Digit

CapyTimer

CapyTimer is meant to be a simple timer for boxing/kickboxing/grappling/fitness. My goal is to keep its interface as simple as possible while maintaining the most important functionality. Work and rest times are set with dials, and the timing started and stopped with a switch or button. The display counts the remaining time, the current round, and nothing else.

The display is constructed from WS2812B addressable LEDs. The original plan was to cut up and solder three-LED sections to create the digits, but that proved time consuming and ugly so I ultimately designed a PCB for the digits with the LEDs pre-placed. You can follow the original plan and save some money by cutting up and soldering a WS2812B strip, or just order the PCBs preassembled from JLC (or just get the boards manufactured and solder on the LEDs yourself).

This isn't really meant to be a prescriptive set of instructions for building the timer exactly a certain way. I've provided components here and I'll lay out a general path towards putting it together, but you should feel free to substitute different controls and alter the presentation to your liking.

Warning - The remote control design is currently untested. I think the parts will all fit properly, but I'm still waiting on the final PCBs to test with and can't guarantee that the design works yet.

Directory Structure

• 3d/ - Files for 3D printing. These include the digit and separator diffusers, the remote control body, and a set of printed frames to hold the digits for testing purposes.
• firmware/ - Code to run the AVR microcontroller. Specifically this expects an Atmega328P, the avr-gcc toolchain and a USBasp programmer. If you deviate from these specifications you may need to alter the firmware and makefile.
• pcb/ - KiCad schematics and PCB designs. This includes the main control board, boards with the LEDs laid out for the digits and separator, and a control board for the remote control. With the exception of the remote control board (which is simple enough to easily hand solder), I've included gerbers and BOM/placement files that you can use to have the boards manufactured by JLCPCB. These worked as of this publishing, but be warned that some parts may go out of stock and need replacing (they already switched to a new version of the WS2812B LEDs while I was working on the boards).
• enclosure - SVG designs to cut a front for the timer using the Shaper Origin. You'll have to adapt these if you use a different CNC.

Assembly Instructions

Please don't consider these instructions exhaustive, but more general guidance. You'll want to have some experience with electronics, soldering and crimping connectors before getting started on this, as well as some way to build an enclosure for the timer (I build mine out of wood).

Materials

Note that this doesn't include surface-mount components on the PCB, only the parts you'll need to manually assemble. If you intend to hand solder the PCBs, consult the schematics for part listings.

The Display

The display uses six digits and one separator between the minutes and seconds. You can have the digits and separator LEDs pre-assembled on a PCB by JLCPCB using the files in the pcb/ directory, or you can buy a strip of WS2812B LEDs and glue them into the 3D printed diffusers. If you do so, you'll want to use 3 LEDs per digit segment and one for each of the dots in the separator. The LEDs should be laid out in the same order that segments normally come in a seven segment display.

If you get your LED PCBs pre-assembled, you'll still need to solder on the connectors. Use one three-pin JST-PH connector for each connection. Be sure to solder these on the back side of the board so you can plug in to them while the front of the board is seated in the diffuser.

When printing the plastic diffusers, I like to use white filament for the first few layers and then switch to black. This will minimize light bleeding between segments while the display is in use. If you use PCBs for the digits and separator, the diffusers have holes for threaded inserts. You can then use the M3x6 screws to attach the boards to the diffusers.

The Control Board

Assuming you get the control board assembled by JLCPCB or some other manufacturer, you'll just need to solder the connectors and a few potentiometers onto the control board. These include the DC barrel jack for power, JST-PH connections for the screen, potentiometers and push buttons, the AVR-ISP header, the header for the diagnostic jumper (optional) and the angled header for the QIACHIP receiver module (optional, only required if you want to use the remote control). The two 3386P potentiometers are used for volume and brightess control and should be soldered directly onto the board.

The JRESET1 connector is currently unused and can be safely ignored.

To program the microcontroller, just connect the ISP header to a USBasp programmer. You'll need the avr-gcc toolchain and avrdude installed. You can then run make fuse to program the fuses on the chip, and make program to transfer the firmware. After that the timer should just work when everything is plugged in.

Connections

• Solder a DC barrel jack connector onto J1 for power.
• Connect four potentiometers to the 3-pin JST-PH connectors on the top-left corner of the board. These will set the minutes and seconds for the work and rest periods. The names on the silk screen are abbreviations for the function of the potentiometer, e.g. JWM1 is the connection for the potentiometer that controls the minutes of the work period. For these connectors, pin 1 is ground, pin 2 is signal, and pin 3 is +5v.
• The display connects to JOUT1 and JOUT2 via 3-pin JST-PH connectors. Pin 1 is ground, pin 2 is signal, pin 3 is +5v. As long as you connect the same pins on each end of your cables everything should work. The WS2812B LEDs are daisy chained, so JOUT1 should connect to the JIN1 connector of the first digit, then its JOUT1 connector should connect to the JOUT1 of the next digit, and so on. Connect the digits and separator for the time first, and then the two digits for the round display. Finally, you can connect JOUT1 on the last digit to JOUT2 on the control board. This final connection is for power only, to reduce the current that needs to flow through the first connection between control board and digits.
• The start and stop buttons should connect to the 2-pin JST-PH connectors labeled JSTART1 and JSTOP1. JRESET1 is unused. These connectors have no polarity, they just need to be normally open and close when the buttons are pushed.
• Connect an active piezo buzzer to the 2-pin JST-PH connector labeled JBUZZ1.
• You may optionally solder a 3 pin male header to JDIAG1. Place a jumper across the right two pins for normal operation: shifting the jumper to the left will put the timer in diagnostic mode, which displays the raw ADC value from the work minutes potentiometer for debugging purposes.
• If you intend to use a remote control, solder 7 pin female header, preferably right-angle, to JRF1. You can then insert a QIACHIP receiver module directly into the header.

Enclosure

The enclosure is largely left as an exercise for the reader. You'll want to select potentiometers and push buttons that fit your desired aesthetic, and you may also wish to add features like an on/off switch and external power inlet to the enclosure.

Because of the size of the timer, I haven't included a 3D printed enclosure design. Even with a 400x400 print bed, it would be prohibitive to fit all six digits and the controls. I have, however, included two 3D printed frames that can hold the digit diffusers up (with CA glue). These aren't suitable for production use, but served me well during development.

For production use, I build my enclosures as open-backed wooden boxes with a front panel that has pockets routed in for the digit diffusers, controls and the piezo buzzer. I use a Shaper Origin to make the cuts in the front panel, and you can find the SVG files for my design in the enclosure/ directory. I've only tested these with the Shaper, and expect that other CNCs will probably need some work to adapt them.

Remote Control (Optional)

With a QIACHIP receiver and transmitter set, you can also build a remote control for your timer. The pcb/ directory includes a small PCB to tie the QIACIP transmitter to some tactile push button switches and two AAA batteries.

For the remote control board, you'll need to solder on two pull-up resistors, two tactile push-button switches (use switches tall enough to poke up through the remote body), and a connector for the batteries (or just solder the battery connectors directly to the board). Add right-angle header for the QIACHIP transmitter, and solder on an antenna to JANT1.

The top remote component has holes for three heat-set inserts and four 5x1mm magnets, which should be glued into place. You'll also want to glue in the four battery contact plates, alternating positive and negative plates between the two battery slots. Solder the two plates at the bottom of the remote together, and then solder wires on to the connectors towards the top.

Glue opposite-polarity magnets into the remote lid to hold it on to the body. You can then attach the PCB and the remote body bottom to the top by using the three M3x12 screws. This connection is inherently weak because the stems holding everything together are stressed perpendicular to their layers, so be careful not to tighten the screws more than necessary to hold everything together.

Afterword

This should give you a rough idea of how to assemble one of these timers, but the instructions aren't exceedingly detailed and leave a lot of room to make the project your own. If you attempt to build one and run into problems, feel free to submit an issue. And if you come up with a design improvement, pull requests are welcome.