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1  Using Arduino / Project Guidance / Re: Portable project with LED matrix - power requirements on: August 06, 2014, 03:05:00 am

not a power expert, but depending on your needs, I would go for something like this:
Dirty cheap, available of the shelve and when you pair it with 2x3400mAH NCR18650B's like these:

You pack 6800 mAh in a package just a bit bigger than the 18650s themselves... Also all your charge electronics and 5 volt voltage regulator @2.1 AMPS are taken care off...

If you want to tinker yourself, I would suggest getting at least three 18650's/LiPO's in series with a switching regulator in between...
Off-the-shelve: Search for UBEC on ebay, like this:

Regards Dennis
2  Using Arduino / Project Guidance / Re: Buy List for a SMS serveur ? on: February 01, 2014, 07:52:38 am
Take a look at something like voipbuster (
Depending on where you live, an average SMS would cost you about 7 euro cents (I took France as a reference for you).
That would mean a break even between a gateway and a DIY service of more than 2000 text messages...

I'm of course not sure of your needs, but 2000 text messages for break even seems like a lot  smiley-grin
3  Using Arduino / Project Guidance / Re: Buy List for a SMS serveur ? on: February 01, 2014, 06:38:44 am
Not that I don't like a good hardware project, but I don't think this is the way to go.

If you want your webserver to send text messages, I think that an email2sms gateway, or some other online SMS service  is a far better solution.
For sure you can send e-mail from your server, so by using a gateway you are basically done.
There are also some webservice oriented SMS services, giving you even a bit more flexibility, at the cost of some extra programming.

In terms of costs, in total (hardware + GSM subscription + running costs (electricity etc.) using a simple gateway could very well be a cheaper solution, not to mention more reliable.

Just my 2 cents, if you want to go with a DIY solution, go for it!
4  Using Arduino / General Electronics / Re: powering with a 11v lipo battery on: May 17, 2013, 08:35:40 am
Don't use a 11v LiPo together with a lineair regulator.
The above calculation is even worse with a full LiPo.

Charged LiPos peak at 4.2 Volts per cell.
Therefore your max. voltage would be 4.2 * 3 = 12.6

If you want to use a 3 cell LiPo, get a switching regulator and attach to the 5 volt line of your arduino.
These regulators can be found cheap on ebay for instance:

(Just the first one I found, not a well thought out recommendation

A bit of a double post, now that I read the previous post better.
Oh well, just use a switching regulator smiley-wink
5  Using Arduino / Programming Questions / Re: led bar code simplify on: May 17, 2013, 08:21:24 am
Or even combine both suggestions above for even more simplicity:
for (unsigned char i = 0; i < 4; i++)
  digitalWrite (ledbar1[0], (a0c>i));

(Untested, but you get where I'm going)
6  Using Arduino / General Electronics / Re: IR Beam Interrupt on: May 02, 2013, 09:59:18 am
Hi LyonJK,

No problem.
Good luck with thinking this through!

Regards Dennis
7  Using Arduino / General Electronics / Re: IR Beam Interrupt on: May 02, 2013, 04:34:03 am
Hi LyonJK,

IR would also be as simple in terms of programming I guess, just a bit more tinkering to do on adjusting them properly.

However, I don't see how this would solve your problem.
If you open the door for someone, like a messenger, either you or the messenger (or both) will still interrupt the IR beam, also registering as a false entry / exit...

Only valid solution I can think of is using two beams a meter / 3 feet or so apart, and measuring timing and direction.
Something like:
Beam A is nearest to the door, Beam B furthest, both in your hallway.
If B is triggered first, then A and nothing triggered after that for a couple of minutes: exit
If A is triggered, then B and nothing triggered after that for a couple of minutes: entry

And make a filter for all other patterns (for instance, multiple readings of the same trigger, without the other in between count as simply one).

I think this should work for at least a single person going through the door.
If you have multiple people walking out / in the door after each other, you would probably need the last two readings from this setup to deal with direction...

So I would expect IR to be technically simple, but to deal with also detecting the difference between just opening the door and really leaving / entering, the main challenge would be in the software, not the hardware.

Regards Dennis
8  Using Arduino / General Electronics / Re: IR Beam Interrupt on: May 01, 2013, 10:29:02 am
If I understand you correctly, knowing that someone opened the door is already good enough.
How about using a reed switch like the ones found in most alarms?
They are easy to install as they are meant for the job, cheap as can be and also easy to use with an arduino, as it acts just like a switch.
See for instance, but there's probably tons more to find out there.
9  Using Arduino / General Electronics / Re: 433mhz rf transmitters. on: April 25, 2013, 05:01:13 am
Google for VirtualWire, like
I think you'll manage from there smiley
10  Using Arduino / Storage / Re: Arduino EEPROM Programmer: Burning a ROM image on: October 29, 2012, 02:41:00 pm
Nice that you figured it out yourself!
You need to indeed just send the raw binary data.

A couple of simple dos commands would have also sufficed:

mode COMXX: 9600,n,8,1
copy /b [FILE] COMXX:

Where you would replace [FILE] with your file and COMXX with your com port.

Or you could create a batch file, on which you can drag the ROM image (not tested, but you get the idea):
@echo off
mode COMXX: 9600,n,8,1
copy /b %1 COMXX:
11  Using Arduino / Storage / Re: Arduino EEPROM Programmer: Burning a ROM image on: October 28, 2012, 03:50:41 pm

I'm not familiar with programming EEPROMs, but seems to me you're almost there.
First I would recommend replacing this:
      } else {
      digitalWrite(AP[i], bitRead(A,i));
and losing the AD array all together.
Same can be done with the D loop and DD array.

As for reading serial data, you've already managed to use Serial communications, so all you would need (besides from perhaps something like error correction) would be replacing the line:
with something like:
    while (Serial.available()==0) delay(1);
    D =;

That would assume you would always send the full content of the EEPROM (8192 bytes) through the serial port.

Good luck!

Regards Dennis
12  Using Arduino / Audio / Re: Emulation of soundcard filters with Arduino on: October 25, 2012, 03:36:26 am
No, I don't.

However, if you look at the page you found yourself more carefully, you will see that everything is already in the schematic.
Apparently they use a "MCP6001" op amp as stated in the right of the schematic.
The filtering seems to be a worked out version of a simple low-pass filter.
(See for details about this.)

Also, if you check the blog they link too (, you will find the older version, which is easier to understand.

Good luck with your project!
13  Using Arduino / Audio / Re: New library for PWM playback from SD cards: SimpleSDAudio on: October 23, 2012, 03:31:13 pm
Hi Tuttut,

Great work, many thanks for this!!!

As for audio filtering, I've tested with a "Passive, first order low-pass RC filter", which seems to clean out most of the noise with just a resistor and a capacitor, see
I found a  1kohm resistor and a 2.2qf capacitor work out for me, but to be honest, I used a trial and error approach...
Not sure if this even comes in the neighborhood of your buffer approach, but I found the improvement more than adequate for my project.

Once again, many thanks!!!

Regards Dennis
14  Using Arduino / Audio / Re: Emulation of soundcard filters with Arduino on: October 23, 2012, 08:48:56 am

the analog inputs on the arduino only like positive voltages (between 0 volt and 5 Volt / Analog Reference Voltage), see
Filtering out DC will not solve your problem.

It does seem like your amplitude is quite low.
Probably your soundcard is more sensitive.
Although I'm definitely not an electronics expert, I would suggest at the very least checking the average output voltage.
That should be approximately 2.5Volts, giving you a nice average of 512 when using analogRead.
If it is below, you can set the analog reference voltage to something more usefull (your peak voltage), see for more info.
You could also try to give the signal the proper DC offset and amplitude, but that would require electronics knowledge which I don't have...

If you want to "filter" dc in software, that's also possible.
I used something similair to the code below to deal with a varying offset (not the actual code, and not tested, but this should work without much changes).
What this does is sample the last 4 readings, and check if the current reading deviates from this average by a certain threshold.
The code could also be used with more samples (up to 32 without changing all the integers to longs / unsigned ints).

For me that worked fine, but it depends a lot on the amplitude of your signal.

Hope this helps...

Regards Dennis
const int analogPin = 9;
const int analogThreshold = 40;
bool analogTriggered = false;

void setup() {
  pinMode(analogPin, INPUT);

void loop () {
  if (analogTriggered) {
    // Trigger code

void analogWorker() {
  static int analogAvg = 512;
  static int analogValues[] = { 512, 512, 512, 512 };  // Average last 4 values
  static int analogCounter = 0;
  static int analogTotal = 2048;  // Fill with total of analogValues[] (4x512)
  static int readOut;
  readOut = analogRead(analogPin); 
  analogTotal -= analogValues[analogCounter];
  analogValues[analogCounter] = readOut;
  analogTotal += readOut;
  analogAvg = analogTotal >> 2;  // Fast division by 4
  analogTriggered =
    ((readOut>analogAvg+analogThreshold) ||
  analogCounter = (analogCounter+1) % 4;  // Cycle through values
15  Using Arduino / Audio / Re: simple audio input for arduino on: October 19, 2012, 06:19:46 am
I'm still having issues but can u send me  your schematic and code PLEASE Id really appreciate it 

I'm no expert on the topic, but I think you could use,8559.0.html as a start.
On the blog refered to there: you can find the schematics and source.

Good luck with your project!

Regards Dennis
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