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16  Community / Exhibition / Gallery / Re: BlinkIT on: January 06, 2013, 08:22:02 am
laser beam is on my mind too. It would be very cool to use as an unusual and alternative wireless transfer technology. I think doing some basic encoding, such as Manchester encoding, on the signal will improve robustness a whole lot. That will probably help when doing longer distance.

Are you willing to share the code? I am curious.

Again, nice work!

17  Community / Exhibition / Gallery / Re: Yet another Humidity and Temperature logger on: January 06, 2013, 08:05:07 am

on the other hand the analog hygrometer agrees on the new value.

18  Community / Exhibition / Gallery / Re: Yet another Humidity and Temperature logger on: January 06, 2013, 08:02:28 am

.... and there I jinxed it *sigh*

Went back to upload the latest version of the data file (have it running) and then I see a sudden jump of almost 10% relative humidity!
Checkout the jump at 12:34

This is 35min after I closed all windows and everything should be stable really.

Need to take a look at the debug printouts to see what is going on.

Regardless, it works a lot better than before.


19  Community / Exhibition / Gallery / Re: Yet another Humidity and Temperature logger on: January 06, 2013, 07:45:54 am

Success! :-)

I did some reading and some thinking to understand it on my own and came up with a slightly modified implementation from your code hint, but basically it is the same (2d interpolation).

Did a test run, including a big ventilation of the apartment (opening all windows) and kept a manual log from my reference setup (analog hygrometer and digital themometer) and it looks really good! The setup keeps within +/- 0.4C from the reference thermometer and a few % from what the analog hygrometer shows.

The new graphs are available on the same URL as before:

With the old approach, I would get strange bumps in the reading while ventilating and in the settling period following that. I guess because I would jump between temperature rows in the lookup table as the temperature dropped and rose again.

Thanks again for your patience and helpful advice!


20  Community / Exhibition / Gallery / Re: Yet another Humidity and Temperature logger on: January 05, 2013, 10:16:16 am

the URL to the lookup table is actually in the source code in the sketch, just by the lookup table itself. :-)
It's from the data sheet for the EFS-10 humidity sensor. Here:

I got the sensor as a present and really don't know so much about it other than it being sold by It is the first time I use it and I can't say it was very easy. I am not used to generating AC signals to drive a sensor and then having to work out the impendance of it from the (volt) value you get from analogRead() didn't make it easier. Now add 2d-interpolation to that and everything gets a little too complex for a beginner like myself.

The LM335 is a common and easy-to-use temperaure sensor in a three-pin transistor like package. Didn't give me any trouble at all and pretty much worked the first time I hooked it up.

I am trying to incorporate your suggestions now BTW. Will report back once I have it working, hopefully tonight.


21  Community / Exhibition / Gallery / Re: Yet another Humidity and Temperature logger on: January 05, 2013, 08:51:49 am
great advice! Thanks!

I too have been thinking about interpolating in 2d, but made it a priority to get all moving parts working together first.

Good points about the small stuff as well. Will work them into the next version, as I implement you 2d suggestion.

Many thanks!

22  Community / Exhibition / Gallery / Re: Bitlash Commander: Web UI toolkit for Arduino on: January 05, 2013, 02:55:33 am

Nice work!

Seeing the thread above, I recalled a problem with node and serial port communication I ran into a couple of weeks ago.

It seems like node-serialport has some kind of issue on Mac OSX.
Reported here

Could that be lawm's problem?

23  Community / Exhibition / Gallery / Re: BlinkIT on: January 05, 2013, 02:36:31 am
please post the code and some more detail if you can. I am interested to have a look. Are you using any kind if encoding? Looking at the video, it seems like a long pulse high marks the beginning of transfer. Have you considered the issue of ambient light (daylight), or is it too early at this stage?

24  Community / Exhibition / Gallery / Re: Yet another Humidity and Temperature logger on: January 04, 2013, 05:51:57 pm


Next, I hope to rig everything on the Data Logging shield from Adafruit to remove the need to use my laptop as data collector.

Anything I should think about?



25  Community / Exhibition / Gallery / Yet another Humidity and Temperature logger on: January 04, 2013, 05:49:12 pm

just a quick word from me to share my design and code for a setup I built over Christmas to measure relative humidity in our apartment.

Code, images and circuit documentation can be found here:

Sample data from logging the output (with sub sequent sub sampling) can be viewed here:

It is common to find apartments without proper ventilation in Germany (where I live). This is not even legal in Sweden (where I come from). Without proper ventilation, you face a whole range of issues with the indoor climate, bad air and particles is just a start, condense and mold is at the other end of the spectrum. This triggered the idea to let my next project be a hygrometer. That and a wish to build a nice balcony greenhouse this year. :-)

Looking for input on approaches you find a whole lot of questions and discussions in this forum, but not so much solid information, so that's why I decided to post my project here. It far from perfect, but it is at least a working end-to-end circuit and sketch to look at and perhaps get inspired by.

I believe my algorithm to measure the relative humidity has some issues, but I haven't gotten to a point where I can say what and why. Just notice a few odd things and "jumps" in my data. Ultimately it might be down to the crude approach of using a lookup table and interpolation to come up with the value. Input more than welcome!

Another thing to note is the (unusual?) way the EFS-10 humidity sensor works. You have to drive it with a square wave and then the impedance of the sensor will vary with the relative humidity. Not the most straight forward thing to use, at least if you are a inexperienced like me. Still haven't found any good sources for dealing with such sensors. If you have any pointers, it would be very welcome.

Many thanks to MarkT who provided the crucial pointers and code snippets to get me on the right track!


26  Using Arduino / Sensors / Re: Sensor value calculation on: January 02, 2013, 03:03:47 pm
your sensor seems to be working a whole lot like the EFS-10 humidity sensor, which I just recently managed to hook up to the Arduino and get to work thanks to the good people at this forum (yes, that's you MarkT :-).

The EFS-10 works on the same principle - you generate a square wave to feed it and you cannot use DC.

The code to drive it is available here, along with some documentation

This is the circuit I use an LM135 to measure temperature.

The square wave is generated by switching two digital pins on and off at the right frequency.

I am sure there is room for improvements, but I think it might be a starting point at least.

Good luck!


27  Using Arduino / Sensors / Re: Advice on hooking up the EFS-10 Humidity Sensor? on: January 02, 2013, 10:42:28 am

Hey MarkT,
just a note to say thanks for the help!

Using you advice and the code as a starting point, I managed to put something together which works quite nice. It still has some issues at some break points where it is several % off in the reading. Haven't tracked it down yet, but I am convinced it is down to the way I round off the temperature and do look-ups to finally interpolate a value, using a table from the EFS-10 data sheet.

If you are interested, I have documented the result here, including the code.

Thanks again!

28  Using Arduino / Sensors / Re: Advice on hooking up the EFS-10 Humidity Sensor? on: December 10, 2012, 03:18:11 pm

good point about the interrupt. Not a major issue for me. At this point I am just looking to take a reading, store it and to display it on an LCD with buttons to step back in time to see previous readings. Later on, there might be some serial sending of values to a host, but that is later, if ever.

Also, the thing with the input multiplexer was new to me. Very valuable info! Need to do some more reading and try to find a block diagram over the components. Still only had a vague idea about available timers, prescalers, interrupts and similar things (watchdog?).

Thanks again!

29  Using Arduino / Sensors / Re: Advice on hooking up the EFS-10 Humidity Sensor? on: December 10, 2012, 10:18:18 am

Thank you very much!

This is exactly the kind of advice I was thinking about.

Some clever tricks in there for me to look closer into, like reading analog twice and just throwing away the first read.

Ideally it would have been great to be able to set some kind of interrupt and throw this routine in there. Don't like the busy loop approach, but that's more advanced I guess.

Thanks again!

30  Using Arduino / Sensors / Advice on hooking up the EFS-10 Humidity Sensor? on: December 09, 2012, 03:45:03 pm

Hi guys,
my electronics is a little rusty and I am hoping you might be able to get me started in the right direction here.
I am trying to build a simple logger to register the relative humidity in a room at home (indoors). The problem boils down to understanding how to read the impedance of the sensor I believe.

The sensor I have is the EFS-10 Humidity Sensor from Hygrosens. I got it from and the datasheet is available here:

I not a total rookie and have already built a couple of simple projects, reading resistive sensors, but this one is based on the impedance and I have no clue how to hook it up.

The datasheet says:
The measurement of impedance should be done with an AC current (without DC-offset). The recommended operating frequency is 1 kHz for a measuring voltage of maximum 1Veff.

Anyone who can help me understand this a little bit better?

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