Teensy 2.0 Schematic

A 3.3 volt MCP1825 voltage regulator (shown in gray, full part number MCP1825S-3302E/DB) may be soldered to the bottom side. Three pads allow a solder bridge to configure for 5 volt or 3.3 volt power. The 5 volt pads are linked when the board is shipped.

Teensy++ 2.0 Schematic

A 3.3 volt MCP1825 voltage regulator (shown in gray, full part number MCP1825S-3302E/DB) may be soldered to the bottom side. Three pads allow a solder bridge to configure for 5 volt or 3.3 volt power. The 5 volt pads are linked when the board is shipped.

Four extra parts may be soldered to the bottom side of the Teensy++. These are shown in gray. A 32768 Hz crystal may be connected to E4 & E5 for the timer2 oscillator. An extra power supply decoupling capacitor may also be added, located close to the AVcc pin.

The ALE pad should only be used as an output signal. If this pin is driven high while the reset button is pressed and released, the board will not run the Halfkay bootloader.

Teensy 1.0 Schematic

The D7 pin requires special care, because it is also the HWB signal that determines if a reset pulse will reboot to the bootloader or the user application. The simplest way to use D7 as an output, driving a load to ground (but not a pullup resistor), or as an input for a normally low or open collector type signal. If a circuit is attached to D7 that acts as a pullup resistor, it could charge the 1uF capacitor before the chip finishes reset and reboots.

Teensy++ 1.0 Schematic

Four extra parts may be soldered to the bottom side of the Teensy++. These are shown in gray. A 32768 Hz crystal may be connected to E4 & E5 for the timer2 oscillator. An extra power supply decoupling capacitor may also be added, located close to the AVcc pin.