Light Sensing RF Transmitter circuit

Circuit Today,I would like to present in RF transmitter with light control which can apply to your electronic project next time.

This transmitter is very similar to the simple radio transmitter. The other is the resistance of the photo placed in series with R1(47k).

  This may be a thermistor or other sensor with variable resistance. The tone frequency is transmitted varies depending on the amount of light on the photocell (Photoresistor).

L1 use 20 to 30 turn of 24 to 32 GA. Magnet wire close wound around a 1 / 8 to 1 / 4 inch diameter non-conducting form and tapped 1 / 3 of the way to one side.

The device is connected to the emitter of Q1(2N2222) .
The user should be able to receive the signal from the transmitter to a standard VHF or FM. By increasing the number of turns on L1, the RF frequency entirely collapsed in the AM band.

Light activated circuit

Today,We have two simple circuit is a transistor switch to the base of the transistor with a voltage divider. The voltage divider consists of two resistors. The first is the 100K Potentiometer 1K plus protective layer resistance. Secondly, the resistance of LDR. This is the schematic representation of the circuit:

When the light changes on the surface of the LDR, LDR is the resistance. The more light, the lower the resistance of the LDR, the less friction, the lower the voltage over it. The less light, the greater the resistance and thus the greater the voltage across it.

Part List

D1 = 1N914
Q1=2N2222 OR similar NPN transistor
R1 =Photoresistor
R2=50K Variable Resistor
R3=1K
Relay = 5 to 6 volt relay.

When the voltage increases, the SD of the 2N2222 transistor and thus the ICE increases accordingly, until the current is sufficient to activate the relay.

The amount of light that can be changed to activate the relay by a change in the 100k potentiometer. In short, any change in the potentiometer to the voltage loss of the LDR effects because they are both members of the voltage divider are described above.

The 1N4001 diode is used to eliminate stress again, if the relay is turned off. It is very important to the diode, as can be damaged without the transistor.
Before serving work as far as the activation. It will not detect a problem, dark or light or operate the relay, but it will be a problem if the relays are released. At this point, the circuit has a large hysteresis. Therefore, we must continue to strengthen the signal before we apply to the switching transistor.

We will BC517 NPN Darlington transistor pair. Should we 2N2222 between him and the LDR, as the following circuit shows:   

Dark activated circuit

This addition increases the sensitivity of the circuit. The hysteresis window is decreased significantly, but there is still an area known as the relay is activated, it will not be rotated by the same amount of light that existed just prior to activation.
Only an adjustment and that would (of course) potentiometer. Your goal is to operate the circuit when the relay is equal to or less light to the predefined value. The easiest way to do this is as follows:

Let the LDR by the amount of light illuminates you. Hold the potentiometer in the highest value. Then start slowly turning the potentiometer and reduce drag. If you “click” of the relay listen to find your reference. From that moment every time the light is less than or equal to (or more if the circuit is turned on the light “as configured) is to light that you have created this preference is enabled the relay.

Video Activated Relay circuit

If you want  the tuner you need to build the tuner by yourself ? 
The relay contactor output was connecting to electronic circuit by under control.

What is that mean? Can You directly connect the relay to a socket ? and the TV can straight away plug in to the socket? 

For the electronic circuit diagram which is only DC voltage , but i think the tv need AC , Yes?

So,do you need to put a transfomer ? where should you put ? how to decided which kind of transformer to be used?

I think normally is 12Volt or 9Volt transformer? Yes.

Electronic Part List

1. R1, R2   10K 1/4 W Resistor 
2. R3   1K 1/4 W Resistor 
3. R4   33K 1/4 W Resistor 
3. C1  1uF Electrolytic Capacitor 
4. Q1, Q2, Q3   2N2222 NPN Transistor 2N3904 NPN Transistor
5. D1, D2, D3   1N4148 Diode 
6. K1   9V Relay 
7. J1   RCA Jack 

Remark:
1. For you  will be take the circuit to switch for control mains voltage, it should be enclosed in a case.

2. This electronic circuit may be also work with most line level audio, however you may have to change the resistance value of R1 .

Power Off Relay Timer Circuit

      The circuit on the left is a common collector or emitter follower and has the advantage of one less part since a resistor is not needed in series with the transistor base. However the voltage across the relay coil will be two diode drops less than the supply voltage, or about 11 volts for a 12.5 volt input. The common emitter configuration on the right offers the advantage of the full supply voltage across the load for most of the delay time, which makes the relay pull-in and drop-out voltages less of a concern but requires an extra resistor in series with transistor base. The common emitter (circuit on the right) is the better circuit since the series base resistor can be selected to obtain the desired delay time whereas the capacitor must be selected for the common collector (or an additional resistor used in parallel with the capacitor). The time delay for the common emitter will be approximately 3 time constants or 3*R*C. The capacitor/resistor values can be worked out from the relay coil current and transistor gain. For example a 120 ohm relay coil will draw 100 mA at 12 volts and assumming a transistor gain of 30, the base current will be 100/30 = 3 mA. The voltage across the resistor will be the supply voltage minus two diode drops or 12-1.4 = 10.6. The resistor value will be the voltage/current = 10.6/0.003 = 3533 or about 3.6K. The capacitor value for a 15 second delay will be 15/3R = 1327 uF. We can use a standard 1000 uF capacitor and increase the resistor proportionally to get 15 seconds.