PPI4-DC Model Railway Points Position Indicator - 8 Points

About the Product

The BLOCKsignalling PPI4 is a model railway points position indicator that monitors up to 8 sets of points and displays their last operated position using LEDs on a control panel or mimic board.

When a set of points is operated, the PPI4 detects the brief positive switching voltage applied to the point motor and automatically updates the corresponding LED indication. Only the LED representing the most recently selected position remains illuminated, providing a clear visual indication of the last point operation.

The PPI4 provides 16 opto-isolated input channels for monitoring up to eight pairs of point positions. Input states are automatically stored in memory, so when power is switched off and restored, the panel LEDs return to their previously recorded states.

Designed for model railway control panels and mimic boards, the PPI4 also includes adjustable LED brightness and built-in diagnostic LEDs to assist with installation and troubleshooting.

Key Features

• Monitors up to 8 sets of points.
• 16 points-monitoring input channels.
• Displays the last operated point position using control-panel LEDs.
• Automatically remembers point positions when power is switched off.
• Adjustable LED brightness.
• Opto-isolated points inputs.
• Accepts points-monitoring voltages from +5V to +25V.
• Built-in input and output diagnostic LEDs.
• Suitable for control panels and model railway mimic boards.
• Supports red and green route indication LEDs.
• Compatible with suitable dual-colour LEDs.
• Can be used to automatically control compatible 2-aspect signal LEDs from point operation.
• Supports 3-way points with suitable additional wiring.
• Optional programming – no programming required for normal operation.
• Built-in LED lamp test function.

Points Position Indication

The PPI4 monitors the brief switching voltage applied when a point motor is operated.

Each set of points uses a pair of inputs. When one input receives a positive switching pulse, its associated panel LED is selected and the other LED in that pair is switched off.

This means the control panel continues to show the last operated position of each set of points, even though the electrical pulse used to operate the point motor lasts only briefly. 

The diagram shows a typical PPI4 installation, with the module monitoring the point motor switching circuit and displaying the last operated position using LEDs on the control panel.

Monitoring Up to 8 Sets of Points

The PPI4 provides 16 input channels (I1–I16), allowing it to monitor up to 8 sets of points.

Each input controls the corresponding LED indication, making the PPI4 particularly useful for larger control panels where the operator needs to see the last selected route at a glance.

Automatic Position Memory

Each time the PPI4 detects a change in point position, the new state is automatically stored in memory.

If power to the layout or PPI4 is switched off, the stored positions are retained. When power is restored, the LED outputs automatically return to their last recorded condition.

Control Panel LED Indication

Red and green LEDs can be installed on a route mimic or model railway control panel to provide a clear indication of the last operated position of each set of points.

Each LED requires a 1kΩ series resistor and must be connected with the correct polarity. Incorrectly connecting the LEDs in reverse can cause them to fail and may damage the PPI4.

The diagram shows the correct connection of the red and green panel LEDs. Each LED must be fitted with a 1kΩ series resistor and connected with the correct polarity.

The PPI4 can also be used with suitable common-anode three-leg dual-colour LEDs with built-in resistors.

2-Aspect Signal Control

The PPI4 can also be incorporated into suitable 2-aspect model railway signal arrangements.

By wiring red and green LEDs appropriately, signals can automatically indicate which route through the points is clear. For this arrangement, the signal LED connections must be individually accessible rather than using a common-anode or common-cathode signal head.

This arrangement allows a pair of red and green signal LEDs to automatically indicate which route through the points is clear.

Full wiring information is provided in the instruction manual.

Points Motor Compatibility

The standard PPI4 is designed for point-control systems where the point motor coil common is connected to ground (negative/common GND).

The opto-isolated inputs accept positive switching voltages from approximately +5V to +25V.

When using solenoid point motors, a Capacitor Discharge Unit (CDU) must be used to prevent damage to the PPI4. Points directly powered from an AC supply must not be connected directly to the PPI4.

For Kato points, BLOCKsignalling also produces a dedicated PPI4-K version. The standard PPI4 can be used with Kato and Cobalt points using the additional wiring arrangements shown in the instruction manual.

Diagnostic LEDs

Built-in LEDs provide useful information during installation and troubleshooting.

The red uP LED indicates that the microprocessor is operating, while the yellow IP LED flashes when a point operation is detected. Changes to the stored point position are also indicated by the module during operation.

Electrical Requirements

• Power Supply: Regulated 12V DC
• Typical Current Consumption: Approximately 50mA with all panel LEDs illuminated
• Recommended Power Supply Rating: 0.25A to 1A
• Points Input Voltage: +5V to +25V
• Number of Inputs: 16
• Points Capacity: Up to 8 sets of points
• LED Series Resistor: 1kΩ per LED
• Points Input Type: Opto-isolated
• Point Motor Common: Ground / negative common

The PPI4 should be powered from a regulated 12V DC supply. Do not power it from an unsuitable auxiliary accessory output on a train controller, as these outputs may not provide a sufficiently smooth or stable supply.

A compatible regulated power supply is available separately: PSU2 12V DC 1A Model Railway Power Supply.

Documentation & Support

For complete installation instructions, LED wiring, points connections, programming, additional applications and troubleshooting guidance, please download the latest PPI4 instruction manual:

Product Instruction Manual