MULTICHIME DIESEL HORN
DH-1
211 RocBaar Dr., Romeoville, IL 60446
(815) 886-9010 FAX: (815) 886-9076
Electronics for Model Railroads
GENERAL DESCRIPTION: The CIRCUITRON DH-1 is a highly realistic, all electronic diesel air horn
simulator. The three frequencies reproduced by the DH-1 closely match those produced by the Leslie
Company’s famous S-3L Supertyfon air chime. Each chime on the DH-1 is individually controllable so that
many different tone combinations are possible. It is, in fact, possible to produce seven different horns
using just the one DH-1 circuit board. These would be as follows: single low tone, single middle tone,
single high tone, low-middle dual chime, low-high dual chime, middle-high dual chime, and the low-
middle-high 3 chime horns. These various combinations are switch selectable. With the addition of extra
speakers, these various tones can be produced at any point on a layout. The DH-1 requires a 10-18 volt
AC or DC input for proper operation.
CIRCUIT DESIGN: The DH-1 uses a CMOS integrated circuit configured as three square wave
oscillators. Each of these oscillators are adjusted for the proper frequency output at the factory. The
outputs from the three oscillators are combined and drive a darlington output transistor to achieve the
necessary current gain to drive a speaker.
INSTRUCTIONS: The DH-1 can be connected with .110" solderless connectors (available from
CIRCUITRON) or by soldering leads directly to the terminals on the printed circuit board. If soldering, use
a small pencil-type iron and electronics-grade rosin core 60/40 solder (available at Radio Shack). Use only
as much heat as necessary to obtain a good joint and do not wiggle the terminal until the solder has
cooled completely. A section of CIRCUITRON’S PCMT can be used for simple, snap-in mounting of the
circuit board or you may drill holes in the mounting pads in the corners of the board and mount the DH-1
with screws and standoffs.
MOUNTING THE SPEAKER: For proper reproduction of the lower frequencies produced by the DH-1, the
speaker supplied must be mounted in some sort of enclosure. A small box can be constructed of wood
with a 2” round hole cut in one side. Mount the speaker to the inside of the box, centered over the hole.
A silicone sealant, such as aquarium or bathtub caulk, is ideal for cementing the metal speaker frame to
the box. Do not get any of the sealant on the paper speaker cone. After the silicone has cured
(overnight), solder two wires to the speaker terminals and run them through a small hole in the side of the
box. Seal the box with a cover of wood fastened with screws so that access to the speaker is possible.
Mount a small piece of window screen or grill cloth across the speaker hole to protect the cone from
damage.
It is also possible to use the layout mounting board as the speaker baffle. Cut a 2” round hole through
the board at the desired location. Mount the speaker to the underside of the layout using silicone caulk as
above. Place a piece of window screen or grille cloth across the hole to protect the speaker cone from
damage.
NOTE: The 2 1/4” speaker supplied with the DH-1 is rather inefficient. Although it is adequate for most
small layout applications, if you care to substitute a larger diameter high-fidelity speaker, the volume and
tone will be dramatically improved. Radio Shack sells suitable speakers for automotive and stereo
applications. A 5”-6” diameter is ideal. The speaker should be rated 8 ohms impedance. If you require
even greater volume, the circuit board can be modified. Consult the factory and request application note
AN5701-1.
CONNECTING THE CIRCUIT BOARD:
1) Solder two light gauge (22-24 ga.) wires to the terminal strip on the speaker. These wires must be
long enough to reach the circuit board and pushbutton locations.
2) Mount the pushbutton on the control panel.
3) Connect one wire from the speaker to the Speaker Terminal on the circuit board labeled [-].
