Programmable attenuator using HP8494G (11dB) and HP8495G (70dB). Both stepped attenuators are controlled using Atmega168 (328) uC and ULN2003 coil driver. Attenuation value is displayed by 2 digits LED commun cathode or commun anode.
Attenuation is adjusted between 0dB...81dB by 1dB step. Input power must to be less than 1W (30dBm), DC component max. +/-7Vdc or better avoid DC input, up to 4GHz. Insertion loss during bypass is 0.3dB/145MHz and 0.8dB/1.5GHz.
The attenuator can be bypassed by pushing encoder button, "00" flashing will be displayed. Last value is stored inside of EEPROM.

Update 11.2021: firmware v1.2 provided to fix chineese rotary encoder instability. Also debounce capacitors installation is required (issue reported by F5SUE, tnx).

Atmega Controller Schematic v1.2
PCB
Firmware Hex v1.1 - unknown TOCOS quadrature rotary encoder tested
Firmware Hex v1.2 - Chineese quadrature rotary encoder tested
Fuse Bits internal 8MHz: eXtreme Burner or TL866II-Plus
HP849x Datasheet
Inside view
Visuino project v1.2 - can be open by Visuino software

yo4hfu@2010-2021