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?
[...] 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.
The data sheet contains a typical application circuit diagram, which shows a fair number of resistors and capacitors associated with the chip. Yet your breadboard has none of these. Why do you think you can ignore them?
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.
I can think of many reasons why some of the capacitors (in particular) are not optional. Amplifiers tend to oscillate if not properly decoupled, and the gain of the playback amplifier is set by the feedback circuit between pins 11 and 9 (4 and 6). Furthermore the graph of Gvo vs. frequency suggests that the capacitors on pins 6 & 9 are particularly important.
If you want to find the minimum configuration that works, start with a known working configuration and remove components until it ceases to function properly. If you have lost pins from the chip, that may not be possible.
Just a note: it is very bad practice to use a permanent magnet on a tape head!
I think this is a bit of an understatement. @Karlok,
As it appears that you have little experience with electronics (based on connecting an AC audio signal DIRECTLY to the arduino WITHOUT any capacitors) I would advise you stop drawing conclusions based on no experience with electronics. It is quite possible you have already damaged you tape head by exposing it to a magnet.
First the most obvious sin: Connecting an AC audio signal directly to arduino input without a coupling cap. In order for you to even begin to understand why this is wrong, you would need to understand the difference between ac and dc, which apparently , you don't. Let's keep it simple. The capacitor acts as a bridge between these two very different kinds of signals. Second sin: Putting a strong magnet close to a tape magnetic head. In order for you to even begin to understand why this is wrong you would need to understand magnetic field theory , flux density , field strength, and units such as gauss, webers, teslas , oersteds, which obviously is beyond the scope of this post. Suffice it to say, putting a strong magnet close to a device that has been carefully manufactured so as to possess very sensitive magnetic properties is bad. Don't do it. Third: Decoupling caps: Your conclusion (summary)-"only circuits that use motors need decoupling caps"
to avoid voltage dip (aka voltage sag) like when a motor starts
I am sorry to have to tell you this but ALL electronic circuits (at least digital, and many analog) use decoupling caps. It has nothing to do with motors. We obviously can't get into a discussion of capacitor theory here but let's keep it simple. A small value capacitor such as a 0.01uF or 0.1uF and even up to a 1uF present a path of least resistance for high frequency spikes, which for your sake we will just call "glitches" (a term electronics professional generally only use when talking to laymen) , thus shunting the spike to ground and eliminating the "noise" in the circuit. Tape head pre-amps live in a world where everything is small (signal wise) and there is always unwanted noise. The decoupling caps help eliminate that. Forth: Supply voltage. I see you are operating the chip on 5V. No doubt you looked at the datasheet , or perhaps the first line of it and did some simple math , like 5V < 14V, therefore 5V is ok. End of story. Not quite. If you bothered to look at the other specs you would have noted that with a supply voltage of 14V (ALMOST THREE TIMES 5V) the output voltage is ONLY (typically) 1.2 V. So tell me, What is 1.2V/3 ? Yeah, about 400mV . If your lucky you might get an analog reading of oh 80 out of 1023. Fifth: What troubles me the most is that after all the comments that were posted in response to your original post, your last post contains no questions about or mention of a COUPLING CAP. Do you know what a coupling cap is ? No , of course not. It is necessary to couple the AC audio output of the amplifier to the DC input of the arduino . I would recommend a 1uF axial non-polarize cap. These are readily available (RadioShack) , maybe not if you're in Germany. Let us know if there is anything else we can do to be of help. We're here 27/7/365.
If this approach doesn't work, you can try this circuit:
