[Dr_C]

This project has reached the point where the backplanes have been assembled for an 11-digits-in-a-row numerical read-out.

The revised sequence is:

2 white digits then
2 green digits then
5 red digits then
a final 2 green digits

The 2 white digits will always show the IDs of cars traversing the speed trap.

The 5 green digits will either show speed trap transit time, transit speed or latest lap time.

At present I am identifying the correct series resistors for the white, green and red segments when driven by a 12V supply. Also, since the decimal points have different LED configurations these also require correct identification of the series resistance which will provide a matching of intensity.

The three colours of LED digits are shown below:

   

Note, the red digit looks red to the human eye but captures more orange-like with my iphone camera. In ‘reality’ it is red… honest.

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[Dr_C]

The first photo shows three of the ‘modular’ 4 inch 7 segment displays as required for the speed trap project.

The module on the right has the data digital inputs and the 15V power supply input.

The data digital inputs are wired via a quad opto isolator followed by digital inverters.

The 15V input feeds into a 12V regulator which drives the common anode LED display modules. The 12V regulator in turn feeds into a 5V regulator which drives the digital logic.

The other two modules shown don’t require this additional circuitry.

   

This second photo shows the three modules connected together via their male and female headers.

   

The third photo shows the same three display modules displaying ‘888’ as generated by a nearby microcontroller.

   

Next, some additional display modules to be added and some track sensors to drive the timing firmware inside the microcontroller.

:)

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[Dr_C]

In this case, the bespoke PCB design helps to keep hook-up wiring to a minimum … we could call this approach ‘neat-and-tidy’ [1].

This is important when the project requires a daisy-chaining of 11 of these modules.

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[1] Quote from: Vengeance Most Foul, Aardman Animations (2024).

[Dr_C]

As explained earlier, this approach is highly modular with only the first display module in the sequence requiring the opto-isolation on input data channels (of which there are 3) and the 12V and 5V LDO regulators.

So the current version has the sequence…

WWYGRRRRRGY

W=White
Y=Yellow
G=Green
R=Red

and so a total of 11 modules in a row and circa 1 metre wide.

This gives two useful operating modes:

First as a speed trap showing either

• car ID plus speed
  
• or car ID plus lap time
  (in each case two white digits followed by five red digits with the latter with numerical format xx.xxx)
  

Then, second, as a very large sized mirror of the start/finish gantry…

• five red lights towards the centre
  
• with one green light either side
  
• then with one yellow light further out either side
  (Here lights in each case are square patterns formed by the upper-most four segments of the seven segment displays).
  

This is a indeed a very large mirror of the start/finish gantry!

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