Open Source StopWatch

This project is a simple StopWatch for measuring times on different processes or activities. The project was chosen to test some 4-layers PCBs and experiment with the XLP (Extreme Low-Power Technology) of the PIC18LF14k50. You can measure from milliseconds up to 99h.

The PCB does not have any power button, since the project's approach is to use the XLP technology of the PIC. It only has two buttons: the start/mode button and the pause/stop button.

Repository Link

Every file is on the GitHub repository

You will need the following components (For V1 revision):

• 1x PCB (Thanks to PCBWAY to sponsor this project!)
• 1x PIC18LF14K50
• 1x Green LED (0805 metrics)
• 11x NPN 600mA
• 10x 220 Ohm resistor (0805 metrics)
• 1x 100 Ohm resistor (0805 metrics)
• 11x 4K7 Ohm resistor (0805 metrics)
• 6x 10K Ohm resistor (0805 metrics)
• 1x Buzzer 5V
• 3x 0.1uF Capacitor (0805 metrics)
• 1x CR2032 Battery Holder
• 1x 4-Display 8 digits (3461AS)
• 2x Tactile Push Buttons
• 2x ZLLS410TA diode
• 1x Inverter IC (74LVC1G06GW,125)

You will find all the components, links to the components, Gerber and simulations files in the GitHub Repository.

As you can see, the design is pretty forward: The pic18LF14k50 drives some NPN transistors, which allow both displays to light. Same for the buzzer. The inverter is used so we can drive only one display at a time. (And thus, we save an extra pin of the microcontroller)

As you may know, the display has four displays in parallel (eight if you count both displays), so we will need to have a high-frequency blink in order to "trick" the human eye to see them all light at the same time. 

For the buttons, an RC filter made of a 10K resistor and 100nF will filter any bouncing effect, having a great counting experience.

The schematic is easily available in the repository

The solder paste can be applied with a syringe or stencil. Afterwards, the components should be placed with the use of some tweezers. Finally, the board is soldered with a hot air gun or reflow oven.

The components can be placed and soldered by hand. After it, you must cut the leads from the components

This can be done either before or after the TH components, as the device which we are burning is the pic18F, which uses an SMD package. You will find the code and hex files on the GitHub repository.

Fully assembly video in my YT channel :)

During Idle mode, the power consumption is 6.58mA. If the screen is OFF but the device is counting, the consumption decreases down to 1.6mA. Finally, sleep consumption is 260uA, which is pretty low.

First of all, if you like my projects, I strongly recommend you to follow us on our Instagram profile, Where you will be updated on a daily basis.

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https://makingdevices.com/links/

Finally, I would like to thank PCBWAY, the sponsor of this project. I really recommend you pay them a visit if you are thinking of ordering some Gerbers at any time in the future. I am truly impressed with how good they work and the high quality of their PCBs.