Hi, I like to wiretap my phone line. [sirens] NOT TO RECORD PRIVATE CONVERSATIONS! [sirens stop] Just to record my own conversations. Especially with phone scammers, in case there’s anything good for my other channel. In fact, is it legal? It is illegal with an exception where one of the parties to the private communication consents to the interception of that communication so Canadians can legally record their own conversations with other people. Okay, then that’s good enough for me. I’m safe in Canada. I can record my own conversations. Unless I don’t get consent to myself. I mean some of my personalities can be a bit crafty… [slap] What did you say? In any case, let’s see what the phone line is made of. I plug in this phone cable and I have it exposed on the other side The two lines are called tip and ring and as you can see there is 48 volt DC on them Which is a pretty harmless voltage mMMAAUUGHHH F**K!!! [quality content] It hurts! All right, I did check five years ago that I can’t take more than 12 volts on my tongue! But back in Iran, we had this building cleaner guy who was trying to help me find the live telephone lines by putting it on his tongue! And his reaction was like “mweh”. It was never as painful looking as it actually is! He set a bad example. Never set a bad example, there are idiots out there that will try what you did and will hurt themselves. Anyway, this DC level is pretty safe on skin *gets shocked* S**T! Kind of zapped me! Oh Yeah? No, why is it that I die a little every time you call? Well, obviously the ringing voltage is high. Let’s measure it using my awesome Keysight Scope! Which I’ll give away at the end of the video! Now if I probe this line you see 48 volt on a 50 volt scale and if I call home using my cell phone Yeah, you see a pretty artificial looking sine wave Although I guess all of them are artificial. So you see the ringing voltage is a bit above 160 volts peak-to-peak or around sixty volts RMS with a 20 Hz frequency So if you’re not careful, it could zap you now you might ask Why do we need such a high AC voltage to signal ringing? It’s because it’s a carryover from stone ages, when this had to drive a s**t bell on rotary phones. Our phone lines are designed to support classics. Now. Let’s see how my voice looks like on the scope See when I pick up the phone the 48 volt drops significantly to around 7 volts because per standard the phone has to load the line with a specific resistance around 390 Ohms. That’s how the switching center knows that you picked up the phone. Now if I get rid of DC and amplify the signal a little bit… “Hello! Hello!” “ooooOoOOoOOOOOOOO” It seems like a signal coming from the phone is around a maximum of 3 volts peak-to-peak and from the cell phone “ooOOoo hooOOoo HOOOOooOOoo” Is maximum around one volt peak-to-peak So as you see both voices are run on the same signal and to capture this I just need to send a one signal into my circuit What I like to do is to design a circuit that feeds these into my camera’s audio jack But it seems to me that if I plug this during an active call All I need is a single capacitor in series to separate the DC level on both sides. Well, let’s give it a try. I connected my headset to a series capacitor if you guys can see it there and it’s connected to the phone line and I’m gonna plug it in and See if I can hear a communication. Let’s dial. Oh OH S**T! Wait! F**K! S**T! Phew! I put 48 volts across this 16 volt capacitor Whew, it’s not even warm. Apparently the phone line can only deliver very little current, not enough to blow up my capacitor But in any case, let me make the phone call first and then plug this in “Hello, hello,” HAH! See I can clearly hear myself. Let me show you okay “Hello, hello, 1 2 3 4, can you hear me?” So all I need to do is to design a circuit that protects my camera against high voltage, reverse voltage, ringing voltage and can feed the audio into my camera. The last thing I want is for my camera to blow up. Now let’s check with an actual microphone to see what kind of audio voltage levels we are dealing with. Right now I set the microphone to its maximum gain so what you see here is actually pretty loud and is around one volt peak-to-peak and if I yell into it, “HoOoo ho hoOOo” Those voltage levels are already much higher than what I saw on the phone line Which means I can probably safely send those signals directly to my camera. Now, let’s design. [Mehdi is designing] And here is the circuit I designed! The phone lines go into a “FULL BRIDGE RECTIFIER” to prevent reverse polarity over our circuit, then we have some DC voltage isolation, some voltage division and some over voltage clamping and then the output goes straight into the camera. If you need more details check my website electroboom.com Okay, the circuit is all together. SssSs AAH! Okay, let me show you. Here’s the circuit The phone line on this side first goes into the [calm and composed] full bridge rectifier Then the rest of the circuit and the output goes to the audio jack here, which I’ll plug into the camera. Okay let’s see I am probing the audio jack output and you don’t see any trace of the 48 volt input and if I pick up the phone, you see the dial tone mixed with my voice and now if I dial home [dialing in progress] [phone ringing]You see the ringing signal which is a little bit over 1 volt peak-to-peak So this is pretty safe to feed into my camera Now I have switched my cameras and I’ve connected the audio jack into my camera while probing the signal. And all I need to do is to start recording and, uh, “Hello? Hello?” What happened there? Hello. Hello? Hello [start recording] [stop recording] What the hell? Why is the camera outputting some DC voltage when recording? [worried] “Hello? Hello?” Dammit, my circuit diodes are gonna clamp that! No [inaudible] I guess I’ll just add another capacitor here to isolate the DC from the camera from the circuit [signs heavily] It’s just another capacitor Okay, let’s plug it in again So far pretty eventless, let’s call home [ringing] Okay, it seems like everything is in order… The circuit is not warm… everything is good… [lamp falls] F**K! S**T! Stupid f**king lamp!
Where did this come from? Now here is the important part. Because the gain of my circuit is fixed, I have to go to the camera and make sure that the audio doesn’t clip by adjusting the camera gain. See? Now it’s good. “Hello, hello, 1 2 3” Now I just record on my camera and change the audio input to the phone line and die (dial home) *noise* [warning earrape] [ringing] [through the phone] Hello? Hello? You hear me now? It should be pretty loud. Uhh, let’s check the cell phone, [from cellphone]Hello? hello? Here’s my cell phone, I believe it’s a little bit softer. Damn, it sounds pretty good. We are ready to record. I just need an enclosure for it. And what’s ever better than a container filled with hot glue Well done maestro! ## Giveaway time!!! ## Good news everybody! Two things. First, I decided to open a new line of giveaway to schools for any kind of tools they might need, but don’t quite have the budget for. I thought this way one giveaway could help many kids learn. If I find sponsors like the awesome Keysight who would like to help you with the school giveaways, then great! Otherwise, I’ll put the generous support of my patrons at patreon.com/ElectroBOOM to good use to purchase tools, and make sure every month a school at least gets most of what they need I’m already greatly in debt of my patrons and want to make sure their generosity supports future generations in addition to my channel. So follow the school link in the description, read the instructions and enter your school for the draw. Any school that needs a tool anywhere in the world can enter, just as long as I can ship there. If YOU like to also support the school giveaways and my channel and be automatically in the giveaway draws, then don’t hesitate to join the patreons. The first school to get the Keysight scope is the Wick High School in United Kingdom. There was no draw for this one, of course. The physics teacher, Mr. Neil Mundt asked me for it to help encourage his kids to learn science, which started the whole idea of school giveaways. I thought to myself as the Queen herself puts it,
“That’s bloody brilliant!” So his school deserves to be first. And second, is the Keysight scope giveaway to my viewers and patrons You know, Keysight has helped me give away around 14 scopes so far! 16 with these two! So not only they design some great s**t, They are also great people! Make sure to subscribe to their channel for great knowledge on equipment use, and as usual patrons are automatically in the draw. For everyone else, please follow the viewer link in video description and good luck. Are we don- PHANG putha putha PHANG putha puhh PHANG [x2] PHANG putha putha PHANG putha putha PHANG putha PHANG putha putha PHANG putha puhh PHANG