Upgraded 555 timer based AM transmiter pt.2

Schematic of TLC555 timer based AM transmitter. It is really not much more than the 555 setup in astable mode. Be sure to use the TLC555 version of the timer chip. If you're in the US, it can be found at Radio Shack stores.

Category:

Science & Technology

Tags:

• 555am2

[sangjago]

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?

[vegmatic1966]

@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]

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...

[vegmatic1966]

@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]

Any alternatives to a 330 pf cap, cant find one ANYWHERE

[vegmatic1966]

@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]

@uN1Qu3DZ How did DC get through? The capacitor is there to block the DC.

[Mrnitrocker]

@dvdragond2 : Bro its a TLC555CP....

bt either wont matter....

as long as it is frm d TLC555 series

[Mrnitrocker]

@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

[dvdragond2]

which version of the TLC555 timer was it? TLC555CP or the TLC555IP. and if they aren't the ones then im out of luck

[dasraiser]

@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.

[CassetteMaster]

I just built this and it works very nicely! It is awesome, and interesting to use a 555 as a transmitter.

[BurningSandman]

@vegmatic1966 Thanks, I got it working great! Now to make a rf amp...