NPC Model 8010SD Railguard
Electronic Horn
For Light Rail Vehicles


The electronic horn consists of a controller, a speaker, and an accessories connector. The controllers have a switching power supply that transforms the 24Vor 36V DC nominal input to +/-50V for the power amplifier and 16V for other functions. The controller also has an audio board that stores the digitized signals and has a microprocessor that plays them back when required. The third board in the controller is the power amplifier that provides relays that are activated by the horn control switches in the LRV and an audio amplifier to drive the speaker. The relays request the audio board to send the audio signal and provide isolation from the LRV horn control switches.

The speaker is an HPC-370GA from Atlas Sound or similar. Two speakers can be used to increase sound levels.

The accessories connector is the mating part to the connector on the back of the controller that is used for wiring the power, switches, and speakers to the controller.

The electronic horn is designed to produce about 95dB SPL at 100 feet using 1 speaker and is capable of being adjusted from 0 to about 96dB SPL. A second speaker can be added to increase the sound levels or add redundancy. There are provisions for a second horn switch that can be adjusted separately to any level up to about 96dB and is shipped from the factory set at a level to produce about 85dB at 100 feet. A bell tone is also included in the controller. Other sounds are optional.

The unit can be used for external messages as well as horn/whistle/bell sounds. One such message might be “Train approaching, stand back from the track”. Internal messages can be sent from the audio board to the intercom system such as “the left door is closing, please keep clear”.

The “standard” audio sounds are:

High horn
Low horn

The high horn and low horn are the same sound, adjusted for different output levels. The horn is activated as long as the input is active. The bell can be wired to finish the tail of the bell sound as long as the Trackway signal is not needed, otherwise it stops immediately when the input stops. The Left Door Close, Right Door Close, and Trackway signals are momentary triggers, so the message finishes after the input is activated unless the horn or bell input is activated.

One spare is provided that operates like the horn.

The audio recording is 44.1kHz 16 bit .wav file or similar. There is a maximum of 11.88 seconds of recording possible with the standard memory provided. Because the audio can repeat, only one bell strike is required and only about 1 second of horn sound is required.


These pin numbers correspond to pin locations of the circular connector on the back of the control unit.


2 Speaker return. Use 18 AWG or larger wire.
3 Speaker +. Use 18 AWG or larger wire.
4 -Vin (battery minus)
8 System ground (to connect to horn/bell switches)
9 System ground (to connect to horn/bell switches)
11 Spare sound switch.
13 Bell Switch (attach normally open switch and close to ground to activate)
14 High Horn Switch (close to ground to activate)
15 +Vin (battery positive. Can be 22 to 48 VDC at up to 15A)
17 Other audio to public address system (input)
19 LDC switch
20 Low horn switch (close to ground to activate)
22 Audio now to public address system (output)
23 RDC switch
24 Trackway switch


There are potentiometers on the Power Amplifier board with the top one being for High Horn, the next one down for Low Horn, and the third one for the Bell. These potentiometers are accessible through holes in the upper right quadrant of the front cover without opening the control unit by using a very small flat bladed screwdriver or pot adjustment tool. They adjust clockwise to increase output level. The remaining potentiometers are accessible by removing the front cover. R7 is used to adjust the spare sound.