Electronic – Teensy-LC 5v Pin

I have not used the Teensy hardware. That said, from the specifications, it looks like a nicely designed piece of hardware. The Teensy developers have done their own comparison with the Arduino, from which I'll quote:

Teensy uses a similar Atmel AVR processor as the Arduino board, but there are differences. The most important is direct, built-in USB on the Teensy compared to serial converted to USB by a separate chip on the Arduino. Teensy communications MUCH faster than Arduino. Starting with Teensyduino 0.6, Teensy can communicate as a USB keyboard and mouse, which is impossible with an Arduino board that has a fixed USB to serial converter chip.

Teensy is designed for easy use on breadboards in the smallest possible size, which is incompatible with the form-factor used by Arduino shields.

While many types of sketches can run, Teensy is NOT an "Arduino clone" due to the substantial technical differences. The Teensy hardware and Teensyduino software add-on are NOT endorsed or supported by the Arduino developer team.

Here are some other advantages that the Arduino has over the Teensy:

• Standalone operation: The Teensy can only be powered by the USB port. Therefore whatever you build around it will need to be plugged into a USB port (and most likely, a computer); if you want/need more power, you'll have to design and build your own power circuits. Arduinos offer many power options (USB, battery, wall-wart, etc) on-board.
• Easier Development Tools: Out of the box, both the Teensy and Arduino depend upon GCC and AVR-Libc. Arduino then adds the Arduino IDE, sketches, and other libraries that make getting started faster and simpler. (You can use those tools to develop with Teensy, but they aren't supported and have limitations).
• Standardized physical form-factor: The consistent Arduino form-factor allows people to develop processor and extension boards (shields) that can be shared and reused. You can see lists of those boards here, here, and here. Those lists are necessarily incomplete, because there are developers actively developing new boards continuously. Even the Arduino Mega can use shields designed for the earliest Arduinos. Different versions of Teensy use different physical forms and pinouts.
• Open development model: All of the Arduino hardware, firmware, and software are available with Open licenses that allow you to modify, enhance, and distribute your changes without fear of legal reprisals. Teensy does not offer the same protections.
• Community: There are LOTS of Arduino developers, along with websites, tutorials, books, kits, etc.

On the other hand, don't let all of that discourage your from using the Teensy if it meets your needs -- the Teensy platform looks well-designed for many applications where the Arduino would be too large or bulky.

The typical dropout voltage of the 7805 is 2.0V but you only have 6.5V input so the regulator can't work properly. This could mean that any small current spikes in demand on the load side of the regulator eg when switching on LEDs would result in voltage ripples, despite the 10uF capacitor, and PIRs are very sensitive to voltage ripples.

I'd recommend raising the input to the 7805 to at least 7.0V and probably 8.0V to allow for variations in drop out voltage (2.0V is listed as typical, not maximum), and adding an RC filter to the supply to the PIR circuit. However, you'd need to size the R carefully to avoid reducing the PIR circuit supply to less than it's specified minimum (maybe an inductor would be more effective and less loss). Another option would be to use two 7805s, one for the micro and one for the PIR circuit, with common 0V, which would prevent noise from the micro side getting into the PIR circuit so much.