Scratch

THE UNOFFICIAL SENSOR BOARD FAQ


====General Questions===================================================

1. What is a sensor board?

The PicoBoard (formerly the Scratch Board) is a board that you plug into one of your computer's USB ports so that your Scratch programs can interact with the outside world. The terms "sensor board," "PicoBoard," and "Scratch Board" mean the same thing. For an overview, see: http://www.picocricket.com/picoboard.html

2. What comes with the sensor board?

It comes with a Serial/USB interface cable and four sets of alligator clips. It also comes with a cardboard box you can use for arts and crafts or to house a hermit crab -- temporarily.

3. What sort of sensors does it have on it?

A button, a light sensor, a slider, a sound sensor, and four resistance sensors.

4. Does it have any outputs (so, like, I can control a robot arm or my MindStorms?)

Not really. Your Scratch program is the output (which has sounds, graphics, etc.). But there are ways to communicate with external devices. See: http://scratch.mit.edu/forums/viewtopic.php?id=9458

5. How do I set it up, and where do I get the drivers?

http://www.picocricket.com/picoboardsetup.html

6. How do I start playing with it?

http://www.picocricket.com/pdfs/Getting_Started_With_PicoBoards.pdf

7. Where can I get the technical specification?

http://scratch.mit.edu/files/scratchboard/ScratchBoard_Tech_InfoR1.pdf

8. What's the difference between the old Scratch Boards and the new PicoBoards?

From andresmh: "The Playful Invention Company (PICO) is now selling the Scratch Board under the name PicoBoard. The PicoBoard is exactly the same as the ScratchBoard, they just have a different name."

9. How much does the PicoBoard cost?

About $50 (U.S.). Check the PicoCricket site below for details.

10. How do I order a PicoBoard?

Through the PicoCricket site: http://www.picocricket.com/order-picoboard.php

11. Why is the PicoBoard more expensive than the old Scratch Board?

From millner: "The Scratch Board was subsidized by the Lifelong Kindergarten group at MIT, and thus it could be sold at a lower price. Unfortunately, that approach was not sustainable for the long term. The MIT Scratch Team decided it was better to rely on outside groups (such as PICO) for production and distribution of sensor boards that work with Scratch."

12. Is there a way to see how it works without buying one?

Funny you should ask: there is a PicoBoard simulator at:
http://scratch.mit.edu/projects/chalkmarrow/188919

13. Is there a gallery or something where I could see some example projects?

There are not a lot of projects online, but you can find some at:
http://scratch.mit.edu/galleries/view/21836

14. Will sensor board projects work online?

The sensor blocks will not work online. You have to download the Scratch project to use it with the sensor board.

==== Beware! Really Nerdy Questions Below This Line! Stuff you don't need to know to enjoy your PicoBoard ======================

15. I'm a budding EE. Can you show me the schematic?
Sure. Try:
http://scratch.mit.edu/files/scratchboard/ScratchBoardSchematicR1.pdf

16. What components were used for the board?
It may vary, but this will give you some idea:
http://scratch.mit.edu/files/scratchboard/ScratchBoardBOM.pdf

17. How do the sensors convert their input to values between 0-100?

From the Technical Info document:
"Scratch maps the 10-bit sensor data onto a 0 – 100 scale using a mapping that is different for each sensor type. Users can access the “raw  10-bit values by shift-clicking on the Scratch Board Watcher and selecting “report raw data . Doing so will show sensor values in the range 0 - 1023. Most of the sensors use a generic linear conversion to report scaled values between 0 - 100. Light and sound sensors use piecewise linear functions that take into account the idiosyncrasies of those sensors. (Note that readings for light are reversed so that more light gives larger values.) Code for scaling functions [are]:

generic(n)
   return round ((100 * n) / 1023)
light(n)
  if n < 25 return 100 - n
  else return round((1023 - n) * (75 / 998))
sound(n)
  //empirically tested noise sensor floor
  n = max(0, n - 18)
  if (n < 50) return n / 2
//noise ceiling
  return 25 + min(75, round((n - 50) * (75 / 580)) )
//noise floor and ceiling values might vary

18. Um. OK. But in reality, how do the resistance values relate to the sensor value? Is it linear?

Nope. It's not linear. It's logarithmic. From experiments on our board, the resistance sensor value (0-100) that the PicoBoard produces is related to the actual resistance, R, (in KOhms) across the alligator clips by the something like the following equation:

sensor value = a*ln(b*R+1) where, approximately:

a=19.5
b=0.9

BUT, if you are only interested in low resistance values between 0-10 KOhm, the following simple relation works real well (and yep, it's linear):

sensor value = a*x, where a is approximately 5.57

19. What microcontroller does the sensor board use?
The bill of materials lists a MicroChip "PIC" device: PIC16F676, which, if you're so inclined, you can read about at:
http://ww1.microchip.com/downloads/en/DeviceDoc/40039E.pdf

20. Why is it called a "PicoBoard"? Is it 1x10^-12 of a board?

lolz. no. It's an acronym for "Playful Invention Co."

Last edited by chalkmarrow (2009-01-26 15:30:56)