Some of the parts use +10V and -5V is the +10 a minimum value and +24V can be used instead?

No, read the according datasheet.

I have a few questions about the circuit.

1. The TLC352 LED illuminates when the common mode is at +3V or -3V?

No, if voltage at inverting input of INA128 is lower than -2.5V or when voltage at noninverting input is higher than +7.5V. This represents a common mode input voltage of +-2.5V.

Could that common mode out of range signal be a 5V logic signal that is compatible to an input into a microcontroller?

Yes, look at here:



2. You had mentioned that using a BJT transistor instead of a FET for the current limit would eliminate the use of a trimmer. Can you give some insight on how that would be accomplished using a BJT?

Have a look at above schematic. There you will find LM317T. By connecting it to 51R resistor, as shown, a very precise currrent limiter can be built. Maximum current is calculated by:

Imax = Uref / 51Ohm

As Uref is guaranteed between 1.20V and 1.30V (nominally 1.25V), set maximum current is between 23.5mA and 25.5mA (nominally 24.5mA). The advantage of this current limiter is, that there's nearly no temperature dependency. Also, drift is extremely small. This is direct consequence of highly stable Uref and extremely small error causing Iadj. With this design a calibrating of current limiting threshold is no longer necessary.

Disadvantage of this circuit is, that at 20mA about 2.5V are dropping across it: About 1.5V between input pin and output pin of LM317T and about 1V across 51R resistor.
Also, an additional transzorb is necessary, because LM317T does only tolerate input output voltages of 40V maximum.

Kai