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31  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?



32  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!


33  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!


34  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!

35  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!

36  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!

37  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?

38  Using Arduino / Project Guidance / Re: Log Data to SD Card, Wirelessly Transfer Data to PC on: September 21, 2011, 02:44:29 pm
I'm by no means an expert, but your project sounds feasible.

Personally I would start right way to get the sampling and storing done, then as soon as the "official" Arduino WiFi shield comes out (announced the other day at the Maker Faire) I would buy one of those and get started on the data transfer problem.

Of course you could get any of the existing WiFi shields as well, but why do that when you can be cool with the new and hot one very soon. ;-)

Good luck!

39  Topics / Device Hacking / Feasibility: Fa. Assmann Universa 80 as external storage device? on: September 04, 2011, 09:07:38 am
I just found this odd-looking device on and it seems like it is some kind of giant floppy disk, but originally intended for audio.

Anyone has experience with this, or similar devices?

1 - What is it?

2 - How does it work?

3 - Could it in theory be used/hacked into an external storage device for the Arduino?
Idea: Control play/stop/record using with digital outs. Use Manchester encoding to read/write data.

Only a couple of hours left on the auction, so early input is appreciated. :-)

Thanks in advance!/Anders

40  Community / Bar Sport / Re: Books worth reading on: July 08, 2011, 01:10:00 am
K&R C.

I really liked Zen and the Art of Motorcycle Maintenance, but I admit it probably doesn't do much for Arduino development.


K&R is certainly a classic. Regarding the other book, one should not underestimate the influence of litterature and culture as a source of inspiration. I still remember stumbling upon Count Zero and Neuromancer (W. Gibson) way back in 1987. Count Zero was just out then. I was into the C64 demo scene and dreaming about a Amiga 500. In a way, those books contributed to my later career choice! They were just so cool! :-)

41  Community / Bar Sport / Books worth reading on: July 07, 2011, 08:46:14 am
I haven't counted, but I would bet that 8 out of 10 questions on this forum begin with some variation of "I'm totally new to electronics and programming ...". Being quite new to this world myself, I have been looking around for sources of knowledge and I thought I'd share two books that I have found to be very useful, even if they don't deal with the Arduino specifically.

The first one is Making Things Move, DIY Mechanisms for Inverntors, Hobbyists and Artists by Dustyn Roberts.
It's a great book that is very hands on and easy to grasp, while still providing you with enough depth to understand the underlying principles. It provided me with mental tools and courage to go on and try my own ideas. A great and easy read!

The second one is Practical Electronics For Inventors (2nd edition), by Paul Scherz. Among other things, this book demystified all those capacitors that "inexplicably" show up in more or less every circuit you will find. I bought it as a backup option when ordering the classic The Art Of Electronics, by Horowitz and Hill. This is indeed a thorough book, but I found Practical Electronics For Inventors to be much more useful for me. Having both doesn't hurt though.

What do you read?


42  Topics / Science and Measurement / Re: Brewing thermostat on: July 07, 2011, 08:26:43 am
I've no idea specifically why it didn't work, but generally I can say that my experience is that if all connections are fine (triple checked and measured), you should have a look at the power supply. It is one of the things that also changes when moving off from the breadboard and into "reality". Powering from an USB, or desktop power supply with nice smooth voltage and steady current is something completely different than a dodgy old car battery, solar cell or whatever you end up connecting you thing to in the end.

43  Using Arduino / Programming Questions / Re: Sequencer groove on: July 03, 2011, 02:31:18 am
I think you need to restructure and break up your code first. When that is done, you can go into more advanced optimizations if needed.

As mentioned early on in this thread, you should restructure your code so that reading inputs is a separate step from acting on the inputs. This way you can easily gain cycles just by skipping some actions and performing them only every N:th loop, or every N:th millis (better).

44  Using Arduino / Programming Questions / Re: Best serial terminal for MacOSX? on: July 03, 2011, 02:06:37 am
Two good tips, thanks!
45  Using Arduino / Programming Questions / Best serial terminal for MacOSX? on: July 02, 2011, 03:32:54 pm
this might be the wrong part of the forum as it is not directly related to programming, but maybe to the related topic "debugging". ;-)

Anyway, for debugging and serial interaction with the Arduino I have been using the "Serial Monitor" in the ArduinoIDE and sometimes the screen command, but I was wondering if there are better/alternative tools available.

I have been looking at the iSerialTerm (URL below), but before I buy, I would like to know what alternatives people are using on the Mac.

Any favorites out there?


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