How can I receive a time signal with an unmodified RTL-SDR USB TV Dongle here in Europe?
RTL-SDR Dongles are able to receive the frequency range 52-2200MHz.
Here in Europe, radio-controlled clocks receive DCF-77, a time signal broadcast on 77KHz, but as 77KHz is a bit lower than 52MHz, that's out.
The GPS L2 signal is at 1575.42 MHz, so that's within the dongle's range, but the signal is way too weak to be received with the TV antenna. An active GPS antenna is needed, and for providing the antenna with the power, I'd need to make some modifications to the electronics which I don't really want to do.
In the old age of analog TV broadcasting, we had Teletext / Videotext here in Germany, which contained a time signal, but these times are long gone.
ADS-B reception with a dongle works like a charm, but unfortunately they did not put in time or date bits into the data packets.
So: Does anybody have any idea where in the spectrum that can be received by an unmodified RTL-SDR dongle there is a time signal that could be easily decoded?
I'm well aware that getting time over the network via NTP, or via a GPS modem via NMEA 0183 would be way easier, but I'm curious and just want to play around with that dongle a bit. Precision is not important. +/- 2 seconds is fine. And I'd like to do it the SDR-way, so using the dongle in the originally intended way (as a DVB-T receiver using the original software) defeats the purpose (i.e. learning and DIY)
The GPS L2 signal is at 1575.42 MHz, so that's within the dongle's range, but the signal is way too weak to be received with the TV antenna. An active GPS antenna is needed, and for providing the antenna with the power, I'd need to make some modifications to the electronics which I don't really want to do.
Well, first of all, GPS is really weak, but it still works under the noise floor; that's something important to realize – I've seen it more than one time that people are worried because they can't see GPS on a PSD display. You won't; you'll need signal processing to recover it from all the noise.
The modifications aren't all that complicated; basically, you need a capacitor to let through the AC component to the RTL dongle, and a voltage source to feed the active antenna; the required component is usually called a bias-T.
Nevertheless, an active antenna will be necessary – your RTL dongle probably won't have a Noise Figure low enough to receive GPS signals on its own.
In the old age of analog TV broadcasting, we had Teletext / Videotext here in Germany, which contained a time signal, but these times are long gone.
True; haven't looked at local FM stations, but RDS might be the way to go – it can contain a clock/time signal; the German Wikipedia claims that mainly publicly owned stations transmit that information field.
Have a look at gr-rds; it's a GNU Radio implementation of the Radio Data System. If you don't have a working GNU Radio installation (yet), you might try out the GNU Radio LiveSDR Image, which contains a ready-to-use gr-rds.
Related
I would like to create the indoor positioning system. I hope the system can collect all beacon signal and create map automatically. However, I know that far away beacon maybe cannot detect. Therefore, is that possible to discovery far away beacon based on other beacon? That is, beacon can transfer their signal based on other beacon?
Sorry, but no, it is not possible to use a beacon to relay signals of more distant beacons. Bluetooth beacons are extremely simple devices that just transmit a unique identifier. They are transmit only, and therefore completely unaware of other beacons around them.
There is a question that can micro-controllers programmer damage micro-controllers in a way that they can't be programmed any more? (I have usb programmer)
This question came in my mind when i found out that my new-bought micro-controllers become unprogrammable after that i programmed them for some times, but except that they can't be programmed any more they work correctly in the way they have been programmed.
Thanks for reading.
If your AVR has power issues during programming, it is possible for its fuse bits to become messed up. You should make sure your batteries are fully charged (if applicable) and be careful not to disconnect power during programming.
If the AVR fuse bits that specify its clock source get corrupted and the AVR expects you to connect an external clock or crystal, but you do not have such a clock or crystal in your circuit, then the AVR will not have a clock signal and you be unable to program it.
Luckily, there is actually a way to revive such AVRs: you can get another microcontroller to generate a PWM signal and apply it to the XTAL2 or XTAL1 pin of your AVR as a low-speed clock signal (e.g. 100 kHz). Then use your programmer (configured to use a low enough ISP frequency like 2 kHz) to connect to the AVR and fix its fuse bits so it uses the correct clock source.
The Pololu USB AVR Programmer v2.1 has a feature to generate such clock signals. A procedure for reviving AVRs is documented in the "Using the clock output to revive AVRs" of that programmer's user's guide. There is at least one person who successfully revived an AVR using this principle. If you try it, please let me know whether it works for you!
In general, there are lots of other ways for microcontrollers to be damaged or destroyed depending on what you are doing, so you might consider posting the details of your setup to a more AVR-focused forum that allows free-form discussion instead of just a question/answer format.
(how) Is it possible to have the Eddysone-URL provide functionality, similar to NFC, that would have the user only within a close proximity be able to get the URL?
I've been testing using the eddystone-beacon library on the Intel Bluetooth 4 enabled Wifi card to send the signal successfully. But I find that I can receive the signal from far (20+m) away, when I'd like to limit it to within one meter.
The library has options to attenuate the power txPowerLevel: -22, // override TX Power Level, but I find that changing this only messes with the distance calculation, and not the ability to receive the signal.
Is this perhaps an issue with the hardware (maybe a dedicated USB would allow control?)
Eddystone-URL is not designed to work this way using Google's standard services. However, it is possible to do what you want if you have a dedicated app on the mobile device that detects the beacon.
If this is an option for you, then you won't want to reduce the transmitter power on your hardware device. Even if you get hardware that allows this, sending a very weak signal will lead to unpredictable minimum detection ranges of 3 feet or more on devices with strong receivers, and not detections at all (even if touching the beacon) on devices with weak receivers.
Instead, leave it at the maximum transmission power and then filter for a strong RSSI on the receiving device, showing the detection only when the RSSI meets a threshold. You'll still have trouble with varying strengths of receivers, but it is much more predictable. I have used this technique combined with a device database that tracks the strongest signal level seen for a device model, so I know what RSSI a specific device model will detect when it is right next to the beacon.
If you are game for this approach, you can use the Android Beacon Library to detect Eddytstone-URL for your app on Android devices and the iOS Beacon tools on iOS devices.
I have a thought, but am unsure how to execute it. I want to take a somewhat long usb cable and plug both ends into the same machine. Then I would like to send a signal from one end and time how long it would take to reach the other end. I think this should cause signal to arrive at different times and that would cause me to get random numbers.
Can someone suggest a language in which I could do this the quickest? I have zero experience in sending signals over usb and don't know where to start or how to start. Any help will be greatly appreciated.
I simply want to do this as a fun in home project, so I don't need anything official and just would like to see if this idea can work.
EDIT: What if I store the usb cable in liquid nitrogen or a substance just as cold in order to slow down the signal as much as possible (I have access to liquid nitrogen).
Sorry I can't comment (not enough rep), but the delay should always be the same through the wire. This might limit the true randomness of your numbers. Plus the acutal delay time in the wire might be shorter than even a CPU cycle.
If your operating system is Windows, you may run into this type of issue:
Why are .NET timers limited to 15 ms resolution?
Apparently the minimum time resolution on Windows is around 15ms.
EDIT: In response to your liquid nitrogen edit, according to these graphs, you may have more luck with heat! Interestingly enough...
Temperature vs Conductivity http://www.emeraldinsight.com/content_images/fig/1740240120008.png
I want to take a somewhat long usb cable and plug both ends into the same machine.
Won't work. A USB connection is always Host -> Device, a PC can only be Host. And the communication uses predictable 1 ms intervals - bad for randomness.
Some newer microcontrollers have both RNG and USB on chip, that way you can make a real USB RNG.
What if I store the usb cable in liquid nitrogen or a substance just as cold in order to slow down the signal
The signal would travel a tiny bit faster, as the resistance of the cable is lower.
I am looking to write an Arduino script that uses whatever audio signal is going to the speakers to create a physical visualization.
The Arduino is connected to the windows machine only through USB, so I need to use USB to find out what is being sent to the speakers. How would I access this information?
As of right now, the Arduino can only communicate with the computer via serial over USB. Things have changed with the new Arduino Uno, but the examples have not yet been released to show how to have the new Arduino act as other USB devices.
You would have to write something for the Windows box that monitor's the system audio and sends the info about it over serial to the Arduino, as long as you want it to only connect via USB.
There isn't a very good way to interface an audio signal to an Arduino without some external hardware.
One way to do it though would be to connect the audio line to a biased pin with a capacitor, then you could use the ADC directly. There will be pretty terrible dynamic range, but it only takes 3 passive parts. Running that through an opamp before going to the ADC pin could significantly improve dynamic range and provide a filtering opportunity (see below). Alternatively, you could switch on an on-chip voltage reference to use (typically 1-1.5 V) instead of the main supply.
It doesn't matter that much for a straight visualization, but the sample rate will not be good enough to capture the full spectral content of the audio (in addition to the poor dynamic range resolution). The default Arduino sample rate is 10 kHz(-ish...possibly asynchronous), so you will only get valid data if your signal is below 5 kHz, otherwise aliasing will muck it up. (If you write your own analog driver for the ATmega32P you could get up to 76 kHz sample rate with 8-bit samples)
Then to actually communicate that data to a computer, you can fairly easily throw all those ADC values onto the UART for the computer to pick up and process as it sees fit. An ATmega will not have the power to compute FFTs on the fly (what you'd do almost always do for a viz anyways).
Or to skip all that, connect the audio signal to your computer's sound card (or USB sound card...they're pretty nice) and use some audio driver.
There is a Java library for processing called ESS that lets you access audio out.