Hello.
I'm trying to build a hakko 907 (24V 50W) controller, but I don't have much experience with op amps, and I have concerns about the circuit I came up with. Here it is: http://i.imgur.com/ZalB8RG.png
It consists of Wheatstone bridge and a single rail differential amplifier with a gain of 3.6. The 220 Ohm resistor was chosen with assumption that the resistance won't go over 220 Ohms, based on some of the charts I found online. The gain was chosen so that the output voltage don't go near the positive rail, and 3.6V can be divided into ~720 steps with 10 bit ADC, which is more than enough.
The choice of op amps in the local shops is pretty scarce, and I wasn't able to find any rail to rail op amps, just the common ones like UA741, LM324 and LM358. Could probably order them from china, but then I'd have to wait for a few months, so I'm keeping that as a last resort, in case I can't use the available ones.
So, my concerns now:
I wasn't able to find a tutorial written by a "professional" that uses a differential amplifier in single rail mode without voltage splitter circuit, and yet I found some people use it like that (example). Is this a bad way to go, and if yes, why?
Also, I am not really good at reading op amp datasheets. If I understood correctly, the output voltage quality will start to deteriorate with lower difference at the input, as it approaches the negative rail. Where in the datasheet should I look to find out at what voltage should I expect that to happen? If this is correct of course.
Thanks in advance ,
Miloš
I'm trying to build a hakko 907 (24V 50W) controller, but I don't have much experience with op amps, and I have concerns about the circuit I came up with. Here it is: http://i.imgur.com/ZalB8RG.png
It consists of Wheatstone bridge and a single rail differential amplifier with a gain of 3.6. The 220 Ohm resistor was chosen with assumption that the resistance won't go over 220 Ohms, based on some of the charts I found online. The gain was chosen so that the output voltage don't go near the positive rail, and 3.6V can be divided into ~720 steps with 10 bit ADC, which is more than enough.
The choice of op amps in the local shops is pretty scarce, and I wasn't able to find any rail to rail op amps, just the common ones like UA741, LM324 and LM358. Could probably order them from china, but then I'd have to wait for a few months, so I'm keeping that as a last resort, in case I can't use the available ones.
So, my concerns now:
I wasn't able to find a tutorial written by a "professional" that uses a differential amplifier in single rail mode without voltage splitter circuit, and yet I found some people use it like that (example). Is this a bad way to go, and if yes, why?
Also, I am not really good at reading op amp datasheets. If I understood correctly, the output voltage quality will start to deteriorate with lower difference at the input, as it approaches the negative rail. Where in the datasheet should I look to find out at what voltage should I expect that to happen? If this is correct of course.
Thanks in advance ,
Miloš