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- Video capture card: Seamless switching of four-in, one-out, four-in, one-out live broadcast stations at the same time[1]
01 HDMI multi-channel controller
I. Preface
This HDMI multi-channel video switching and acquisition module does not have a network interface, it has an infrared controller, and the following uses a microcontroller to record and simulate the infrared control signal, so as to add an automatic control network interface to this video switching and acquisition module.
2. IR LED signal analysis
The IR LED signal is first drawn from the inside for later signal analysis and acquisition.
Next, use an oscilloscope to observe the signal of the infrared LED of the controller, and analyze the amplitude and modulation frequency of the signal. In this way, it is convenient to use a single-chip microcomputer to decode and copy later. Fix the controller output signal on the breadboard and press the button to test the output signal. Let's start watching.
Using an oscilloscope for a single capture, you can see that the LED emits a signal with an amplitude of 1.9V with a modulated pulse signal. Unfold the waveform and you can see that the frequency of the modulated signal is 37.7kHz.
● IR Signal Characteristics:
Amplitude: 1.9V
调制频率：37.7kHz
3. Controller design
Design the controller, which is a AT32F421-based microcontroller circuit. The wireless controller is input via PIO. One infrared LED output port, one reading infrared remote control signal port, which is used to measure the original controller signal. The remote control signal is read and copied by software. The design of the PCB board is suitable for one minute of board making, and the circuit board is obtained after one minute, and the circuit board is very perfect.
AD\Test\2024\May\VideoCaptureF8P7.SchDoc
▲ Figure 1.3.1 Schematic diagram of the controller
Fourth, welding debugging
The circuit board is soldered, cleaned and then debugged. Next, hardware and software debugging is done.
5. Software development
By placing the circuit board on the debugging clip and using the probe clip to connect the AT-LINK to the circuit board, the ICP software can access the microcontroller, which provides the possibility for later software development.
Use Workbench to build the program framework, use Keil IDE to compile and download, and the LED on the board flashes, indicating that the initial program is working properly.
Set the timer1 so that it produces a 37.7kHz interrupt at two times, so that the input signal can be sampled twice in the interrupt, and a 37.7kHz square wave output can also be generated. It should be noted here that in the development of AT32 microcontroller, it is necessary to manually clean the interrupt flag in the interrupt program, otherwise the phenomenon of repeated triggering will occur. Here is the square wave output generated by the IO port, and the waveform is measured with an oscilloscope to finally determine the output square wave with a frequency of 37.67kHz.
In the interrupt program, the remote control signal is acquired, if the interrupt frequency is twice the modulation frequency, each modulation cycle can only be collected twice, which may be the acquired signal is at the edge of the signal, and the acquisition frequency is increased to 4 times, which can ensure that the high level of the collected pulse can be ensured. The acquired signals are recorded below.
6. Record the modulation signal
According to the acquired modulation signal, it is sent out through the infrared transmit port. It can be seen that the demodulated infrared signal corresponds to this time. An infrared code can take no more than 0.5 seconds. The time of the received IR code is recorded. It is then re-modulated and emitted, and it can be seen that it is consistent with the original IR signal. This signal is then driven to an infrared light-emitting diode. Put it on the HDMI quad switcher side, you can see that the video switching can now be completed normally. This shows that the function of remote control can be completed when the recorded signal is collected and then played. Place the infrared transmitting port on the receiving port of the switching module to form a control effect.
※Summary※
In this paper, the control commands of the infrared remote control are copied by using a single-chip microcomputer. It allows you to control the four-way HDMI video switcher. This constitutes an automatic video acquisition and editing system.
Resources
[1]
Video capture card, multi-camera live broadcast dedicated four-in, one-out broadcast station seamless switching, simultaneous four-screen capture: https://detail.tmall.com/item.htm?_u=1nvskcd8296&id=694436037244&spm=a1z09.2.0.0.25ac2e8df397ST