My initial blog 3rd Brake Flasher was about using an accelerometer and plug-n-play setup, with a low-cost popular GS-100A flasher. I got a few requests about an option without an accelerometer, but with some delay feature, so it would not be so annoying in stop and go traffic. The challenging part of such a design is there isn’t constant power. Power is available only during brake application. To solve this, I have added a couple of big capacitors to my design and optimized it for very low power consumption, so the microprocessor can stay powered for an extra 10-15 seconds after every brake application. The 3rd brake light will blink 4 times after the initial brake application. If intervals between brake applications are less than 10 seconds, it will simply pass through brake status.
This design option is available from my store.