The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 11
Figure 11-3. An LF13006/7 controls the gain of an LF411 op amp.
The bits that select the gain are outputs of a 74LS374 latch addressed at E400h. The
LF13006/7’s Chip-Select and Write pins are tied low, which causes the gains at pins 12 and
6 to immediately match the settings at DIGIN1-DIGIN3.
If you want to control up to four gain-set chips and op amps, you can use the five remaining
outputs of the 74LS374 to select the desired chip. Tie all of the WR inputs to one bit, and tie
each CS input to one of the remaining bits. Then, to set the gain of an op amp, bring its CS
input low, then bring WR low, then high to latch the data to the desired chip.
You can use just about any op amp with this circuit. Shown is an LF411, which has a wide
bandwidth and low input offset and drift. A 10-picofarad capacitor from the op amp’s input
190 The Microcontroller Idea Book