Nx
From BEAM Robotics Wiki
- A designation used as shorthand for an "Uncommitted neuron" circuit.
Originally referred to as a Nv/Nu, Wilf Rigter later coined the designation Nx to discribe this "uncommited neuron". An Nx is a BEAM neuron that has no fixed reference. Instead both the capacitor and the resistor act as inputs and are generally connected to the complementary outputs of a monocore, bicore or similar circuit.
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On Sun Oct 8, 2000, Wilf posted the following explanation of the Nx to the BEAM email list.
Actually with switching frequencies slower than it's own time constant, the Nx neuron behaves more like a Nu and it is the capacitor which is switched to ground or Vcc while the resistor supplies charging current from the opposite phase. The key indicator of this Nu behaviour mode is that unlike a Nv neuron, the output of the Nx does not change instantly when the capacitor is switched.
Applied as shown in the attached schematic each input leg of the Nx neuron is driven by 180 out of phase signals in this case from the master bicore. It is a bi-lateral phase delay circuit to generate a quadrature output. Here the Nx behaves as a Nu which integrates (delays) the signal from the resistor input until the 74HC14 threshold is crossed. But what makes it special is that when the signal at the capacitor input changes state it dumps the remaining capacitor charge (without changing the Nx output) so that unlike a conventional Nu, it always starts timing from "zero" (like a Nv neuron) and is therefore insensitive to the dutycyle of the input signal as long as the input pulse width is longer that the Nx delay time (again just like a Nv neuron).
The Nx neuron is also a key element in the PS head circuit where, depending on the input frequency and duty cycle, it's behaviour changes from an inverting Nu to a non- inverting Nv which is used to stop the motor and reduce power when the optical sensors are in equilibrium.
