Specifications

34
This was ideal for the purpose of the robot and so more of these chips were obtained.
The Z1955 datasheet details a suggested bypassing and filtering circuit containing a few
resistors and capacitors. A single circuit board was soldered containing three of these
bypassing and filtering circuits and three receiving chips. Testing of these revealed that
the first prototype circuit still worked fine, however the two new circuits (identical in
every manner) would only work at a distance of approximately 20mm. Due to the fact
that one of the receiving circuits worked successfully, the mistake was made of
assuming that the IR transmitter circuit was without fault. It wasn’t until after many
hours of testing and different circuitry being implemented that it was found to that the
555 timer circuit was causing relatively large voltage spikes in the power supply in time
with the 38 kHz light pulse. Due to the fact that the emitter and receivers were being
powered from the same voltage supply, the noise was affecting the operation of the
receiver chips. It is still unsolved why one chip worked and the remaining two failed;
however overcoming this problem initiated some desired results.
A group of capacitors wired in parallel on the input of the transmitter circuit provided a
noise filter to the power supply. A combination of a large Electrolytic capacitor,
medium Tantalum capacitor and a small Monolithic capacitor provide an effective noise
filter to combat fast ripples in the power supply. The following schematic details the
chosen capacitors and placement in the power supply circuitry.
Figure 4.14: Power Supply Filter for Transmitter
An LM7805 voltage regulator is used to supply the 5 volt source from the same battery
that supplies the Motorola HC12.