The relay module should be mounted within several inches of
the sensor module so that the logic level signal does not pick up
any interference or is degraded. The light purple color that you
may be able to see in the LED nearest the camera is the camera’s
sensor seeing the infrared light being emitted by the LED.
Putting an O scale hopper over the sensor as in [9], the arrow
points to the LED on the relay module that illuminates to indi-
cate that the car has been detected and the relay has closed.
The 5VDC needed to power these modules should be reason-
ably well-filtered and regulated. While these modules do not
use any critical digital circuitry, a power pack set to 5V is prob-
ably not the way to go to supply the 5V needed.
There are many options to supply clean 5VDC: bench-top and
laboratory power supplies; open-frame power supplies and
regulated plug-in wall transformers (wall-warts) are good
choices (just be sure that the output of the wall-wart is regu-
lated and DC, not AC).
Each detector draws about 10 milliamps steady state and 85
milliamps when a train is detected and the relay is energized.
Therefore for each ampere that the power supply can provide
will power up to 50 detectors or so, given that few will be ener-
gized at any given time.
A final word
Both of these modules are sold by and will ship from vendors in
China. To allay your concerns: I have ordered many items from ven-
dors in China with complete success and satisfaction. Chinese ven-
dors offer products that are not available here and prices are very
reasonable; plus shipping is usually free. I pay exclusively via PayPal.
With PayPal the vendor does not see your credit card information;
PayPal also has a dispute resolution process as well as a refund
