Boxing an Arduino ADF4351 Signal Generator

After reading a Radcom article about a 10MHz locked ADF4351 Arduino controlled  signal generator thanks to Alain Fort F1CJN described here,  it seemed the perfect module for testing equipment locally as I didn’t have anything like this.

Once the pieces arrived from China it worked perfectly with a 10MHz GPSDO input using the instructions from Alain’s page above and the black ADF4351 board after disconnecting the on-board 25MHz clock.

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When connected, the above worked fine and did okay on the desktop it wasn’t suitable for moving about or with the jumper cables for long term storage/use. A box was ordered large enough to place all of the bits in and to allow SMA & DC inputs as well as another shield that didn’t have the headers I’d put on the above one.

The Arduino LCD/Button shield works well but doesn’t lend itself at all well to being installed in a box. The LCD brightness adjustment capacitor is too big, there’s some header pins sticking up to the LCD level and the buttons are too far recessed for access through a box. Some discussion on the ukmicrowaves mailing list gave some pointers for getting around these problems.

Firstly the buttons were all removed and the variable capacitor was moved to the other side of the PCB.

JtlFAby I wasn’t sure of the size of buttons to replace the originals with to allow them to be pressed when mounted in the case so I had also ordered a mixed pack on eBay to allow picking the appropriate size. I also ordered some white caps for the tops which would eventually be glued on. I eventually settled on the combination lush with the LCD.

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Now came the part I wasn’t looking forward to, drilling and cutting the case. The LCD shape along with the four mounting holes was drawn out based on measurements from the board and cut. I don’t have any nice tools for the LCD rectangle cut so cut two sides with with a hand hobby saw and others with a rotary tool to compare the finish as wasn’t sure of the best approach. The rotary tool was fast but gave a terrible finish, the hobby saw plus sanding gave by far the better result.

The more tricky bit was the button measurements and I couldn’t find a PCB diagram for the board. Putting some fabric tape on the inside of the case and ink on the top of some temporary placed buttons I pushed the LCD in to it’s fitting which after a couple of goes left an imprint on the inside.

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This allowed me to drill an initial hole from the inside before turning over to drill an appropriate sized hole from the other side.

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Once I had validated the holes were lined up, they were expanded to fit the white caps using a drill and a deburring tool. I then checked the button lengths for the best match, soldered the buttons to the board and glued the white button caps to them.

Three holes were drilled in the side for two SMA and a DC input and some stickers added to make it look better by hiding the messy top cut made by my bad effort with the rotary tool…

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The inside has the LCD shield and Arduino attached to the lid using machine screws and some spacers to hold things in place. The Arduino needed it’s DC socket removed to fit flush with the LCD shield. Wires were soldered directly in to the Arduino for the output to the resistor divider and DC input.

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In the picture above the DC input is going to the Arduino DC input. However the regulator in the cheap Arduino Uno copy I’d obtained from eBay turned out not to work with a 12v input in the same way as the genuine Uno I tested with had. To sort this I skipped the regulator by putting a small buck converter in the case to let it regulate the voltage to 5v and connected it directly to the 5v on the Arduino.  As well as solving the problem, the converter gives better a 6-20v input range.

Another thing I should have done was used a right angle SMA connector for the ADF4351 output as the cable bend’s a bit tight. The whole thing could do with some better internal placements, for instance the shorter coax run being the 10MHz input instead of the higher output but it worked out okay in the end!

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This is the first time I’ve boxed a project like this and I’ve learned a few things along the way. I now have a wish list of a 3D printer, drill press, CNC machine and a laser cutter… Any pointers on doing this better/easier without better tooling would be greatly appreciated 🙂

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