@SiliconWizard
There is a PDF of a schematic in the folder \JBC-Soldering-Controller-master\Hardware called JBC-Soldering-Controller_SCH_[No Variations]
OK - missed it because the whole file name was truncated so I had assumed it to be an Altium file or something. Just took a look, and realized that I've seen this schematic on another web site actually. Didn't remember it was this same guy. So yes, as you can see, he uses an high-side power switch and an ADS1118 for TC measurement. I use an ADS1115, mainly because it's I2C and I have a few I2C ICs in my design, so that was handy. I can use a 48-pin µC (with only 2 IOs left). The 1118 has an integrated temperature sensor, which the 1115 doesn't have. But I use a separate temp sensor (Si7051).
Whether you use a front-end amplifier or not, don't forget to add the protection you've probably seen in several schematics: the series resistor with 2 diodes. Because when the heater is ON, this can see 24V. In this guy's design, the series resistor is only 470 ohm and there are no external diodes. I don't think this is proper protection. The internal pad diodes of the ADS1118 will clamp it to Vcc+Vf at a current of approx 50 mA, which may destroy them in the long run. And I'm not talking about kick-back due to the inductive characteristic of the heaters. Ouch. In most controllers I've seen, a series resistor of 5k to 10k is used followed by two diodes to ground in opposite direction.
If I am using DC to run the tip/s I should be able to limit the current with the LM317 in current regulation mode ?
Yes, or any hardware current limiting option. You could do this in software only, but as I gathered, you may not be confident enough in your software skills to do this safely (and there are always possibilities of bugs).
One thing to consider is that to get the most of those tips, you'd ideally have to implement a current limitation that's different for the short or long-term. Allowed peak power for fast heating is at least twice what is recommended for continuous power delivery.