circuit design question
So i'm in the process of converting a voltage controlled device into a current controlled device which utilizes the PIC16C54C microcontroller. The original voltage controlled schematic involved using multiple ZVN3306FCT-ND MOSFET transistors which were controlled by the PIC. These MOSFETs had resistors connected, in parallel, so by controlling various MOSETS, we could output a thevenin equivalent voltage from another voltage and resistor combination.
Instead of being able to control this voltage, i'd like to be able to control the current. Any ideas would be appreciated. I've attached a picture of the design itself, highlighting the MOSFET transistors.