Think of the littleBits threshold as a toll booth for signal passing through your circuit. The threshold compares the incoming voltage coming from the bit snapped before it against the voltage amount you’ve set by the threshold knob. If the incoming voltage value is greater than the selected voltage, the threshold will allow the signal to pass and activate any bits (lights, motors, etc…) following it. If not, then nothing will be activated. Use it to make any sensor module into a trigger module!
The threshold is a minimum parts count design, using only a single opamp to accomplish the task of comparing the input signal to an onboard reference that is set via the potentiometer control. U1 is configured as a non-inverting comparator with approximately 100mV of hysteresis provided by R1 and R3. VR1 provides the comparator's reference. C1 is a bypass capacitor for U1 that sources current to the opamp during fast switching events.