CNC constant current source circuit diagram for battery charging

This picture is a numerically controlled constant current source designed to charge the battery. The D/A converter outputs a voltage value to the non-inverting terminal of the lower op amp. The current in the circuit is I=Uad/sampling resistor. The two PORTs are used to connect the + and - poles of the battery. The above operational amplifier is connected to an amplification circuit with an amplification factor of 1/4. Used to measure battery voltage. The two adjustment tubes in the picture are 3dd13 and 3dd15 respectively.