A DIY bench RF step attenuator with Arduino and Aeroflex-Weinschel step attenuators

A while ago I made a bargain purchasing a couple of Aeroflex-Weinschel step attenuators (models 150T/11 and 150T/70) for 20EUR each.

The idea was to implement a bench step attenuator for my lab.

Here is the project.

Those attenuators offer serial and parallel digital interface. I choose to use the parallel interface protocol.

Each attenuator is controlled by 4 bits (a nibble), so, with the help of the following map, I built an Arduino sketch to drive the attenuators by a rotary encoder:

The table on the left simply lists all the wires coming out of the attenuators with color and function.
The two tables on the right show the parallel protocol details for the 150T/11 and the 150T/70 respectively: what attenuator setting corresponds to which nibble value. They also show the Arduino micro<->attenuator physical interface (what Arduino's pin goes to which attenuator wire).

The attenuators were cascaded by mean of SMA to SMA RF rigid cable; the input and the output were brought to the front panel by mean of a couple of SMA to N Bulkhead rigid cables.
If it has been built following all RF precautions, the final product would be capable of reaching a DC-18GHx bandwidth. I suppose my implementation should be able to reach a couple of GHz, ...far beyond my actual lab upper limit.

The rotary encoder has been programmed to step the attenuators up and down. Pressing the knob, toggles between 10dB and 1dB steps.

If you want more details I suggest you to have a look at the Arduino sketch that contains a lot of comments. Despite making every effort to correct the problem, the encoder occasionally misses a beat.

The enclosure has been recovered from a previous project and the front panel layout has been designed using Kicad:

The 7 segment display has been recovered from an old industrial control board.

The switching power supply used in this project has been recovered form a faulty LAN switch. It provides the necessary 12V and 5V rails.

Here is the final product:

Have a look at it, live, during testing...

I had fun, I spent few bucks, I eventually have a bench step attenuator form my lab.

Hope this content can help other makers..

Ciao.