somewhat negative. In this way, there will be a positive
output unless both inputs are on and combine to drive
the sum below the threshold.
+% 9 6)$ -/53%
A Neural Oscillator
Now, let’s talk about the third setting of switch
SW1. Our Perceptron is a highly idealized model of a
real biological neuron, and it would take some complex
electronics to model all of its functions. However, the
Perceptron does include one additional behavior, which
brings us to an interesting fact — Neuron Property #3.
NEURON PROPERTY #3:
A neuron has a built-in time delay.
A neuron’s operation is a complex function of time, but
for our purposes we will consider a simple time delay.
As with all real world devices, a neuron cannot instantaneously produce an output and, in fact, operates quite
slowly (on the order of milliseconds) compared to
electronic circuits (nanoseconds). But as we will see shortly, time delays are actually useful in the same way that
clocking functions are critical to digital circuit operation.
One of the extra amps on the LM324 chip has been
used to create a second neuron. This neuron only has
a single input which is the output of the first neuron. But
it also has a time delay, which is implemented by the
combination of C1 and R6. When switch SW1 is moved to
its third position, it connects an inverted version of the
first neuron’s output back as an input to itself. However,
because of the delay circuit, this doesn’t happen until
after about a second. Since the signal is inverted, it
causes the first neuron to change its state, and then keep
switching back and forth about once a second. The result
is a simple oscillator that has been created using only
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If you are new to the concept of
neurons and neural networks, the
Perceptron offers a practical hands-on introduction to a neuron’s
operation. If you are a seasoned
pro, I think you will find it to be an
entertaining diversion that is simple
to build, and makes a fun accessory
for your desk. NV
(USA & Canada)
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• on-board RS232C interface
• up to 33 I/O lines, with multi-property programmability
(e.g. direction, pull-up/pull-down,
reduced drive, invert polarity, etc.)
• up to 8 key wake-up interrupt
inputs, with digital filtering
• SCI • SPI • CAN
• 8-channel 10-bit ADCs
• multiple PWM channels
• 4-channel timers, supporting
input capture/output compare,
event counting, gated time
accumulation, and simple PWM
• 32K multi-sector Flash • 2K RAM
• operates up to 48MHz via PLL
• 3. 3 V or 5 V operation
• advanced CISC architecture
• on-chip Serial Monitor
• supports BDM debugging
ABOUT THE AUTHOR
■ Christopher McCarley is currently a
software architect at Viziqor Solutions.
He has done postgraduate research in
VLSI analog neural network design and
has 20 years experience developing a
variety of technologies including mid-dleware, robotics, and laser systems.