Federal Signal A11 AF Timer (Modern Tech)

This is a specialized AF timer build I made for @nascarsimraci_903773's excellent ⅓ scale 3T22A model.  It's not built for an original Federal Signal A11 board or switches, but is built to resemble it.  Instead, I utilized a multiple-voltage power supply and Raspberry PI as the electronics.

In addition to the parts here, this model is designed around @mattwatson's AF timer plate and button cups:

• https://www.printables.com/model/384348-af-timer

Grab that, and the models here, and go to town.  I included a remix of the button cups with a smaller inner diameter that works with the buttons used here.

Printing

To print, use whatever brand PLA or PETG suits you.  For accuracy, you should grab at least the following colors:

• Orangy-yellow for the box and yellow button cup,

• Red for the timer face plate, red button cup, and red part of the CD logo,

• Blue for the blue button cup and blue background of the CD logo,

• White for the white button cup (or use grey here), white text of the face plate, and white part of the CD logo,

• Black for the black button cup

All parts are already oriented correctly for printing, and should not need any supports.

For all parts, I recommend at least 20% infill.

For the face plate and white/red parts of the CD logo, you'll want to use your slicer to add a color change there.  I printed the face plate with a red background and white text, and the triangle part of the CD logo with a white background and red “CD”.

The rest can be printed in one color.

Mechanical Assembly

To assemble, I used the following:

• 8x M4x12 screws

• 2x M4x16 screws

• 2x M4x30 screws

• 4x M4 nuts

The model is designed to be printed on smaller printers (such as my Neptune 4 Pro), so the box comes in two halves.  Assembly is done as follows:

1. Align the bottom parts of the box together, using the cone aligner as a guide.

2. Use 2x M4x30 screws for the top two screws, and secure with 2x nuts.

3. Use 2x M4x16 screws for the bottom two screws, and secure with 2x nuts.

This completes the bottom part.  For the lid:

1. Use 8x M4x12 screws to attach each half of the lid to its spot on the box.

2. Glue the timer plate on the bottom-half of the lid, embedded in the recess.

3. Glue each button cup to the timer plate.

4. Glue the blue CD logo part into the circle cut-out of the top half of the lid.  The triangle should face up to the top of the box.

5. Glue the rest of the CD logo into the recess of the blue background piece.

Electronics

For the electronics, I used the following parts (all available on Amazon):

• Raspberry PI Zero 2 WH (make sure you get the one with the header) [Amazon]

• Electronics-Salon RPI Relay Board Expansion Module [Amazon]

• Arcity 5V 12V 24V Output Switching Power Supply Unit [Amazon]

• MILAPEAK 8pcs (4 Sets) 8 Positions Dual Row 600V 25A Screw Terminal Strip Blocks with Cover [Amazon]

• 12pcs 7mm 3V-6V-12V-24V-230V/1A Prewired Mini Momentary Push Button [Amazon]

• 5pcs 8mm 3V-4.5V-5V-6V-7.5V-9VDC LED Metal Indicator Light [Amazon]

For my siren build, I used a 7-wire trailer power harness to run from the AF timer box to the siren and connect up:

• 7 Way RV Trailer Light Connector Socket (for the siren) [Amazon]

• 4 FT 7 Pin Trailer Plug Heavy Duty Trailer Wire Extension (for the AF timer) [Amazon]

For assembly:

• Attach the power supply using 2x M2x5 screws to the pad in the back of the box.  The wire pads should face the right side of the box.

• Attach the RPI relay board to the PI, and attach standoffs to the PI and to the relay board (the relay board will stick out past the PI, so you'll need to support it).  That assembly goes in the front right of the box on the smaller pad, with the relays facing the back of the box.

• Attach one of the 8-wire screw terminals to the front left of the box, using the screw holes as a guide.

• Thread each of the buttons, according to color, through the button holes in the lid and secure with their included nuts.  Write to the PI as desired.

• Thread three of the LEDs through the three holes above the plate in the lid, and wire to the PI as desired.  I used blue, orange, and red – blue to indicate power on, orange to indicate when the PI is fully booted, and red to indicate when the siren is sounding.

• Attach the AF-Timer part of the cord through the circular hole in the front and attach it to the 8-wire screw terminals.  Route as desired for your build.

• Attach a 120 volt power cord through the slotted hole on the right, and attach it to the 120 V inputs on the power supply (and anywhere else it needs to go).

• The 5V output of the power supply can go to the PI.  I used 12V for my siren's solenoids, so those and 120 V live went to the three relays on the PI for software control.

Close it all up, and you're good.

Software

For the PI, I programmed custom software to react to the buttons and to drive the relays. You'll need to adjust this according to your build.  The PI is WIFI-enabled as well, so you can use that to control it also.

Source code can be found at:

https://github.com/darkstar62/siren