Digital gain control of Opamp
The gain of U1 can be controlled by a digital binary 1248 nibble at ABC. The gain at digital 000 is unity or 1 and the gain at various stages are set by 4051.The on resistance of 4051 channel around 100E gets added to U1 pin 2 internal impedance.
You can use separate resistor networks with trimpots for each channel if you require
but keep the networks total burden on U1 pin 6 to around 10K, not less than than.
You can use this to set the gain of a amplifier with the help of a microcontroller.
