Specifications

33
Figure 4.12: PCB Inside LED Torch Figure 4.13: LED Torch Complete
With Wires
The IR receiving diode should have responded with a voltage drop or even a noticeable
resistance change when presented with the torch; however no change was found
whatsoever. To check the frequency response of the chip, a function generator was
hooked into the base of the transistor at the output of the 555 circuit. The chip was
tested for response from 1 Hz up to a few hundred kHz but absolutely no response was
found. No datasheet was available for this chip as it was sold solely and had no
markings to distinguish it by. After reading other circuits that seemed to contain similar
chips, it was found that a pull-up resistor was most likely necessary for correct
operation. By adding a 2k2 ohm pull-up resistor to the output of the receiving chip a
change of approximately 0.5V could be obtained over a distance of 100mm. This was
far from ideal however a comparator circuit would be able to turn this small analog
signal into a clear digital response. It wasn’t until the comparator circuit had been
constructed on a breadboard that it was found that sunlight shining through a window
was affecting the response of the sensor. Due to the large complexity of the comparator
circuitry to achieve such a simple task, it was decided to scratch this idea and start from
a different perspective.
After a lot of searching on the internet for different IR receiving components, a DSE
component, part number Z1955, was discovered that claimed to provide a digital signal
in relation to the presence of 38 kHz light. This seemed much more practical than the
analog signal chips, as measuring distance is not a requirement of the Mobile
Manoeuvring Robot. After powering up the new chip and shining the torch off the 555
timer circuit a 5V drop could be obtained over a distance of approximately 500mm.