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By just tying a neuron's bias resistor to Vcc, rather than to ground, you can make a "regular logic" (active high) Nv:

putting diodes and other resistors in parallel to give different charge vs. discharge rates

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We assume that the slowly changing waveform at the Nv input produces a single output transition when it crosses the Nv switching threshold. This is accomplished by using a 74HC14 or similar CMOS Schmitt trigger. When 74HC04 or 74HC240s are used for Nv inverters some nasty oscillations occur during switching which makes these inverters unsuitable for most Nv networks greater than 2 Nv in series.

The Nv neuron circuit may look familiar as it is found in most CMOS data handbooks as an example of a simple edge detector or one-shot or mono-stable circuit application.

One essential difference is that the Nv responds immediately to an input, and sends the output for a time duration -- the delay occurs AFTER the output is sent. The Nu responds to an input after a delay and sends the output continuously -- the delay occurs BEFORE the output is sent.

"on" first, then a delay, then "off"

delay, then "on", stays "on"

A device used to store charge in an electrical circuit. A capacitor functions much like a battery, but charges and discharges much more efficiently

BEAM robots tend to use capacitors in two, very different roles -- small ones in Nv neurons and solar engines (filter capacitors), and bigger ones as energy storage devices (storage capacitors).