Use this circuit as a low cost alternative to a commercial DAC.
It is important that the latch be a CMOS device, so that the outputs drive to Vcc
when they are high. (TTL devices only drive to 2.4 volts or so).
I have shown the '573 latch rather than the '373 which can also be used. The '573 has the advantage of sequential pin-outs for the Q0 - Q7 pins, making it easier to connect in most circuit layouts.
The LM358 OpAmp is a good choice for this circuit for two reasons: 1) It can be powered from the 5V supply. 2) Its output can go to 0V without a negative power supply. Note that the LM358 is a dual OpAmp, so the other half is unused in this circuit.