Daisy-Chain Voltmeter Clock

This is my build of the Wicked Device Angular Clock, an Arduino-based PCB which drives three voltmeters to display hours, minutes, and seconds. It uses the square “quadrant” style of panel meter, and each meter is in its own case, daisy-chained together with TRS cable.

The printable parts are provided as STLs, as well as the original models for the cases and mounting bracket (SketchUp) and knob (OpenSCAD). The dials are provided in Illustrator and PDF, and use the DIN typeface (open source version here).

Parts required

• Angular Clock, board only (not the kit)
• Square 3" panel meters. This model is designed specifically to accommodate this one, though you may be able to use others. If you can't find a 5V meter, you can likely get a higher-voltage meter and change the resistors in them to a lower value. I used 3.3k resistors which provides full needle deflection around 3V (the voltage sent to the meters can be calibrated in software).
• IDC 2x3 pin ribbon cable
• Two 3.5mm TRS (stereo) jacks
• 3.5mm TRS (stereo) patch cable (I like this one because the connectors are very compact and the cable cross-section is round)
• Micro-USB cable + 5VDC power source (old phone charger works well for this)
• Soldering equipment, wire strippers, shrink tubing/electrical tape, drill, optional silicone sealant
• Optional CR1220 battery for maintaining time during power loss

Build instructions

1. Print the parts

• Case for hours, minutes, and seconds; setting knob; and mounting bracket for PCB. The parts can be printed without supports (except the mounting bracket), with the case backs face down. The holes for the two small screws will need to be carved out with a small screwdriver or knife (a solid layer was included to allow for a countersink with no need for supports).

2. Modify the meters

• Take out the two small screws at the rear of the meter, remove the rear black section (disconnecting the internal wires), and discard it.
• Take out the four screws in the corners of the white section and remove it. The meter mechanism and dial will come out with it. Print and install the replacement dial, then reinstall the mechanism, making sure the peg on the front adjustment screw fits into the slot on the front of the mechanism.
  • Alternatively, use flat-bladed screwdrivers to release the eight clips around the edge of the front bezel (two per side), pop it off and remove the glass. This method is a bit fussier, but also allows you to clean the inside of the glass while replacing the dial.
• Drill a second hole in the mechanism housing for the positive wire on the hour and minute meters, as shown. This is because the TRS jack will sit right over the old hole. Ensure no plastic shavings are loose inside the mechanism housing. I removed the mechanism from the housing (from the front) for this step.
  • Alternatively, modify the model to move the hole for the TRS jack; but I like it where it is.

3. The hours unit

• Install the mounting bracket on the bottom side of the PCB, and use soldering iron to melt the standoffs in the corners, to hold it in place.
• Install ribbon cable on the meter pins as shown, and identify the wires (from the knob side, it should go seconds/ground, minutes/ground, and hours/ground). Both minutes/seconds will be grounded through one wire, so you can trim off the other as shown.
• Loosely connect the hour meter and test it. As mentioned above, you may need to replace the resistor on the positive side of the meter with a lower-value one to get full deflection, especially if your meter is >5V. When it tests well, add shrink tubing and solder it together.
• Solder the three remaining wires to a TRS jack: seconds to tip, minutes to ring, and ground to sleeve.
• Insert all the components into the rear of the meter. The TRS jack I spec'd doesn't have threads, so use silicone sealant to adhere it to the back of the mechanism housing as shown.
• Insert battery into the PCB.
• Insert meter into printed case. When it is nearly fully inserted, use one end of the patch cable to guide the TRS jack into place (it should fit inside the indent best seen in pictures of the yellow case). Once meter is fully inserted, use two small screws at the back to secure it in place. Add knob. Test to ensure it works.

4. The minutes unit

• Cut a 6-8" length of patch cord, thread it through the hole in the minutes case (connector on the outside), and strip the end. Connect the ring wire (white) to the positive side of the meter (again changing out the resistor if necessary, and using shrink tubing).
• Using spare bits of wire from the ribbon cable as needed, connect the tip wire (red) to the tip terminal of the other TRS jack (this carries the seconds signal through), and the sleeve wire (silver) to the sleeve terminal AND the ground of the meter. The ring terminal is unused.
• Before closing up the meter, connect the cord to the hours unit and test.
• Use silicone sealant to adhere the jack in place, and insert the meter into the case, the same way as the hours unit.

5. The seconds unit

• Assembly is similar to the minutes unit, except attach the tip wire (red) to the positive side of the meter. The ring wire goes unused.
  Before closing up the meter, connect the cord to the minutes unit (itself connected to the hours unit) and test.

6. Calibration

• Per the Angular Clock instructions, you can use the Arduino IDE to calibrate the needle deflection. If you like, you can install my fork of the software that supports a 24-hour dial, more calibration points, and potential future features.