POINT INDICATOR BOARDS
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POINT INDICATOR-STANDARD lights control panel mounted LEDs to show the
settings of points operated by solenoid point motors. As solenoid point
motors require a momentary contact to operate them they are operated by
momentary action toggle switches, push button switches or stud and probes.
None of these show the setting of the points.
The Point Indicator shows the direction of 4 points. The setting of each point is shown with 2 LEDs (intended for wiring back to a control panel). The Point Indicator has a memory which remembers the point settings whilst power is turned off.. The diagram shows the usual/existing wiring to operate the points as brown and grey lines and the extra wiring for the point indicator as blue, red and green lines.
Point Indicator will work with points powered from either a CDU (capacitor
discharge unit) or an AC transformer. Points powered by a CDU must be wired so that the common connection to the point motors is
from the negative side of the CDU (see later for common positive
version). The positive connection from the CDU is
connected to the point motor via the switches. See the diagram above. The
reason for this is that the Point Indicator board senses positive pulses
from the switch to the point motor. The Point Indicator can be powered
from 12 volts to 24 volts to allow it to work from the supply used for the
The top 2 point motors in the diagrams are shown wired as "Peco" point motors, these have 4 connections. The bottom 2 are "Seep" which have a common connection in the centre of the point motor.
|The Point Indicator can be supplied with red, green or yellow 3mm dia.. LEDs. For example green is lit when a point is set to the main route, red when set to a subsidiary route. Alternatively all yellow LEDs can be used to represent a diagram inside a signal box. The Point Indicator uses the fact that LEDs only light when the current passes in one direction. This allows two wires to operate 2 LEDs as the point indicator reverses the voltage at the terminal block. Current either flows from L1A to L1B or from L1B to L1A.|
|It is possible to connect an extra pair of LEDs to the point indicator. The diagram below shows how the LEDs are wired. Note one leg of the LED is a little longer than the other; this is to show the polarity of the LED. (LEDs only light if the current flows in the correct direction)|
|Wiring for an LED to light the track selected|
|If the point is set to "A" then the long leg of A will be positive, hence A will light but "B" and "C" cannot lightas their short legs are positive. If the point is set to either B or C, A will not light (the long leg is negative), but either B or C can light depending upon the setting of the second point.|
POINT INDICATOR-SO (Switching Output)
|This version of the Point Indicator has a more powerful output to switch numbers of LEDs, relays or operate inputs of the IRDASC units.|
|The Point Indicator-SO has an output stage composed of open collector npn transistors. This gives many options when using the Point Indicator-SO. If you are unfamiliar with transistors the output stage is equivalent to the diagram on the right and can be thought of as consisting of 4 changeover switches with the common terminal of each switch connected to the negative terminal. This means that when the point switches one way, terminal "L2A" will be connected to "-" and "L2B"will be an open circuit. When the point switches the other way, "L2A" will be open circuit and "L2B" connected to "-". (open circuit means no electrical connection is present on the terminal)|
|The Point Indicator-SO allows a number of LEDs to be switched at the same time. This may be required for layouts with several operating positions.|
|The diagram shows how to connect a number of LEDs. If the point indicator board is powered from AC then it is necessary to use a diode to protect the LEDs from being damaged from reverse voltages. LEDs only light when current flows through them in one direction. This direction is generally indicated by the LED having a long and a short leg. A resistor value of 1K8 (1800ohms) should be suitable unless a large number of LEDs are used in which case a lower resistor value may be necessary to keep the LEDs bright. Note how the short leg of each LED is chained to the long leg of the neighbouring LED. Also note that the diode must be correctly orientated. (A diode is a one way valve for electricity) . This is shown by the band on the diode.|
|The output stage can switch relays. Two relay coils are shown connected to terminals L2B and L3B. As commonly used relays require smoothed DC (usually 12volts) to operate, a separate power supply may be required for the relays. The wiring for this is shown in the diagram|
|The outputs may also be used to operate "OI" inputs of the IRDASC signal control units. If relays and LEDs are being used it will be necessary to use a diode. The outputs can also be used to operate 4 bulb or LED signals, one on each track approaching the point.|
|Common Positive Versions|
|Some DCC accessory decoders and some manufacturers' ready built switch/CDU units use common positive point wiring i.e. the CDU positive goes to the common of the point motors. We can also supply versions of the Point Indicator and Point Indicator- SO for this type of wiring.|
|The Point Indicator Relay detects the position of 4
solenoid point motors. When a solenoid point motor is switched the point
indicator lights an LED and switches a relay. The setting of each point is shown with 2 LEDs (intended for wiring
back to a control panel). The Point Indicator has a memory which remembers
the point settings whilst power is turned off. The diagram shows the usual wiring to operate the points as
dashed lines and the extra wiring for the point indicator as solid lines
|Wiring To Relay Contacts|
|Along the bottom of the diagram are 12 terminals grouped in 3s. These allow connection to the relay contacts. When, for example, the switch connected to the input 1 terminals is operated the LEDs connected to the terminal 1s on the right will change and the relay contacts connected to terminals 1 on the lower row will also change. The relay contacts are SPDT i.e. identical to a changeover switch. "C" marks the common connection. No power is on these contacts.|
|The diagram above shows the internal contacts present in each of the 4 relays and how to connect these to switch the frog of a point. This overcomes problems with poor contact between the point blades and stock rails. These seem to be more troublesome with small gauges. The relays are also useful for switching signals.|
diagrams on the right show how the POINT INDICATOR- RELAY switches
electricity to the appropriate rails. This overcomes problems with poor
point blade contacts.
These diagrams show electrofrog points. The Point Indicator works equally well for insulfrog points.
|Voltage 12 to 16 volts AC or DC. Length x Width 80 x78 mm|