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1  Using Arduino / Project Guidance / Re: How to detect depletions in a soft surface like fine grained sand or flour? on: July 17, 2014, 06:47:05 am
Quote
If you read the light level on the area where there is no indent and then where there is an indent the difference should always be apparent

You are right! It's of course only the difference in signal that matters (indent/no indent), not the actual level, so if there is sufficient light to make a reading, it should kind of work itself out. The ambient light won't change significantly during a read pass, so that is no factor at all (or shouldn't be).

Worst case, I could just reserve two spots for calibration; one with an indent and one without. I could then take two readings with known outcomes and calibrate the levels accordingly.

I think I have all the parts needed to make a simple test. Excited now. This might actually work!

Erasing will be the next challenge, but my plan there is simple enough: Always clear the full surface and then re-write the last values again. You can imagine it as having a long surface and then I advance it for each change in value and write the full bytes each time. Once I reach the end, I just rewind and "scrape" the surface to erase all previously written indents.

In a way, it will be like a small journaled file system, as you can trace each record change until you have to reset.

Anders




2  Using Arduino / Project Guidance / Re: How to detect depletions in a soft surface like fine grained sand or flour? on: July 17, 2014, 02:38:28 am

Quote from: Robin2
maybe all you need is an Light Dependent Resistor that can "see" the difference in the light reflected from the flat surface and from the indentations.

Yes! This is my thinking as well. I don't really need the fine resolution of a luminosity sensor. I just need an on/off reading.
I will thinking that instead of a light-sensitive resistor, I could perhaps use a photo transistor or even a photo diode.

I guess one would have to somehow hook it up with a capacitor and then take a reading?

My fear is that it will be too unreliable though, due to influence from background light levels (daylight level or night).

Given that, it might be better to just buy two the ready-made sensors and use one to measure background levels and compensate for that in the measurment from an identical sensor.


Anders
3  Using Arduino / Project Guidance / Re: How to detect depletions in a soft surface like fine grained sand or flour? on: July 17, 2014, 01:46:29 am
Quote from: Robin2
Could you use something like clay rather than a powder and have a device that can feel the indentations?
Yes and no.
Quote from: Anders2009
I would have to switch to a firmer material, such as clay, but then  erasing becomes harder.


Regarding pegs, yes, I have several alternative ideas (pegs, non-connected switches, perls, ...), but I like the ephemeral quality of the sand. It would contrast with the normal expectation of longevity of data in an external storage.

I think I will have a go with the monochrome intensity sensor. It looks like it could provide a viable path.

Thanks!

Anders
4  Using Arduino / Project Guidance / Re: How to detect depletions in a soft surface like fine grained sand or flour? on: July 16, 2014, 03:46:49 pm
Many thanks!

Yes, this is probably the most feasible approach.

5  Using Arduino / Project Guidance / Re: How to detect depletions in a soft surface like fine grained sand or flour? on: July 16, 2014, 03:39:02 pm
Not really.

I was hoping just to read depletions as they are seen in the picture.

What "color sensor" are you thinking of? Maybe it  is still worth trying?
6  Using Arduino / Project Guidance / Re: How to detect depletions in a soft surface like fine grained sand or flour? on: July 16, 2014, 03:33:26 pm
Ok,
That confirms my initial analysis. Sound doesn't have good enough resolution I think. Sand and flour also absorb sound quite well.

Feeling is tough too. As you say, it will most likely cause more depletion, or possibly destroy the real ones. For that to work, I would have to switch to a firmer material, such as clay, but then  erasing becomes harder.


Do you think using a photo transistor or photo diode, possibly in combination with an LED could be worth exploring?
7  Using Arduino / Project Guidance / How to detect depletions in a soft surface like fine grained sand or flour? on: July 16, 2014, 03:09:13 pm
Hello,
I am starting to plan a project where I want to make a non-magnetic external storage device based on depletions in fine grained sand, or possibly flour. Ideally, it should have an analog or very low-tech feel to it. The total storage capacity isn't important. I am aiming for a few bytes of storage, perhaps enough to store the current time.

I believe I can solve most of it using regular components, but I am struggling to come up with a simple and preferably robust sensor to detect the depletions.

Using a camera and to take a photo and then run the image through a bunch of filters to process it would perhaps be one approach, but not only is it light dependent (and light changes during the day), but also it also feels crude. A camera would not be in the analog/low-tech spirit of the project. Arduino + image processing isn't a great combination either.

Is there a simple approach that I might have overlooked?

Examples



8  Community / Exhibition / Gallery / Re: Made my own TwitterClient and I think it's better than the example one on: January 30, 2013, 05:23:18 am
Is there also a way to display my twitter feed (to display tweets from those I'm following)?

What you are looking for is the Home Timline
https://dev.twitter.com/docs/api/1/get/statuses/home_timeline
9  Community / Exhibition / Gallery / Re: Made my own TwitterClient and I think it's better than the example one on: January 29, 2013, 10:18:16 am


Code:
Good point, but sometimes it's just fun to have all in one solutions.

That is true and fun is one of the most important factors to consider. Why else would one have an Arduino hobby?

10  Community / Exhibition / Gallery / Re: Made my own TwitterClient and I think it's better than the example one on: January 29, 2013, 05:17:54 am
Nice work and thanks for sharing!

I have been playing with a similar idea for control purposes, but never actually built any of it.

A trick I find could help a lot to simplify the on-board Arduino logic would be to put a service in-between the Arduino and the Twitter API to act as a proxy and format translator.

The idea would be that you can use the right tool for the right job. Calling a REST webservice, parsing the results and doing something with the data is a piece of cake in most "internet languages", like Java, JavaScript, Ruby or PHP. With a such a proxy in place, you could re-format the response from Twitter into something very Arduino-friendly to save valuable CPU and RAM. It would also give you a separation of concerns and provide a place to add more advanced features like caching of results and adding in more sources without having to change the Arduino program.

Hosting of the translator proxy could be done on a server of yours, or on an application hosting service like the examples below.
http://www.heroku.com/
or http://nodejitsu.com/

Anders
11  Community / Exhibition / Gallery / Re: Manchester encoding library for RF links. on: January 25, 2013, 03:08:21 pm
Thanks,
I figured so.

Have the new mchr3k version running now. Had some trouble getting it to work as his example code does not compile... :-/

On the other hand, most of them were minor errors.

Have put together a rig with a laser and a photodiode and sending Manchester encoded data across. Too bad it doesn't decode at this point. Need to do a whole lot of debugging now.

Anders
12  Using Arduino / General Electronics / Re: Help calculate Rb for controlling laser using transistor on: January 20, 2013, 11:22:36 am


The working circuit:


13  Using Arduino / General Electronics / Re: Help calculate Rb for controlling laser using transistor on: January 20, 2013, 11:13:40 am
Ok,
so the datasheet for the laser module says
Working current: Min 10mA, Typical 20mA, Max 25mA

This gives me:
  • Ic = 20mA = 0.020A
  • Ib = Ic/10 = 0.002A
  • Rb = Vs/Ib = 5/0.002 = 2500 Ohm

Tried with a 2.7k Ohm and nothing happened.

Then I put in a fresh transistor, figuring I might have blown the old one after all the experimentation and it WORKS!

Where did you the magic number 10?
The datasheet for the transistor says hFE DC current gain 200 (minimum).

Many thanks!

Anders
14  Using Arduino / General Electronics / Re: Help calculate Rb for controlling laser using transistor on: January 20, 2013, 10:39:48 am

Hi,
yes, the laser module is 5V compatible (says 4.5V typical) and it lights up when connected directly over the 5V source.
It is one of these: http://www.seeedstudio.com/depot/5mw-laser-module-emitter-red-point-p-72.html?cPath=156_161

The 5V comes from a breadboard power supply.
http://www.seeedstudio.com/depot/5v33v-breadboard-power-supply-p-566.html?cPath=155

It is very strange, I too noticed the pinout and I am pretty sure I have it right.
I also guesstimated the same range as you, but I have had no luck. Tried the following values for R1
39 Ohm
175 Ohm
1K Ohm
10K Ohm

Maybe I managed to blow the transistor... need to switch to another one to double check.

Can't figure out why it's not working. Must be something silly.

Anders



15  Using Arduino / General Electronics / Help calculate Rb for controlling laser using transistor on: January 20, 2013, 09:51:24 am

Hello,
I am trying to use a BC547B NPN transistor as a switch to control a 5mW red laser, but I can't get it to work.

I believe it is because I have the wrong resistor to control the current on the base.

Does anyone here know how I can calculate R1 in the sketch below?
Please ignore the laser component name (QED123), it is just a side effect of picking a random LED component to symbolize my laser.




I am unfortunately stuck. Have tried random values for R1, but no luck.

Anders
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