125kHz transmitter design

[fedimakni]

Hello,

My target is to build a 125kHz transmitter. As you can see in the picture below this is a schematic for a 125kHz transmitter from sciosense. I didn't understand well how it works (transmission side) but i think that they are  controling the gate of the mosfet and switch it on/off to send the data.
I would like to understand more how it works in term of hardware and especially in the software side. What's the logic behind the state of the mosfet to send specific data?
Are there document which provide informations about that?
Any open hardware/software project about it?
I prefer to use the same schematic but just by changing the microcontroller to another one but if there are other suggestions i will be very thankful.

Thanks

[NiHaoMike]

It looks like they're using a phase shift PWM topology with a series resonant antenna circuit.

[T3sl4co1l]

Well, software side is whatever it's doing there, you'll have to look that up.  Hardware is just an H-bridge driving a series resonant tank, or so it appears.  Power level can be controlled by phase shift between sides, or duty cycle; so that gets AM, ASK, etc., and by varying timing, phase or frequency modulation (PSK, FSK, etc.).

And, for... whatever it's for.  If it's like RFID tags then that'll be ASK, and, Idunno what else, there's no receiving on that circuit...

Tim

[fedimakni]

@NiHaoMike
Yes i think that's correct, but what about the software side, i think it's the most important right?

[fedimakni]

@T3sl4co1l
Thanks for the reply,
depending on what i saw in the datasheet it's not RFID
they also use manchester encoded in their product description, but what about the software there's no document which can explain similar thing?
Also what's AM ASK? Thanks
 

[T3sl4co1l]

AM, amplitude modulation. Varying the pulse width or phase shift varies the square-wave area driven into the load, and thus the amplitude of the 125kHz component (fundamental).  Harmonics can be mostly ignored due to the filtering effect of the resonant load.  ASK is the special case where the amplitude is shifted between levels (amplitude shift keying).  As opposed to full on-off (like old school Morse code keying).  Similarly, PSK and FSK are digital modes but shifting phase or frequency between two states.

I don't think you'd use Manchester to drive the coil directly, but that can be used on the signal, applying whatever modulation scheme after.

Tim

[David_1]

is this a Transmitter or a reader ? for door entry / dog tags ?