@sangjago Astable is a free running oscillator, so yes, it has to be. Varying voltage on pin 5 changes the trigger point which shifts the pulse. The duty cycle changes and this modulates the carrier with the audio content. See 555 datasheet "pulse position" modulator diagram. This is where I got the idea.
@Mrnitrocker Finding the impedance on pin 5 inside the chip would allow one to calculate the corner frequency using that capacitor. You might be right that it can use a larger cap, but just sticking a larger one in would not make sense without calculations first.
@BurningSandman Check the 555 data sheet and select the combination of capacitance and resistance needed to operate at the desired carrier frequency. There are charts to make it easier. Good luck.
@MrDanishilyas maybe, if you use 4xNE555 and cascade trigger on quarter cycles with duty cycle of 12.5%, so if im correct at 250KHz you get 4 on/off pulses giving 1MHz at 50% duty cycle.
What value is the variable capacitor? What range do you get from what length of antenna? You say the coil is an AM loopstick, you mean ferrite bar as typically found in transistor radios? If so, what leads connect on the loopstick? Thanks much.
@3mustardMoNkEyS Yes, that pretty much sum it up. Many transmitters operate in class C mode and the active device output is pretty distorted. The tuned circuits clean it up nicely into a nearly perfect sine wave (low harmonics).
i couldn't get the dual 555 circuit working properly no matter what. i decided to use the 555 as carrier generator only and have a 2N3904 as the modulator and mixer. i now get some ultra high quality radio silence :)
i'll have to play a bit more with the coil in the collector of the transistor, i think it's too small, coz it distorts at a quite low level of modulation. but other than that it sounds okay, it's a lot cleaner than the single 555.
oh and to everybody building this - ADD A 10K RESISTOR TO GROUND AFTER THE INPUT CAPACITOR or you will get DC voltage thru to the input device. sorry for shouting but i blew my PDA's output coupling caps AGAIN. i just fixed the damn thing last month.
for me it's an easy fix since i know what's involved, but for a newbie finding that your music player now heats up your headphones instead of playing music can be a bit confusing and disheartening. so put that resistor in there okay?
@vegmatic1966 it's simple really. DC will get through the cap if there is infinite resistance between the other side of the cap and ground. well technically not really DC but a ramp down with a loooooooong time constant, enough to cause trouble.
it only happens when you connect two capacitor coupled devices to one another. if your signal source has an internal resistor between output and ground after the coupling cap, or if your source is DC coupled then the DC is blocked by the input cap in your circuit, but if the circuits are both capacitor coupled with no resistor to ground between the two caps, the bias of the control pin, about 5v, will flow through both caps and damage the caps of the source if their voltage rating is low enough.
the main reason behind the harmonics is that the 555 does PWM and PFM at the same time - frequency and duty cycle are interlinked and both change when a signal is input.
the more elegant version would use two 555s (or one 556).
is this timer operating in astable mode? and also why did you put the audio source into pin 5? what does the control voltage pin do?
sangjago 3 weeks ago
@sangjago Astable is a free running oscillator, so yes, it has to be. Varying voltage on pin 5 changes the trigger point which shifts the pulse. The duty cycle changes and this modulates the carrier with the audio content. See 555 datasheet "pulse position" modulator diagram. This is where I got the idea.
vegmatic1966 2 weeks ago
Why do v use a 0.22 uF Capacitor at the audio input side ???
y nt a larger value of capacitor???
the audio signal will pass thru even more smoothly wid lower resistance!!
pls guide...
Mrnitrocker 3 weeks ago
@Mrnitrocker Finding the impedance on pin 5 inside the chip would allow one to calculate the corner frequency using that capacitor. You might be right that it can use a larger cap, but just sticking a larger one in would not make sense without calculations first.
vegmatic1966 3 weeks ago
@vegmatic1966 : also sir the video part-1 demonstrated a broadcast with a tape recorder there u had a audio jack connected to the tape....
frm that jack there were 3 sets of outgoing wires...
hw is one suppose 2 recognize which goes where...
kindly explain n elaborate
Mrnitrocker 3 weeks ago
which version of the TLC555 timer was it? TLC555CP or the TLC555IP. and if they aren't the ones then im out of luck
dvdragond2 2 months ago
@dvdragond2 : Bro its a TLC555CP....
bt either wont matter....
as long as it is frm d TLC555 series
Mrnitrocker 3 weeks ago
I just built this and it works very nicely! It is awesome, and interesting to use a 555 as a transmitter.
CassetteMaster 10 months ago
Any alternatives to a 330 pf cap, cant find one ANYWHERE
BurningSandman 11 months ago
@BurningSandman Check the 555 data sheet and select the combination of capacitance and resistance needed to operate at the desired carrier frequency. There are charts to make it easier. Good luck.
vegmatic1966 11 months ago
@vegmatic1966 Thanks, I got it working great! Now to make a rf amp...
BurningSandman 11 months ago
Hi whats the best range you have had with this circuit?
miked351 1 year ago
would it still work with NE555 timer? Any further modifications required for that?
MrDanishilyas 1 year ago
@MrDanishilyas maybe, if you use 4xNE555 and cascade trigger on quarter cycles with duty cycle of 12.5%, so if im correct at 250KHz you get 4 on/off pulses giving 1MHz at 50% duty cycle.
dasraiser 6 months ago
What value is the variable capacitor? What range do you get from what length of antenna? You say the coil is an AM loopstick, you mean ferrite bar as typically found in transistor radios? If so, what leads connect on the loopstick? Thanks much.
gandsnut 1 year ago
@gandsnut The blue / back wire and the uncolored wire
miked351 1 year ago
So the Tuned Cap and Loopstick are acting as passive filters to prevent any harmonics to be transmitted?
3mustardMoNkEyS 1 year ago
@3mustardMoNkEyS Yes, that pretty much sum it up. Many transmitters operate in class C mode and the active device output is pretty distorted. The tuned circuits clean it up nicely into a nearly perfect sine wave (low harmonics).
vegmatic1966 1 year ago
i cant see ground on this
dodgedart74 1 year ago
@dodgedart74 pin 1 is ground
miked351 1 year ago
okay... sorry. I see you put it in part 2. Thanks /John
bearing01 1 year ago
i couldn't get the dual 555 circuit working properly no matter what. i decided to use the 555 as carrier generator only and have a 2N3904 as the modulator and mixer. i now get some ultra high quality radio silence :)
i'll have to play a bit more with the coil in the collector of the transistor, i think it's too small, coz it distorts at a quite low level of modulation. but other than that it sounds okay, it's a lot cleaner than the single 555.
uN1Qu3DZ 1 year ago
sorry for double posting, internet acting up. atm the PCB for the dual 555 version is etching. i'll post a video of mine in a couple days.
uN1Qu3DZ 1 year ago
oh and to everybody building this - ADD A 10K RESISTOR TO GROUND AFTER THE INPUT CAPACITOR or you will get DC voltage thru to the input device. sorry for shouting but i blew my PDA's output coupling caps AGAIN. i just fixed the damn thing last month.
for me it's an easy fix since i know what's involved, but for a newbie finding that your music player now heats up your headphones instead of playing music can be a bit confusing and disheartening. so put that resistor in there okay?
uN1Qu3DZ 1 year ago
@uN1Qu3DZ How did DC get through? The capacitor is there to block the DC.
vegmatic1966 1 year ago 3
@vegmatic1966 it's simple really. DC will get through the cap if there is infinite resistance between the other side of the cap and ground. well technically not really DC but a ramp down with a loooooooong time constant, enough to cause trouble.
uN1Qu3DZ 1 year ago
it only happens when you connect two capacitor coupled devices to one another. if your signal source has an internal resistor between output and ground after the coupling cap, or if your source is DC coupled then the DC is blocked by the input cap in your circuit, but if the circuits are both capacitor coupled with no resistor to ground between the two caps, the bias of the control pin, about 5v, will flow through both caps and damage the caps of the source if their voltage rating is low enough.
uN1Qu3DZ 1 year ago
the main reason behind the harmonics is that the 555 does PWM and PFM at the same time - frequency and duty cycle are interlinked and both change when a signal is input.
the more elegant version would use two 555s (or one 556).
uN1Qu3DZ 1 year ago
I really love the design, how would you design the Loopstick antenna?
303nx 1 year ago