Hi All,
Yet another question I'm afraid. I've made quite a few rfid readers now, using the u2270b for one type of transponder and the tms3705 for others.
This works ok but I have to use two coils, the tms has to come from the US and costs around £10 a time, blah blah blah!
My knowledge of rf electronics is limited, I've picked it up as I go along so maybe missing some basics! . Attached is a schematic of the basic building block for using the tms3705, a coil is attached to the conector forming a lc tank driven by the chip. Across the coil at the moment I am seeing 40v peak to peak, I have seen much more with different coils.
The data sheet states the maximum voltage at sense can be 0.3v above supply. The sense pin is the input to a rf amplifier, which is according to the data sheet a op amp with a fixed internal refrence, this feeds back to sense via sfb through a 150k resistor.
At sense which is 'across' the coil via a 47k resistor I am seeing about 5 volts peak to peak, my question is how can this happen? I would like use a op amp and comparators to replace the tms3705 but have a feeling there must be more than the rf amp attached to the sense pin inside?
Is there a op amp that could stick up to 180v peak to peak? (I've seen that much!)
Ps. this type of transponder charges then transmits when the field is turned off, it runs at 134khz
Cheers Geoff
Yet another question I'm afraid. I've made quite a few rfid readers now, using the u2270b for one type of transponder and the tms3705 for others.
This works ok but I have to use two coils, the tms has to come from the US and costs around £10 a time, blah blah blah!
My knowledge of rf electronics is limited, I've picked it up as I go along so maybe missing some basics! . Attached is a schematic of the basic building block for using the tms3705, a coil is attached to the conector forming a lc tank driven by the chip. Across the coil at the moment I am seeing 40v peak to peak, I have seen much more with different coils.
The data sheet states the maximum voltage at sense can be 0.3v above supply. The sense pin is the input to a rf amplifier, which is according to the data sheet a op amp with a fixed internal refrence, this feeds back to sense via sfb through a 150k resistor.
At sense which is 'across' the coil via a 47k resistor I am seeing about 5 volts peak to peak, my question is how can this happen? I would like use a op amp and comparators to replace the tms3705 but have a feeling there must be more than the rf amp attached to the sense pin inside?
Is there a op amp that could stick up to 180v peak to peak? (I've seen that much!)
Ps. this type of transponder charges then transmits when the field is turned off, it runs at 134khz
Cheers Geoff