Parallax.com (#555-28027) from a 12
VDC-100 mA power supply, but don’t
know how to connect the two together.
Can you create a schematic on
how to turn on the IR Illuminator
whenever the PIR module detects any
heat/movement and turn it off when
no heat/movement is detected?
Please indicate whether I should
use a 12 VDC-500 mA rather than a
12 VDC-100 mA power adapter.
— Don Franklin
AThe IR illuminator has six diodes in series which each drop 1.5 volts plus 78 ohms in series; there are four strings
in parallel. With 12 VDC applied, there
are three volts across 78 ohms which
gives a current of 38. 5 mA and 154 mA
total; therefore, you need a power supply
rated at least 200 mA or 500 mA.
The sensor operates on three or
five volts, so you need a regulator. In
Figure 2, I show an LM2931 five volt
regulator which is in a TO-92 package.
The sensor output goes high when
movement is sensed, which turns
on the logic level FET to power up
the illuminator. The ZVN4210A is
also in TO-92 packages.
QCan the circuit in Figure 3 be converted to use a PIC? I’m sure all these chips can be substituted with a
microcontroller of some kind.
U1 is for sequel output.
U2 is a divide by two.
U3 seems to be two slaves.
U4 is a modulator of some kind,
I think PWM.
U5 is logic combiner possibly.
U6 is a dual clock using 556.
One other thing ... the two
■ FIGURE 2.
transistors go to another part of a
circuit off this circuit.
— Craig Kendrick Sellen
AA microcontroller can only do one thing at a time and this circuit has two independent oscillators, so it
is not possible to directly translate this
circuit to a microcontroller. However,
if the inputs and outputs are described
November 2011 23
■ FIGURE 3.