Hi all,
I've recently started fiddling in the murky world of analogue signals and op amps, as usual I started fiddling with out any more than a rough idea what was going on. After a lot of googling and poking stuff with a scope (pc picoscope, if you need a scope and haven't got one I'd recommend it!) I now have the bare bones of a rfid reader. I've yet to program a pic to decode the signal but have it 'extracted' from the carrier.
This brings me to my questions, firstly I'm using tl082 op amps (because their cheap and it was what other folks have used) I've an idea they might not be exactly the best for my application though, I read on this forum they are only spec'd to get within three volts of the rails, I have gnd, 12v and 5v at the moment, 12v runs a mosfet driver ic, 5v logic which controls the driver. I could use comparators on the pic and a protection diode to read the signal but think a rail to rail op amp would be best.
This is a long winded way of asking if anyone has a favourite rail to rail op amp?
I also read somewhere that for a active bandpass filter you should have 100x bandwidth op amp, is this right? The tl082 is 3MHz my signal is 134kHz and it works?! Have I just been lucky.
The carrier wave is also quite big, I've put clamp diodes on the first op amp to stop it getting cooked, are there any op amps that will stick around 20x supply at the inputs?
Last thing (maybe!) one of the op amps is working as a comparator, I read on one web page this isn't a good idea? I like it because it cuts down on the number of different chips I need but would I be better off with a dedicated comparator?
So basically I'm looking for a cheap rail to rail (12v-15v) op amp that can stick high inputs and work reliably as a comparator. There seems so many to choose from and I know there is a lot of experience on this site.
Cheers Geoff
I've recently started fiddling in the murky world of analogue signals and op amps, as usual I started fiddling with out any more than a rough idea what was going on. After a lot of googling and poking stuff with a scope (pc picoscope, if you need a scope and haven't got one I'd recommend it!) I now have the bare bones of a rfid reader. I've yet to program a pic to decode the signal but have it 'extracted' from the carrier.
This brings me to my questions, firstly I'm using tl082 op amps (because their cheap and it was what other folks have used) I've an idea they might not be exactly the best for my application though, I read on this forum they are only spec'd to get within three volts of the rails, I have gnd, 12v and 5v at the moment, 12v runs a mosfet driver ic, 5v logic which controls the driver. I could use comparators on the pic and a protection diode to read the signal but think a rail to rail op amp would be best.
This is a long winded way of asking if anyone has a favourite rail to rail op amp?
I also read somewhere that for a active bandpass filter you should have 100x bandwidth op amp, is this right? The tl082 is 3MHz my signal is 134kHz and it works?! Have I just been lucky.
The carrier wave is also quite big, I've put clamp diodes on the first op amp to stop it getting cooked, are there any op amps that will stick around 20x supply at the inputs?
Last thing (maybe!) one of the op amps is working as a comparator, I read on one web page this isn't a good idea? I like it because it cuts down on the number of different chips I need but would I be better off with a dedicated comparator?
So basically I'm looking for a cheap rail to rail (12v-15v) op amp that can stick high inputs and work reliably as a comparator. There seems so many to choose from and I know there is a lot of experience on this site.
Cheers Geoff