Cut the traces shown above. Cutting the trace on the USB adapter PCB isn’t necessary, but it prevents your computer from powering the module if the module has no power from the rack.The cuts are easily done with a sharp razor. Scrape away the green solder mask over a small part of the trace so you can see the copper clearly. Then scrape away the copper. Check the continuity between the trace to make sure it’s cut.Optionally, put a dab of nail polish over the cut to protect it.
Mount parts in this order:
SMD components (resistors, diodes, ICs)
There’s caps on the bottom of the PCB too.
Double-check the IC orientations. The opamp is pointing down.
Check the “CONFIGURING OUTPUT” section below for opamp jumper/resistor positions.
Note that the Opamp silkscreen reads “TL072”, meaning a typical 8-pin dual opamp. While a TL072 works fine, a “precision opamp” like a TL052 or OPA2277 should, in combination with a precision voltage reference like the ADR5041B, will ensure 1V/Oct tuning is accurate to under 1 cent. Tuning with the TL072 is accurate to within a few cents (ie: still in tune).
This is awkward because the female header for the Nano overlaps the pots on the opposite side.
The expansion header should be a 90 degree header — NOT like the one shown in the pictures. It can be left out for now.
Be careful not to burn the Nano header.
Depending on the type of pots, you may have to trim some of the Nano header pins.
Some pots may require the front support next to the legs to be bent upwards so it doesn’t touch the Nano header pins.
Jacks and LEDs
Use the panel to temporarily hold everything in place for soldering.
The voltage reference and opamp outputs are configurable with either SMD or through-hole parts. This is designed for maximum configurability when testing parts. Leave the “VREF” area labelled below empty, and put a wire or 0-ohm resistor across GAIN shown below.It’s possible to configure for bipolar and stretched outputs, but hasn’t been tested thoroughly yet.The PCB should look something like the pictures below:
Assembling USB Connector
The connectors are overlapping on both sides of the PCB, so is a little awkward to put together.
Dry-fit the parts to make sure they fit. There will probably be a little leg-bending to get it to fit. There are a lot of parts that look similar but have slightly different hole/pin positions. The Digikey parts listed in the BOM fit best (but still require a bit ofleg-bending), but other parts could also work — or not.
Solder the big square USB B connector first. It has pins that will end up under the USB A connector. It may be necessary to trim the end of the pins flush to the board.
Solder the rectangular USB A connector. Its pins should come out just above the B connector. Don’t use too much solder, and trim the leads flush to the PCB. I put a bit of hot glue stick here also.
It’s attached with a couple m3x6 bolts and three nuts per bolt. One nut tightens the bolt to the panel, another keeps the USB adapter PCB from going in too far, and the final nut tightens the PCB against the second nut.Alternatively, If the sides of the adapter PCB are filed/ground down a bit, the USB fittings can be installed upside-down.A panel-mount USB cable like this one from Adafruit will also work, but may not fit into some cases without trimming away some of the plastic.
Remove Nano if installed.
Test for shorts through power connector (RED on diagram below).
If there’s a short check all solder connections before continuing.
Plug in power cable and check for +12 and -12 Voltages at the YELLOW points shown below.
Without a load the voltage may be as high/low as +/-17V.
Turn off power, and install Nano.
Check for 5V and 2.5V at the test points labelled on PCB.
5V can be +/- .2V
2.5V should be +/- .01V (2.49V – 2.51V) or less. The voltage reference may be more accurate than your multimeter so don’t worry if your multimeter shows it off by a millivolt or so.
Putting it all together
Mount the PCBs to the panel, and attach the USB cable to the Nano. You should now be able to load sketches through the front panel.Sketches are loaded with the stock Arduino IDE. Sketches ready to go can be found here.