■ PHOTO 1. Here is the FFT
of the pulse taken at the
wrist. Note that this is a
linear scale. It is also
noteworthy that no signals
above 10 Hz were seen.
The Power Supply
mean there aren’t any).
Going further, it would not be
■ FIGURE 1. The schematic diagram of the
project consists of three sections: power
supply, amplifier, and conditioner. This is a
high-gain, mixed-signal design that requires
proper techniques to function accurately.
surprising to find that a
normal human pulse wave
would have a soliton wave
shape. After all, nature has
had a long time working
out the kinks in circulatory
systems and a soliton wave
is very efficient. (Soliton
waves are self-reinforcing waves that
propagate without distortion based on
non-linear characteristics of the
medium.) Photo 1 shows an FFT of
my (mostly) normal wrist pulse. It is
unknown if this matches a soliton
wave. (If you know, please tell me.)
Figure 1 is the schematic diagram
of the pulse speed timer. There are two
important things to note right away.
The first is that this is a mixed-signal
design. Both analog and digital components are used. The second is that
the analog section has amplifiers with
gains of 1,000. Putting all this together
will require some special attention.
The power supply section is
pretty much basic, except that there
are a few subtle points that need to be
discussed. When working with high-gain and/or mixed signal designs,
power-supply (PS) noise can be a real
problem. PS noise shows itself in two
different ways. Obviously, it doesn’t
take much noise to drown out your signal. This is especially true with low-level
signals requiring high-gain amplifiers.