Closed-circuit television (CCTV) uses video cameras to transmit signals to specific monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point-to-point wireless links. CCTV is often used for surveillance in areas that need security,such as banks, casinos, shops, departmental stores and airports or military installations.

Here is a remote-controlled CCTV switcher circuit to monitor six cameras on a single or dual monitor/TV. Then salient features of this switcher are:

1. Cameras: Six cameras with one way audio (audio incoming only)

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2. Operation: Fully remote-controlled (infrared commander)

3. Front display: LCD to display the camera selected and all other functions parameters

4. Camera selection: Manual (you can select any camera of your choice by pressing number keys or camera up/down keys on the remote) and auto (the switcher selects the cameras one by one and holds videos of each camera till the preprogrammed time)

5. Auto mode: You can change ‘on’ time of each camera (hold time) individually through the remote. Time can be programmed from 0 to 255 seconds.

6. Camera bypass: You can set any camera in bypass mode by entering 0-second ‘on’ time for cameras which you want to bypass or don’t want to watch during auto mode.

7. Audio: One-way audio. In this model, you can hear the audio from the camera selected by the switcher.

8. Video: Two video-out RCA sockets with 75-ohm impedance 1Vp-p are available at the rear panel of the master unit. You can connect two monitors in these sockets.

9. Other features: Wide input voltage range, long-range infrared remote commander, microcontroller-based design supported with CMOS digital integrated circuits, liquid-crystal display to monitor the status and bilateral digital MOS switches for switching the analogue video/audio signals from cameras.

At the heart of the circuit is Microchip’s PIC16F72 microcontroller, which controls all the functions described in the design. Its pin configuration is shown in Fig.1.

Fig.1: Pin configuration of PIC16F72 microcontroller in PDIP package
Fig.1: Pin configuration of PIC16F72 microcontroller in PDIP package

The circuit

Fig.2 shows the main control circuit of the camera switcher. In this circuit, PIC16F72 microcontroller controls all the functions such as interfacing/initialising the LCD to display all the desired characters on the screen, decoding the RC-5 command on pressing the required keys of the remote control and providing high logic to enable corresponding bilateral CMOS analogue switches to connect the video signal from cameras to the video-output socket and audio signals to the power amplifier of the corresponding camera selected from the remote. Here we have used the remote control of an LG TV (remote code No. 6710V00079B). It is readily available in the market.

Fig.2: CCTV switcher circuit

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A remote sensor is connected to port RB0 (pin 21), called interrupt port, of the controller and the software initialises interrupt routines along with timer-0 interrupt to decode the RC-5 command.

Any transmission from the remote consists of two start bits, one toggle bit, 5-bit address and 6-bit command. Here we have not used the 5-bit address. A biphase-modulated bit can be thought of as two separate bits that are always the inverse of each other. A logical zero is represented by a ‘10’ pattern on the IR input, while a logical one is represented by a ‘01’ pattern. That is basically used to decode the received message.

Toggle bit is a particular property of the RC-5 protocol. This bit changes polarity every time you press a key and will remain unchanged as long as you hold the key. That enables the receiver to detect released keys, which helps to eliminate key bounces. We have also used this bit to detect so that if any key is kept pressed for a long time, the routine detects the command once, keeps the value in a general-purpose register called ‘passdummy’ (refer to ‘.asm’ file), and does not process and store any further command till the remote key is released. The stored RC-5 command value in register ‘passdummy’ is used to perform the necessary function given in the source code.

The LCD shows the camera number selected from the remote and mode of operation (auto/manual).

For camera-hold time set for auto mode and other display text information, please see the LCD screenshot in Fig.3. Use of the LCD makes the project more user-friendly.

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All the cameras are to be connected to SK1 through SK6 (5-pin DIN connector) as shown in the circuit diagram.The extreme right and left pins are for 12V positive and negative supply (to be fed from the regulated power supply of the main switcher) for the built-in camera module. The 12 V power supply is permanently connected to all the cameras. Audio and video signals from the cameras are selected using switch pairs S2a-S2b through S7a-S7b (built inside IC2 through IC4) and fed to the audio power amplifier and video output sockets, respectively.

Each IC has four CMOS bilateral switches for transmission or multiplexing of analogue or digital signals. It is pin-to-pin compatible with IC CD4016, but has much lower ‘on’ resistance, which is relatively constant over the input signal range.

Video and audio signals from SK1 (camera 1) are connected to S2a and S2b, respectively, and both enable pins (to switch on both the switches) are connected to port RC7 (pin 18) of the microcontroller. Similarly, audio and video signals from SK2 to SK6 are connected to IC2 through IC4 and then to port C of IC1 as shown in Table 1.

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Enable pins of switch pairs S2a-S2b, S3a-S3b, S4a-S4b, S5a-S5b, S6a-S6b and S7a-S7b of IC2 through IC4 are shorted to each other and fed to the corresponding port of Port C as shown in Table I. The microcontroller provides high logic at Port-C pins to switch on a particular camera. The truth table for Port C is shown in Table II.

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Immediately after switching on the mains, the standby LED (LED7) connected to Port-C pin RC3 glows and the LCD shows the welcome page (refer to the LCD screenshot).

On pressing the power key on the remote, the standby LED turns off and the LCD shows which camera is ‘on,’ in which mode it is now and default hold time for the corresponding camera in ‘Auto’ mode.

As described above, pins of Port C (RC0, RC1, RC4-RC7) are connected to IC2 through IC4 for selecting the camera to be switched on. LED1 through LED6 are used to check the logic status of Port C. Pressing keys ‘1’ through ‘6’ on the remote makes the corresponding LEDs (LED1 through LED6) glow,indicating ‘on’ condition of the cameras (CAM-1 through CAM-6).

Fig. 3: Screenshots of LCD
Fig. 3: Screenshots of LCD

Here a 16-character, 2-line LCD is used in 4-bit mode. Data lines D4 through D7 of the LCD are connected to Port-B pins RB4 through RB7. Enable (EN) and reset (RS) pins are connected to RB2 and RB3 pins, respectively, and the read/write (R/W) pin is connected to ground as we have used the LCD in writing mode only. Preset VR1 (10-kilo-ohm) is used for setting the LCD character contrast.

Power supply

A simple circuit for regulated supply (shown in Fig.4) is used here. The +12V regulated output is used to power all the six cameras, IC2 through IC4 and IC5 and fed to another 7805 voltage regulator (IC7) to get the regulated +5V output for the microcontroller (IC1) and the LCD.

The current rating of the transformer should be around 2A, on the current consumption of the cameras. Use a good-quality heat-sink for both the regulators.

Fig. 4: Circuit for regulated power supply
Fig. 4: Circuit for regulated power supply

Power amplifier

A simple power amplifier (see Fig.5) is used to amplify the sound signal from the cameras and hear it on a small speaker.

Fig.5: Circuit diagram of power amplifier
Fig.5: Circuit diagram of power amplifier

The audio power amplifier is built around IC UTC820 (IC5). UTC820 is a monolithic integrated circuit audio amplifier delivering an output of 1.2 watts at 9V on an 8-ohm speaker load with 10 per cent total harmonic distortion (THD) and good ripple rejection. It is designed for audio-frequency class-B amplifier with a wide operating supply voltage range of 3V to 14V and minimum external components.

The pin configuration of IC UTC820 is shown in Fig.6.2. Components at pin 2 of the IC5 decide closed-loop voltage gain (dB) of the amplifier. Here a 47-ohm resistor (R11) and a 22μF capacitor (C12) are used and, with these values, about 45dB closed-loop voltage gain is achieved. You can reduce the component values for more gain but it’s not required here as maximum gain of 75m dB is possible. Capacitor C10 (100μF) connected between pins 5 and 7 of IC5 is used for boot strap and improving the low-frequency signal. The amplifier output at pin 5 is connected to the speaker via C13. The audio signal from the cameras is fed to input pin 3 of the IC via volume control VR2 (10-kilo-ohm), capacitor C17 and resistor R13. Here the output power is limited to about 500 mW at 8-ohm load approximately, so use of a good-quality 6.4cm speaker is recommended.

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Fig.6: Pin diagram of UTC820 audio power amplifier
Fig.6: Pin diagram of UTC820 audio power amplifier

Functions of remote control keys

The functions of various remote keys are shown in Fig.7.

Fig.7: Remote control of LG TV
Fig.7: Remote control of LG TV

Power on/off key. Press it once to switch on the switcher and press again to turn off or keep the switcher in standby mode and vice versa. (AC mains should be ‘on’ in both the cases.)

Camera selection key. Select any of the six cameras manually by pressing any of the numerical keys ‘1’ through ‘6’ once. For example, to select camera-3 press ‘3’ on the remote, and to select camera-5 press ‘5’ on the remote.

Auto/manual. By default, the microcontroller sets the mode of selection to manual. (In that case, you have to select the cameras by pressing the number keys or the camera up/down keys.) To change to automatic selection (auto) mode, press ‘mute’ key and the switcher selects the cameras one by one automatically. Pressing this key again will return the mode of selection to manual, and vice versa.

Camera up key (PRΔ key). By pressing the camera-up key, the switcher selects the next camera. For example, if the LCD is showing camera-2, pressing this key once makes the switcher jump to camera-3. Each successive pressing of this key will make the switcher jump to the next camera.

Camera down key (PR∇ key). By pressing the camera-down key, the switcher selects the preceding camera. For example, if the LCD is showing camera-4, pressing this key once makes the switcher jump back to camera-3. On each successive pressing of this key, the switcher jumps back to the previous camera.By pressing the camera-up key, the switcher selects the next camera. For example, if the LCD is showing camera- 2, pressing this key once makes the switcher jump to camera-3. Each successive pressing of this key will make the switcher jump to the next camera. Camera down key (PR∇ key). By pressing the camera-down key, the switcher selects the preceding camera. For example, if the LCD is showing camera-4, pressing this key once makes the switcher jump back to camera-3. On each successive pressing of this key, the switcher jumps back to the previous camera.

Time set up/down key (Vol+/Vol– key). In auto mode, the switcher selects the cameras one by one and the picture of the selected camera is held up for a certain time. By default, the microcontroller sets this hold time as 5 seconds. You can change this time for each camera individually from 0 to 255 seconds.

To change this time, press the edit key (TV/AV) once. The switcher goes to the edit mode. Select the camera (for which you want to change the time) by pressing the camera up/down key. On each successive pressing of the time set up key, the time increments up to 255 seconds maximum.

On each successive pressing of the time set-down key, the time decrements up to zero. If you set 0-second time for any camera, the switcher bypasses this camera during selection in auto mode. For example, if you set the time as 0-second for camera-3, in auto mode, the switcher selects camera-1, camera-2, camera-4, camera-5 and camera-6. Here the switcher bypasses camera-3. This function is useful if you want to skip certain cameras.

Edit key (TV/AV). To change the camera hold-up time for ‘auto mode,’ enter ‘edit’ mode first by pressing this key once and then set the desired time by pressing the time up/down key as described above. To exit edit mode after setting the time, press the same key on the remote once again. The controller goes back to manual mode.

Testing and troubleshooting

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After assembling the circuit without microcontroller, apply the power using ‘on’/’off’ switch S1. Check the DC voltage at pin 3 of regulator IC7. It should be +5V. Check the same voltage at pins1 and 20 of the base of IC1. Now, switch off the power, insert the microcontroller in its base and recheck all the connections from the PCB to the LCD and IR sensor TSOP1738. On applying the power, page-1 and page-2 text should display on the LCD screen. Using the remote, switch on the switcher and change the functional status on the LCD by referring to CCTV switcher remote commander (shown in Fig. 7) and LCD screenshots (shown in Fig. 3). Adjust VR1 for maximum contrast on the LCD. If you don’t get any output on the LCD, troubleshoot as follows:

1. No output on the LCD. Switch off the power and check continuity between the LCD and various pins of IC1 and regulator IC as shown in the schematic diagram. If the connections are Ok, switch on the power, vary VR1 and check the voltage at pin 3 of the LCD (0V to 5V).

2. No backlight on the LCD. Check the voltage at pin 15 (+5V) and pin 16 (0V) of the LCD.

3. Page 1/page 2 is shown on the screen but the remote commander doesn’t work (nothing happens on pressing functional keys of the remote). Check the supply at pin 2 of the IR sensor. It should be +5V. If +5V is available at pin 2, check the voltage at pin 3 of the IR sensor. If there is no voltage at pin 3, replace the IR sensor or check the PCB, etc for shorting.

Once the LCD shows page-1 and page-2 text properly and the remote commander is working, switch off the power and then switch it on again using S1. Now the LCD should show page-1 and page-2 as shown in Fig. 3. At the same time, pin 14 of the MCU should go high (+5V) and the power standby LED should glow. Now press ‘Power’ key on the remote. Pin 14 of the MCU should go low and the standby LED should turn off, and vice versa, on pressing the same key again. If this doesn’t happen, replace the microcontroller.

Connect LED1 through LED6 to connector CON1. Press ‘Power’ key on the remote to switch on the switcher. Page-3 text should appear on the LCD, showing camera-1 is ‘on,’ the switcher is in manual mode and the default time of camera hold for auto mode. At the same time, Port-C pin RC7 should go high and LED1 should glow. Select other cameras either by pressing keys 1 through 6 or camera up/down keys of the remote and check whether the corresponding LEDs (LED1 through LED6) are glowing (refer to Port-C truth table). Simultaneously, page-3 should show the corresponding camera number accordingly. If the LEDs don’t glow according to the truth table, replace the microcontroller.

When camera-1 is selected, the LCD should show camera-1 and LED1 should glow. If the monitor does not show the video of camera-1, or you hear no audio from the power amplifier, check 5V logic at pins 5 and 6 of IC4. If there is no voltage at these pins, check the availability of 0.6V at the base of transistor T5, +5V at its emitter and +12V at its collector. Follow the same procedure for all other cameras and their corresponding switching circuits.

Software

The source program is written in Assembly language and compiled using MPASM tool suite.

Construction

A single-side, solder-side PCB layout for the microcontroller-based remote controlled six-camera CCTV switcher and its component layout is given below for download.

Connect CCTV cameras in the sockets provided (SK1 through SK6). Also connect the LCD and remaining components (as shown in Fig.2) and +5V and +12V from the power supply circuit. Now a welcome message will appear. Press ‘Power’ key on the remote to start the switcher.

EFY note. The source code is available on the link given below.

Download PCB and component layout PDFs: click here

Download source code: click here

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