[Haloar]

Would it be cheaper still to attach a permanent magnet to the sole of the shoe and when it moves past one of N coils of wire it creates an EMF in proportion to the rate of change of magnetic flux (speed the magnet and therefore your foot is moving).

I can't quite remember the physics but I believe it was Faraday's Law.

[MSat]

Would it be cheaper still to attach a permanent magnet to the sole of the shoe and when it moves past one of N coils of wire it creates an EMF in proportion to the rate of change of magnetic flux (speed the magnet and therefore your foot is moving).

I can't quite remember the physics but I believe it was Faraday's Law.

Possible, but you would need a substantial number of coils.