First Pat wrote on 20 February 2012 at 22:21

I've been looking at doing something like this, but notice there's no capacitor in your schematic. Is not there a 2V DC bias on the headphone input for condenser microphones? Would it be a good idea to eliminate that so your scope probe does not have a DC voltage on it?

Second Nico wrote on 21 February 2012 at 08:54

Hey Pat! Thanx for your comment. I'm aware, that there is no capacitive compensation in my circuit, as it is just a rudimentary way of measuring some higher voltages. But as far as I know, there is no capacitance in the input of said devices. Normally the capacitor for condenser microphones is built into the microphone itself, right inside the headset into the mic capsule. Which device do you mean?
But I do plan a second version of my test with compensation so that one can measure more accourately without the influence of the cables. But the problem is, that you need a different capacitance on each single devider. That would increase the whole circuit a lot and makes it more complex to rebuilt for others.

Third Pat wrote on 21 February 2012 15:58

I was not thinking of multiple caps, just one to DC couple the input to the phone (between the jack and the Zeners in your schematic).
If you take a voltmeter and put it across your scope probe I think you'll see ~ 2V? That voltage is present on the mic input to power a condenser element. In this application that is not desirable, so I was thinking a cap would solve the problem.

Of course this will impact low-frequency performance of the application scope, but this would be gene rally used for higher frequencies I assume.

Just to confirm, the scope as you have it set up, will not register DC anyway?

4th Nico wrote on 11 March 2012 at 13:00

Hi Pat, after thinking a while and several translation possibilities, I think I know what you mean. What concerns my devices, they do not power a condenser mic. Therefore no ~ 2V are present on the input. Maybe your device is different concerning that? Please let us know, Which device that is. For me and some others, my circuit works fine for DC and AC at any frequency supported by the input. Yes, right, DC as well. But for this purpose I would use a multimeter, not an osci.

5th Veena wrote on 16 March 2012 15:07

Hi,
I am Veena Parashuram from Bangalore, India.
I would like to buy your probing device. Could you please let me know how I can order it?

Thanks a lot
Veena

6th Ilan wrote on 21 March 2012 at 13:05

Hi

I own a Samsung Galaxy S2 cell phone and I want to use the 3.5mm microphone input jack.

Question: Can it measure DC signals? or just AC (audio signal ...)?

Thnx
Ilan

7th Nico wrote on 22 March 2012 08:59

Hi Veena, thanks for your interest, but I do not plan to sell it. I actually dont have time to mass produce probes. Therefore I published this guidance, so that everybody can build it his-or herself. It is really nothing complicated, try it and I will help you or find somebody, who can do it for you. Greetz, Nico

8th Nico wrote on 22 March 2012 at 10:04

Hi Ilan, I think you were confused by the previous speaker Pat Of course my sample and said all apps / programs are able to show DC signal. But please keep in mind, that this application is not the purpose of an oscilloscope! For that a multimeter would be much more comfortable and precise. A stable DC voltage would be shown as a simple horizontal line in the oscilloscope on, the amplitude shows you the value. I do not know, what the comment from pat means and if he owns the only device, that has a power output of 2V. My PC, my iPod and my Sony Ericsson Thurs not have this issue. I wrote an email to him, but he does not answer anymore. So please give it a try and let me know. Greetz, Nico

9th Tim wrote on 30 March 2012 11:28

Hi,
First many thanks for the guide.
But I have a question about your voltage divider. If I measure now so I burden the voltage divider and the ratio would change. eg I put an AC voltage to a 1k resistor and measure it with your probe, the voltage across the resistor. Then I'm in the ratio 2:1 is no longer so suddenly 1.2k to 1.2k in series, parallel to but 1.2 k 1k k and the two in series with 1.2 This change but the Verhätlnisse and my measurements are distorted. would not it make more sense zuwählen so much more resistance in the mega-region?
Or I'm on the wrong track?

Greetings Tim

10th Nils wrote at 01 April 2012 23:57

Hi, i am interested in making an oscilloscope for my android phone, but you stated that the max voltage on the mic input can be v 1.2 but you are using two zener diodes v 2.2, this wont damage the phone / pc when measuring Voltages higher then 2.1 v? I am also having difficulties finding Zeners v 2.2, as i am only able to find 2.7 + Zeners.

11th Nico wrote on May 07 April 2012 02:27

Hi Tim, yes, because you have right of course. A loaded voltage divider moves the splitter in the direction of the measuring input. However, all microphone inputs are device-specific manner and therefore difficult to consider a flat rate. The input resistance but moves all around your 47kOhm, which affects only the third decimal place. So I just ignored the times
In principle it is right to work even at higher frequencies with as high-impedance probes. But as will be shown in the instructions I have said, must be at most units of the total internal resistance of 1.2 ohms, otherwise a nice message like "this accessory is not supported". Try this with you some of that comes at you with a different resistor this message. If not, I advise you, of course, interpret the whole thing much higher impedance. Good luck!

12th Nico wrote on May 07 April 2012 02:46

Hi Nils, the statement about the 2.1 volts comes from Certain manufacturers of computer sound cards and is just a "guide only". The Android app Oscilloscope Pro even supports measuring up to 10 volts according to the settings. Only the manufacturer can tell, what your phone is really able to suffer. So I wanted to be on the save side and dont wanted to strain my phone with more than the conservative 1.2 volts. But for me it does not matter, Whether it is 2.0 or 2.2 volts. If I need a higher range, I have my divider. But if you go higher, please keep in mind, that the curve of a zener is not linear! It just begins at the nominal value. If you want it save, take the 2.0 zener. Greetz!

13th Oleg wrote on 21 April 2012 22:55

Can I get the apk file to e-mail because I can not find Market program. Chinese Tablet Android 2.2

14th Nico wrote on 22 April 2012 10:38

Hi Oleg,
I am not the author of the app. Please contact Nick Winder from http://nfxdevelopment.wordpress.com/
Most likely you can not see the app, because it is not made for your tablets or Android version.
Greetz