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• Project 5: Controlling message screens by switches or external devices
In addition to controlling screen messages by Track Sensors, Train direction, DCC points etc, you
can also control them using conventional switches such as push buttons, toggle switches or reed
switches (which are activated by magnets) connected to the inputs.
Always turn all power off before connecting wires and soldering!
There are two solder pad inputs on the back of the Smart Screen marked A and B and the
common solder pad is marked C and the inputs are activated by connecting the inputs A or B to
the common C. You can connect to and use either or both inputs, but be careful when soldering a
wire to the C pad as it is close to the L reset pad - take care not to accidentally bridge C and L!
Input functions
• If only one or two messages are stored in the memory:
Activating input A displays message screen A; Activating input B displays message screen B
• If more than two messages are stored (ie
anything
in message screens C to J):
Activating input A or B cycles round the messages, one screen at a time for each activation
The following shows a selection of different devices which can be connected.
Example 1: Push button connected to input A and reed switch connected to input B
Example 2: Single pole Toggle switch wired to inputs A and B to switch between A and B
Example 3: Controlling Smart Screen from a system
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Technical knowledge required
Smart Screens may be connected to other train control or hobby computer systems such as
Arduino using these inputs, though this is a specialist use for which we cannot provide technical
support, so please do not attempt this unless you understand electronics. The internal circuitry of
the smart screen operates on just
3 volts
, so we strongly recommend you link the Smart Screen to
your system via a suitable low voltage opto-isolator to protect both sides. There is a pullup resistor
on both Inputs A & B so an open collector output opto-isolator will also achieve level shifting.
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A B
P
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P
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L
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C
Power
Input
A
Input B
co
mmo
n
Power
Switch A
Switch B
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A B
P
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P
© Train
Tech.com
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L
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C
Power
Power
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A B
P
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© Train
Tech.com
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L
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C
Power
Power
Push button
Toggle switch which
selects between
input A or input B
Reed Switch
A Reed switch
is a small
glass tube containing 2 fine
contact wires very close
together but not touching.
When a magnet gets close
the contacts touch and
makes the circuit. Can be
used for detecting trains etc
If you fit switches quite a
long way from the Smart
Screen the wires may be
prone to pick up interference
such as motor noise etc.
To suppress this fit a small
100nF capacitor in parallel
with the switch connections
