Controller Attenuator Agilent/Keysight 8494H & 8496H

Greetings!

It so happened that we got two attenuators Agilent 8494H and 8496H. They were lying idle for a long time, because there was no control controller. Of course, four simple switches would cope with this task, but I wanted an implementation with a display showing the current attenuation value and software control. The project was made in Altium Designer and Atmel Studio.

Supplies

attenuators Agilent/Keysight 8494H & 8496H
atmega328-AU
address latch SN74HC259
transistors Darlington ULN2803
virtual COM port CH340G
DC-DC step-up circuit XL6009
DB-9, USB type B, headers
encoder

Step 1: Circuit & PCB

The controller is built on the Atmega328-AU placed on a double-sided printed circuit board. The circuit is powered from the USB port (5 V). To switch the solenoids in the attenuator, a voltage of 24 V is required, which is obtained from the DC-DC step-up circuit (5 V - 24 V). This voltage is supplied for a very short time, about 50 ms.

The encoder is used to increase and decrease the attenuation, the encoder button is used to select the attenuator.

Step 2: Decoder Logic

To control the attenuators, a binary code (from 0 to 7) is fed from the microcontroller to three inputs of the SN74HC259 address latch; then eight outputs are connected to ULN2803 Darlington transistors, which pull the ground to the corresponding wire.

Step 3: Cable Soldering

Soldering the cable to the DB-9 connector. There are 9 wires in the cable, 24 V is supplied to the red one, and ground is supplied to the rest, depending on the position of the attenuator.