Measure/Blog: Difference between revisions

From OLPC
Jump to navigation Jump to search
No edit summary
Line 4: Line 4:
Some of my ideas, thoughts, back-of-an-envelope sketches and musings regarding hardware interfaces to Measure:
Some of my ideas, thoughts, back-of-an-envelope sketches and musings regarding hardware interfaces to Measure:


[[Image:DiffAmpInterface.PNG|thumb|400px|[[Media:PDiffAmpInterface.PNG|actual size]]|center|A redrawn schematic of the differential amplifier interface as shown on [[Measure/Projects]]]]
[[Image:DiffAmpInterface.PNG|thumb|400px|[[Media:PDiffAmpInterface.PNG|actual size]]|center|A redrawn schematic of the differential amplifier interface as shown on [[Measure/Projects]] - it should be a bit clearer and easier to follow its electronic operation.]]


I've added a fuse and 5.1V Zener diode on the XO input, as you can see - this should, hopefully, be suitable for making these types of electronic interfaces for Measure robust and "noobie-proof".
I've added a fuse and 5.1V Zener diode on the XO input, as you can see - this should, hopefully, be suitable for making these types of electronic interfaces for Measure robust and "noobie-proof".
Line 18: Line 18:
== Project ideas ==
== Project ideas ==


Measuring daily changes in solar irradiance:
=== Measuring daily changes in solar irradiance: ===


Use a suitable interface, such as this, to measure the DC voltage from a photovoltaic module, and log how it changes over a period of a day - I'm sure we could even use the OLPC photovoltaic charging module for this - it has a 12V DC output - just make sure your amplifier/buffer interface will be suitable for that!
Use a suitable interface, such as this, to measure the DC voltage from a photovoltaic module, and log how it changes over a period of a day - I'm sure we could even use the OLPC photovoltaic charging module for this - it has a 12V DC output - just make sure your amplifier/buffer interface will be suitable for that!


Optical barrier alarm:
=== Optical barrier alarm: ===


Turn on the voltage bias, and connect a LDR. Say our LDR has 500k dark resistance and max 2800 ohms in light. (That was measured from a mystery one in my junk box.) Given 785 mV bias with 790 ohms effective impedence, we have then, 784 mV dark input voltage, and 612 mV light input voltage - quite detectable discrete levels.
Turn on the voltage bias, and connect a LDR. Say our LDR has 500k dark resistance and max 2800 ohms in light. (That was measured from a mystery one in my junk box.) Given 785 mV bias with 790 ohms effective impedence, we have then, 784 mV dark input voltage, and 612 mV light input voltage - quite detectable discrete levels.
Line 28: Line 28:
1 mW 660nm red laser diode modules are cheap and easily accessible for experimenters - but remember, if working with children or young people, teaching prudent laser safety is a good idea, even at this power level.
1 mW 660nm red laser diode modules are cheap and easily accessible for experimenters - but remember, if working with children or young people, teaching prudent laser safety is a good idea, even at this power level.


Temperature acquisition:
=== Temperature acquisition: ===


Using the simple LM335 probe, described in detail at [[Measure]], a simple classroom demonstration of Newton's Law of Cooling can be realised, using the computer as a datalogger.
Using the simple LM335 probe, described in detail at [[Measure]], a simple classroom demonstration of Newton's Law of Cooling can be realised, using the computer as a datalogger.

Revision as of 15:58, 29 January 2008

Share your experiences with Measure Activity here!

(be sure to include as many pictures as you can)

Some of my ideas, thoughts, back-of-an-envelope sketches and musings regarding hardware interfaces to Measure:

A redrawn schematic of the differential amplifier interface as shown on Measure/Projects - it should be a bit clearer and easier to follow its electronic operation.

I've added a fuse and 5.1V Zener diode on the XO input, as you can see - this should, hopefully, be suitable for making these types of electronic interfaces for Measure robust and "noobie-proof".

This is all my half-baked, untested, back-of-an-envelope stuff - no promises it works! Peer review, comments, feedback, or criticisms are all welcome.

I don't claim all these ideas as unique or new - but I'm trying to take existing project ideas from the projects page and flesh them out a little more.

I don't have access to an XO-1 machine - if any developers who do might like to test my ideas, as they mature, I'd love to hear the results!

An example PCB layout for same. I'm sure someone might like to improve on my PCB design skills, or re-draw it using FOSS EDA tools.

Project ideas

Measuring daily changes in solar irradiance:

Use a suitable interface, such as this, to measure the DC voltage from a photovoltaic module, and log how it changes over a period of a day - I'm sure we could even use the OLPC photovoltaic charging module for this - it has a 12V DC output - just make sure your amplifier/buffer interface will be suitable for that!

Optical barrier alarm:

Turn on the voltage bias, and connect a LDR. Say our LDR has 500k dark resistance and max 2800 ohms in light. (That was measured from a mystery one in my junk box.) Given 785 mV bias with 790 ohms effective impedence, we have then, 784 mV dark input voltage, and 612 mV light input voltage - quite detectable discrete levels.

1 mW 660nm red laser diode modules are cheap and easily accessible for experimenters - but remember, if working with children or young people, teaching prudent laser safety is a good idea, even at this power level.

Temperature acquisition:

Using the simple LM335 probe, described in detail at Measure, a simple classroom demonstration of Newton's Law of Cooling can be realised, using the computer as a datalogger.