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Tuesday, December 27, 2016
Tuesday, December 20, 2016
Sunday, April 13, 2014
Wireless FM Transmitter Circuit
With MAX2606 we can make a small mono fm transmitter. It is build with MAX2606 and covers at least 20m with 1.5 m long copper wire antenna. You can use this transmitter as an oscillator but change the 1000pF capacitor from the antenna with 15pF.
MAX2606 transmitter output power is -10dBm, that means something around 100µW (micro-watts) = 0.0001W. Of course this is very low, that’s why we recommend you to use an auxiliary power amplifier if you want to build a more powerfull transmitter based on MAX2606. You can find a few fm power amplifiers on electroschematics.com so please use the search box.
MAX2606 transmitter output power is -10dBm, that means something around 100µW (micro-watts) = 0.0001W. Of course this is very low, that’s why we recommend you to use an auxiliary power amplifier if you want to build a more powerfull transmitter based on MAX2606. You can find a few fm power amplifiers on electroschematics.com so please use the search box.
Max2606 transmitter circuit diagram
Long Range FM Transmitter
This is very stable, harmonic free, long range fm transmitter circuit
which can be used for fm frequencies between 88 and 108 MHz. This can
cover 5km range (long distance). It has a very stable oscillator because
you use LM7809 stabilizer which is a 9V stabilized power supply for T1
transistor and for frequency adjustment that can be achieved by using
the 10K linear potentiometer. The output power of this long range rf
transmitter is around 1W but can be higher if you use transistors like
KT920A, BLX65, BLY81, 2N3553, 2SC1970, 2SC1971…
T1 is used as an oscillator stage to deliver a low power stable frequency. To adjust the freq. use the 10k linear potentiometer like this: if you trim down, towards ground, the freq. will drop and if you adjust it toward + it will rise. Basically the potentiometer is used as a variable power supply for the two BB139 varicap diodes. Those two diodes act like a variable capacitor when you adjust the pot. By varying the diode capacitance the L1 + diodes circuit makes a resonance circuit for T1. You can use transistors like BF199, BF214 but do not use BCs. At this moment you don’t have yet the long range fm transmitter because the power is quite low, no more than 0.5 mW.
T4 is a preamplifier for the fm transmitter and is used as a voltage power rf amplifier and will deliver enough power to the final T5 transistor. As you can see T4 has a capacitor trimmer in its collector, this is used to make a resonance circuit that will force T4 to amplify better and get rid of those unwanted harmonics. L2 and L3 coils must be at 90 degrees angle one to another, this is to avoid frequency and parasite coupling.
The final stage of the long range rf transmitter is equiped with any rf power transistor that has at least 1 watt output power. Use transistors like 2N3866, 2N4427, 2N3553, BLX65, KT920A, 2N3375, BLY81, 2SC1970 or 2SC1971 if you want to have a pro fm transmitter with enough power to cover a long range area. If you use 2N2219 you will get no more than 400mW. Use a good heatsink for the T5 transistor as it gets a little hot. Use a good 12V/1Amp minimum stabilized power supply.
Long range fm transmitter circuit diagram
click on the schematic image for larger view
T1 = T2 = T3 = T4 = BF199
T5 = 2N3866, 2N4427 or 2SC1970 for 1Watt / 2SC1971, BLX65, BLY81, KT920A or 2N3553 for 1.5 to 2W power.
L1 = 5 turns / 0.6mm / 4mm silvered copper
L2 = 6 turns / 0.8mm / 6mm enamelled copper
L3 = 3 turns / 1mm / 7mm silvered copper
L4 = 6 turns / 1mm / 6mm enamelled copper
L5 = 4 turns / 1mm / 7mm silvered copper
Use silvered copper for L3 and L5 if you want to obtain better characteristics.
Then continue to build the rest of the rf transmitter, use proper shielding as indicated in the circuit schematic. When you finished the transmitter construction connect the antena or better a 50 or 75 Ω resistive load and use this rf probe, you can use 1N4148 diode instead of the probe diode.
Adjust again the 10k pot to desired freq. and then go to T4 stage and trim the first collector trimmer for maximum voltage indication on the multimeter. Then continue with the next trimmer and so on. Then go back to the first trimmer and readjust again untill you obtain the highest voltage on the multimeter. For 1 watt rf power you can measure a 12 to 16 Voltage. The formula is P (in watt) is equal to U2 / Z, where Z is 150 for 75Ω resistor or 100 for 50Ω resistor, but you must remember that the real rf power is lower.
After those adjustment, if everything is going well connect the antenna, continue using the rf probe, readjust again all the trimmers starting from T3. Make sure you don’t have harmonics, check your TV and radio set to see if there is disturbance on the band. Check this in another room, far away from the fm transmitter or antenna.
That’s all folks
… This is my design for a long range transmiter and is working well. I
used 2SC1971 which has a 12dB power gain in 88 … 108 MHz band, this is
around 15 times rf amplification. As T4 delivers around 80 to 100 mW of
rf power the final stage has enough power to deliver between 1 to 2W
depending the transistor usage.
T1 is used as an oscillator stage to deliver a low power stable frequency. To adjust the freq. use the 10k linear potentiometer like this: if you trim down, towards ground, the freq. will drop and if you adjust it toward + it will rise. Basically the potentiometer is used as a variable power supply for the two BB139 varicap diodes. Those two diodes act like a variable capacitor when you adjust the pot. By varying the diode capacitance the L1 + diodes circuit makes a resonance circuit for T1. You can use transistors like BF199, BF214 but do not use BCs. At this moment you don’t have yet the long range fm transmitter because the power is quite low, no more than 0.5 mW.
How does long range fm transmitter works
Make sure to encase the oscillator stage in a metallic shield to prevent parasite frequencies destabilizing the oscillating stage.T2 and T3 works as a buffer stage, T2 as a voltage amplifier and T3 as a current amp. This buffer stage is very important for freq stabilization because is a tampon circuit between the oscillator and the preamp and final amplifier. It is well known that poor transmitter designs tend to modify freq. as you adjust the final stage. With this T2, T3 stage this won’t happen anymore!
T4 is a preamplifier for the fm transmitter and is used as a voltage power rf amplifier and will deliver enough power to the final T5 transistor. As you can see T4 has a capacitor trimmer in its collector, this is used to make a resonance circuit that will force T4 to amplify better and get rid of those unwanted harmonics. L2 and L3 coils must be at 90 degrees angle one to another, this is to avoid frequency and parasite coupling.
The final stage of the long range rf transmitter is equiped with any rf power transistor that has at least 1 watt output power. Use transistors like 2N3866, 2N4427, 2N3553, BLX65, KT920A, 2N3375, BLY81, 2SC1970 or 2SC1971 if you want to have a pro fm transmitter with enough power to cover a long range area. If you use 2N2219 you will get no more than 400mW. Use a good heatsink for the T5 transistor as it gets a little hot. Use a good 12V/1Amp minimum stabilized power supply.
Long range fm transmitter circuit diagram
click on the schematic image for larger view
T1 = T2 = T3 = T4 = BF199
T5 = 2N3866, 2N4427 or 2SC1970 for 1Watt / 2SC1971, BLX65, BLY81, KT920A or 2N3553 for 1.5 to 2W power.
L1 = 5 turns / 0.6mm / 4mm silvered copper
L2 = 6 turns / 0.8mm / 6mm enamelled copper
L3 = 3 turns / 1mm / 7mm silvered copper
L4 = 6 turns / 1mm / 6mm enamelled copper
L5 = 4 turns / 1mm / 7mm silvered copper
Use silvered copper for L3 and L5 if you want to obtain better characteristics.
Adjustments of the long range transmitter
Start by construction the oscillator stage, solder a small wire to T1 10pF capacitor out and listening to a fm receiver, trim the 10k pot untill you can “hear” a blank noise or if you plug in an audio source you can hear the music. With a 70cm wire you can cover a 2 – 3 meter area just with the oscillator stage.Then continue to build the rest of the rf transmitter, use proper shielding as indicated in the circuit schematic. When you finished the transmitter construction connect the antena or better a 50 or 75 Ω resistive load and use this rf probe, you can use 1N4148 diode instead of the probe diode.
Adjust again the 10k pot to desired freq. and then go to T4 stage and trim the first collector trimmer for maximum voltage indication on the multimeter. Then continue with the next trimmer and so on. Then go back to the first trimmer and readjust again untill you obtain the highest voltage on the multimeter. For 1 watt rf power you can measure a 12 to 16 Voltage. The formula is P (in watt) is equal to U2 / Z, where Z is 150 for 75Ω resistor or 100 for 50Ω resistor, but you must remember that the real rf power is lower.
After those adjustment, if everything is going well connect the antenna, continue using the rf probe, readjust again all the trimmers starting from T3. Make sure you don’t have harmonics, check your TV and radio set to see if there is disturbance on the band. Check this in another room, far away from the fm transmitter or antenna.
That’s all folks
… This is my design for a long range transmiter and is working well. I
used 2SC1971 which has a 12dB power gain in 88 … 108 MHz band, this is
around 15 times rf amplification. As T4 delivers around 80 to 100 mW of
rf power the final stage has enough power to deliver between 1 to 2W
depending the transistor usage.
Good FM Transmitter Circuit
This house FM transmitter for your stereo or any other amplifier
provides a good signal strength up to a distance of 500 meters with a
power output of about 200 mW. It works off a 9V battery.
The audio-frequency modulation stage is built around transistor BF494 (T1), which is wired as a VHF oscillator and modulates the audio signal present at the base. Using preset VR1, you can adjust the audio signal level.
Audio FM transmitter circuit diagram :
The VHF frequency is decided by coil L1 and variable capacitor VC1. Reduce the value of VR2 to have a greater power output.
The next stage is built around transistor BC548 (T2), which serves as a Class-A power amplifier. This stage is inductively coupled to the audio-frequency modulation stage. The antenna matching network consists of variable capacitor VC2 and capacitor C9. Adjust VC2 for the maximum transmission of power or signal strength at the receiver.
If you design a good pcb layout you can use it as a car fm transmitter.
For frequency stability, use a regulated DC power supply and house the transmitter inside a metallic cabinet. For higher antenna gain, use a telescopic antenna in place of the simple wire. Coils L1 and L2 are to be wound over the same air core such that windings for coil L2 start from the end point for coil L1. Coil winding
details are given below:
L1: 5 turns of 24 SWG wire closely wound over a 5mm dia. air core
L2: 2 turns of 24 SWG wire closely wound over the 5mm dia. air core
L3: 7 turns of 24 SWG wire closely wound over a 4mm dia. air core
L4: 5 turns of 28 SWG wire on an intermediate-frequency transmitter (IFT) ferrite core
Check the related posts for some stereo fm transmitter circuits.
The audio-frequency modulation stage is built around transistor BF494 (T1), which is wired as a VHF oscillator and modulates the audio signal present at the base. Using preset VR1, you can adjust the audio signal level.
Audio FM transmitter circuit diagram :
The VHF frequency is decided by coil L1 and variable capacitor VC1. Reduce the value of VR2 to have a greater power output.
The next stage is built around transistor BC548 (T2), which serves as a Class-A power amplifier. This stage is inductively coupled to the audio-frequency modulation stage. The antenna matching network consists of variable capacitor VC2 and capacitor C9. Adjust VC2 for the maximum transmission of power or signal strength at the receiver.
If you design a good pcb layout you can use it as a car fm transmitter.
For frequency stability, use a regulated DC power supply and house the transmitter inside a metallic cabinet. For higher antenna gain, use a telescopic antenna in place of the simple wire. Coils L1 and L2 are to be wound over the same air core such that windings for coil L2 start from the end point for coil L1. Coil winding
details are given below:
L1: 5 turns of 24 SWG wire closely wound over a 5mm dia. air core
L2: 2 turns of 24 SWG wire closely wound over the 5mm dia. air core
L3: 7 turns of 24 SWG wire closely wound over a 4mm dia. air core
L4: 5 turns of 28 SWG wire on an intermediate-frequency transmitter (IFT) ferrite core
Check the related posts for some stereo fm transmitter circuits.
Monday, March 10, 2014
8 function christmas lamp
Description.
This 8 function serial Christmas lamp controller is based on the IC UTC 8156 from Unisonic. Specially designed for the same purpose, the UTC 8156 can control the four lamps in 8 modes namely waves, sequential, slo-gol, chasing/flash, slow fade, twinkle/flash, steady ON and auto scan. Control signals for controlling the lamps will be available at pin 12 to pin 15 of the IC. SCRs are used to drive the lamps according to these control signals.
Circuit diagram.
This 8 function serial Christmas lamp controller is based on the IC UTC 8156 from Unisonic. Specially designed for the same purpose, the UTC 8156 can control the four lamps in 8 modes namely waves, sequential, slo-gol, chasing/flash, slow fade, twinkle/flash, steady ON and auto scan. Control signals for controlling the lamps will be available at pin 12 to pin 15 of the IC. SCRs are used to drive the lamps according to these control signals.
Circuit diagram.
Notes.
- The circuit can be assembled on a Vero board.
- L1 to L4 can be 230V/40W lamps.
- H1 to H4 can be TYN612 SCRs.
- Heat sinks are recommended for the SCRs.
- IC1 must be mounted on a holder.
- If 1A bridge is not available, make one using four 1N4007 diodes.
- S1 can be an 8 through rotary type selector switch.
- S1 can be used to select the modes.
Multi-channel audio mixer circuit using LM3900
LM3900 multi-channel audio mixer.
A simple multi-channel audio mixer circuit using LM3900 quad amplifier is given below. The circuit consists of 4 channel quad amplifier (LM3900). Two mic audio inputs and two direct line inputs are available in this circuit. By adding the same circuit parallel with this, you can increase the number of inputs according to the applications. Each input is connected to the inverting terminal of LM3900.The built in amplifier of each section amplifies every audio input separately and is fed to the output terminals. The output terminal from each channel is connected to a single output line with a resistance not greater than 680K and produces a mixed audio at the output with very low noise. This audio mixer circuit doesn’t use a low impedance input to mix ideal sources. Capacitors C1 to C4 are the decoupling capacitors for the corresponding channels. C5 is the output decoupling capacitor.
Circuit Diagram.
Multi channel audio mixer circuit
General Description of LM3900.
LM3900 series amplifiers consist of four independent and internally compensated amplifiers that are designed for single and wide power supply voltage. These amplifiers provide a wide range of voltage inputs and very good response for all audio frequencies. They also provide a large output swing.
The architecture and pin configuration of LM3900 is shown in the picture below.
LM3900 pin configuration and architecture
The main features of this audio mixer circuit as compared to the other audio mixers are given below.
1) Wide range of supply voltage input (4volt to 32volt)
2) Dual voltage supplies also adoptable (+/- 2.2volt to +/-16volt)
3) Low input biasing current(30nA)
4) Providing very high open loop gain(70dB)
5) Output short circuit protection
6) Simple and compatible design
7) Low distortion
8) Good frequency response
Notes.
- Assemble the circuit on a good quality PCB.
- The circuit can be powered from anything between 5 to 30V DC.
- The power supply must be well regulated and free from any sort of noise.
- LM3900 must be mounted on a holder.
- VR1 to VR4 can be used for adjusting the volume level of the corresponding channels.
- All fixed resistors are 1/4 watt carbon film type.
- If the power supply circuit is far from the mixer circuit, then a 100uF/50V electrolytic capacitor must be connected from the positive supply rail to the ground.
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