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.

1. attenuators Agilent/Keysight 8494H & 8496H
2. atmega328-AU
3. address latch SN74HC259
4. transistors Darlington ULN2803
5. virtual COM port CH340G
6. DC-DC step-up circuit XL6009
7. DB-9, USB type B, headers
8. encoder

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.

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.

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.

Since the device is used to automate measurements, it has software control via a virtual COM port.

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