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1  Using Arduino / Project Guidance / Re: AN7312 as amplifier - tape head , magnetic stripe on: April 13, 2014, 10:24:46 am
I was not sure about these connections as they looked optional for me:
  • ALC Time constant
  • ALC input
  • Phase compensation
  • NF
  • Ripple filter

Since I am going to keep it simple, I want to only use the minimal arrangement in order to  add additional things later in case.

The only necessary connections except for power supply for me seem to be:
  • Input of Channel 1/2
  • Output 1/2

Concerning decoupling, by now I know this when using a very variable load, one can add a decoupling capacitor (like 100nF) between Vcc and GND in order to avoid voltage dip (aka voltage sag) like when a motor starts as it consumes more power in that state of starting.

Unfortunately, I do not see this kind of need here where to use    decoupling capacitor.


If you could please explain these a bit more in detail.
2  Using Arduino / Project Guidance / Re: AN7312 as amplifier - tape head , magnetic stripe on: April 13, 2014, 09:53:29 am
Thank you.
This google search brought me to a site I have already seen, but couldn't find again anymore.
Magnetic stripes Part 1 « AndrewNohawk
Quote
[...] the one side you need a mono jack [...] which will go into the PC to record the audio. [...] The other side of the cable is simply wired to either side of the magnetic read head [...]
Using this I had no success as my MIC_in doesn't seem to work with this little voltages, however I already found out it worked using a known variable voltage each msec (toggling 0 ~ 4mV) which showed up on Audacity as a rectangular wave form.

Still I want to use the AN7312 as amplifier and maybe someone can help me with that. I already posted my circuit.
3  Using Arduino / Project Guidance / AN7312 as amplifier - tape head , magnetic stripe on: April 13, 2014, 09:06:59 am
Hello,

using the AN7312 (datasheet)    I want to amplify the signal of a tape head for Arduino's input.

Code:
    Arduino
      o A0
      |
      |
5VDC  |
(VCC) |
  o   |   .----------.
  |   |   |          |
  |   |   |          |
 .o---o---o-.    .---o--------.
 |  AN7312  |    |  CH1 CH2   |
 |          |    | Tape Head  |
 '----------'    '------------'
  |                    |
 ===                  ===
 GND                  GND

I already successfully checked the functionality of the tape head by measuring the voltage of CH1 with analog input and the result was 1 to 2, i.e. ca. 5 to 9 mV. However, this worked only with a strong magnet. My intention is to read a magnetic stripe.

Regarding the datasheet of AN7312, I am only using:
  • 14 - Vcc
  • 1 - GND
  • 4/11 - Output 1/2
  • 7/8 - Input 1/2
(unfortunately;some pins of the lower row have been broken , so I tried both the ch1 (=lower row) ,ch2(= upper row)  )

On Arduino's A0 I only see noise like when connecting nothing.

How do I construct the (audio) op amp for the tape head to read a magnetic stripe using Arduino?

Thanks for any hints on this smiley
4  Using Arduino / General Electronics / Re: SIM900 - LM2596 Step-down 5V>4V adjustable output voltage on: November 24, 2013, 07:21:48 am
Hello,
thank you for your finding.
I was first thinking about using  this SIM900 module and an UBLOX GPS for creating a GPS tracker with sending the position via internet (GPRS) to my computer.
Now I would prefer the TK102B because this is more compact and cheaper than building your own one.
If anyone wants to create a GPS tracker, I'd take
- the SIM900 module, not SIM900A  (35 USD, new version 60 USD)
- Ublox NEO6MV2 (ca. 11 EUR / 15 USD)
- some rechargable battery
- some enclosing

Anyway you need a SIM card with either cheap SMS charge or cheap Internet access. For Germany: I'd recommend Netzclub.
5  Using Arduino / General Electronics / Re: SIM900 - LM2596 Step-down 5V>4V adjustable output voltage on: November 23, 2013, 09:42:24 am
here (SIM900 GPRS/GMS Shield - LinkSprite Playgound) it is said:
Quote
       Voltage :   Min 4.8,    Typical 5.0,    Max    5.2    VDC
Quote
Power select - select the power supply for GPRS shield(external power or 5v of arduino)
that seems to be optional which power source to take, so I don't need to power it externally
Quote
current: max 450    mA
here (Arduino Playground - ArduinoPinCurrentLimitations) it sais:
Quote
Absolute Maximum Ratings:
DC Current VCC and GND Pins...... 200.0 mA

Does that mean I need to power it externally?
6  Using Arduino / General Electronics / Re: LM2596 Step-down 5V>4V adjustable output voltage on: November 23, 2013, 07:13:50 am
Now I am thinking about buying this module
http://www.ebay.de/itm/SIM900-GPRS-GMS-Shield-fixed-price-/200972757437?pt=US_Metal_Detector_Accessories
(ebay id = 200972757437, "SIM900 GPRS/GMS Shield (fixed price)", seller:  www_pcduino_com (385))

It seems to be some kind of Arduino shield that is made to be put onto an Arduino board, and this is being supplied with 5V maybe through some regulator to the SIM900 IC.
It got a WIKI page:
http://linksprite.com/wiki/index.php5?title=SIM900_GPRS/GMS_Shield

Is there any idea to recommend a specific one to me?
7  Using Arduino / General Electronics / Re: LM2596 Step-down 5V>4V adjustable output voltage on: November 23, 2013, 05:41:57 am
Thank you for the answers. I have read buyer reviews concerning the sim900a at alibaba in which it was said that the module had the European GSM frequencies supported - quad band - and is also said to work in Europe by the seller, some tests proved the contrary so it will not work in Europe  (it seems to be blocked by the european carriers).
I am now looking for alternative GSM modems working in Europe (900, 1800 MHz is what I need) and are compatible with either 5v or do not draw more than 1A whereby in the latter case I'd use the regulator.
8  Using Arduino / General Electronics / Re: LM2596 Step-down 5V>4V adjustable output voltage on: November 22, 2013, 10:27:50 am
Do you mean it   is not even possible because the voltages 5v (input)  and 4v (output) are too close together?
So my input voltage is 5v. Are there buck converters (step down) from 5v to 4v. I'd prefer some fixed ouput regulator, however think 4v is not that frequently used...
9  Using Arduino / General Electronics / Re: LM2596 Step-down 5V>4V adjustable output voltage on: November 22, 2013, 09:33:58 am
hello and thanks for the formula including the resistor values r1  and r2.
Unfortunately I do not know whether the ebay module linked
http://www.ebay.com/itm/400603204991
is there any possibility to adjust the output voltage because it also says "adjustable output voltage" ?
10  Using Arduino / Programming Questions / Re: VirtualWire wrapper around send function on: November 21, 2013, 03:11:51 pm
Thank you, this helped me out for the first issues.
11  Using Arduino / General Electronics / SIM900 - LM2596 Step-down 5V>4V adjustable output voltage on: November 21, 2013, 03:10:52 pm
Hello,

for some IC I need an input voltage 4V. It has TTL 3V3 Levels so I have a 5V>3V3 regulator and powering this with some 5V constant voltage power supply. Then it will transform 5V to 3v3 to supply ATmega328P (on a breadboard) and this will communicate with the module using 3v3 TTL I/O.

SIM900A-module.JPG > http://www.ebay.com/itm/281194207422

LM2596 : How to adjust the output voltage? It says:
Quote
http://www.ebay.com/itm/400603204991
Input voltage: 4V-35V
Output voltage: 1.23V-30V
and is
Quote
Switching frequency: 150KHz
somehow concerning this ?

http://www.ti.com/lit/ds/snvs124c/snvs124c.pdf

Thank you
12  Using Arduino / Programming Questions / Re: VirtualWire wrapper around send function on: November 16, 2013, 10:12:36 am
ok, so did I understand it correctly:
Code:
vw_send((uint8_t *)tmp, 1);
passes the address of "tmp" as read-only value as the first paramter to "vw_send"
And in the function header of "vw_send", there is written:
Code:
uint8_t vw_send(uint8_t* buf, uint8_t len)
after the data type of the first paramter, there is an asterisk, that means the first paramter is accessed via its address.
Additionally, it is expressed that buf is a unit8_t. However, later it is accessed as array like
Code:
buf[i]
So don't I have to declare that buf is actually an array of uint8_t ? What is the advantage of passing its address?

--------

I am trying to write a function sending 2 bytes at once.
This is my approach:
Quote
extern void vw_send_int(uint16_t x, boolean waittx=false);
extern boolean vw_get_int(uint16_t& x);
Quote
void vw_send_int(uint16_t x, boolean waittx /*=false*/)
{
  byte tmp[2];
  tmp[0] = x % 256;
  tmp[1] = x / 256;
  vw_send((uint8_t *)tmp, 2);
}

boolean vw_get_int(uint16_t& x)
{
  uint8_t buf[2];
  uint8_t buflen = 2;

  boolean result = vw_get_message(buf, &buflen);

  if (result)
    x = buf[0] + buf[1] * 256;

  return result;
}

Is there a possibility to simplify the process to split a 2 byte value into 2 one-byte values and also the other way round?
13  Using Arduino / Programming Questions / Re: VirtualWire wrapper around send function on: November 16, 2013, 09:36:08 am
Do you mean, i could directly call this function when sending a message instead of using a wrapper whose only difference is to accept char instead of byte?
14  Using Arduino / Programming Questions / Re: VirtualWire wrapper around send function on: November 16, 2013, 09:25:15 am
Concerning the function void "vw_send_string" I want a char array (C string) to be sent instead of a String.
I know that "vw_send" expects a pointer to be passed and a length of bytes beginning at this address to be sent.

I want a function call somehow like this:
Quote
char somestring[] = "Hello"; // automatically sets the size to 6 (5+1 for null termination)
vw_send_string(somestring);  // call with variable passed
vw_send_string("World");     // call with string passed

It should be able to simply send a string.

Thus I have to define a function somehow like this:
Quote
void vw_send_string(char string[])
But why should it be sufficient to
Quote
but how do I modify the function header to a char array instead of a String.
Change "String" to "char *".
I should have to send an array and I was explained that array has often to do with asterisk usage.

So is your recommendation to use the asterisk to point to that array instead of passing an array?


15  Using Arduino / Programming Questions / Re: VirtualWire wrapper around send function on: November 16, 2013, 08:36:00 am
Thank you very much for your detailed answer and I am glad to see you are also very familiar with VirtualWire.

Concerning your last answer:
I now understand very well how to use the ampersand like
Code:
get_byte(byte& b)

Where is the difference in using this and the asterisk?
So, when using the ampersand the address is sent and the function is able to change the passed variable.
For instance
Quote
function increase_value_by_999(int& x)
 { x += 999 }

int somevalue = 1;
increase_value_by_999(somevalue);
Serial.print(somevalue); // should send 1000 to Serial monitor

And the asterisk also sends the address of the variable? Sorry to ask again, but this is not clear yet for me.
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