Constant Current sensor adjustment w/ LM317

[MrDEB]

Need to compare the sensor output (junction of R1/R5) using ADC on RA0 with desired temperature setting using 5K pot which will vary the output voltage at junction of R2/R8.
Contemplated using an op amp but then why bother using a PIC. Besides the end result would not what I am after.
Unless someone has a better solution.
The LM317 constant current source is perhaps the best solution for the sensor which is a thermistor HAKKO 907 iron sensor which has a resistance of 50ohms RT and 180ohms at solder melt..
I know this seems kinda convoluted but ??

 

[ericgibbs]

hi deb,
Look at using a LM393 dual comparator to compare the Tref and Tsensor

 

[MrDEB]

THANKS Eric BUT
I am wanting to have the LCD display DESIRED TEMPERATURE (RA1) and ACTUAL TEMPERATURE (RA0).
Looks like using the LM393 I only get one output, not two (DESIRED & ACTUAL) plus I find using a simulation (TINA as well as LTSpice the first resistor in the divider dosn't makemuch diffference with a CCS feeding the voltage (R1/R5 and R2/R8)divider
hope this makes sense.
Was contemplating using an LM324 op amp set up as a Howland grounded load constant current source. Problem is the circuits I found were duel supply. Did find one that was single supply but the schematic doesn't jive with the caculations.https://michaelgellis.tripod.com/howland.html
tried different values for R1 but both resistors marked R1 can't be the same. Simulation goes a negative voltage. Unless the PIC ADC can accept a negative voltage?