20250715 The MkVII’s Blinking Lights

20250715 The MkVII’s Blinking Lights

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Before I start, I am going to repeat this again. I know I have explained about this before but before I can move to the actual point, I need to explain this again. The one main thing that got me attracted to the MkVII Tricorder was its blinking lights. It was the main reason I persevered with my Electronics Degree when I realised I really wanted to go into Industrial Design.

The Heart of the Blinkies

The lights in the Tricorder blinks in a 4-step sequence on repeat, which can be replicated with modifying a 555/4017 circuit. This is, to me, the Heart of most TNG props that requires ‘Running lights’. I did not realise the potential of that circuit until I put 2 and 2 together after seeing the Tricorder in action, read some Datasheets and also, thanks to some Forums, kicked my lazy butt. The modification is to connect the pin#10 to pin#15 in the 4017 IC. This makes the 4017 decade counter count up to four and on the fifth step, resets itself without any delay. Otherwise, the 4017 on a normal setup would count up to ten before it resets itself.

20250715 The MkVII’s Blinking Lights

From the image above, there are four green indicators on the left of the Tricorder’s screen and they are labeled (from top to bottom) Alpha, Beta, Gamma and Delta. Depending on how they are wired for the show, the sequence can either start from the top or from the bottom. It is just the matter of wiring the LEDs. Sometimes you will notice that the speed of the sequence varies and that can be done by varying the resistance of the 555 timer. I suppose the said timer is crucial because how long the lights come one and goes out, depends on the two resistors and one capacitor.

This is an example of a typical 555/4017 circuit. In my design, I would have omitted 1N4148 Diode, the BC547 NPN Transistor, and practically all five components on the left before the 2 resistors and the capacitor.

Anyway, it is easy to just use the 555/4017 circuit to light up the whole Prop. But when I looked at the video below, the sequence does not support the theory. The sequence of the Alpha, Beta, Gamma, Delta and the rightmost three LEDs are not in sync.

Look at the sequence from 00:18 to 00:35. The timing of each lit four LEDs on the left does not ‘sync’ with the three LEDs on the right.
(Screen Used MkVII Tricorder courtesy of Popology101.)

To show you what I mean, look at the sample chart below. Let’s say, when the ALPHA LED is on at positions K2 to L2 (R2-S2, X2-Y2, AD2-AE2), LED #2 (A8) should be lit. But it is not so as if you look at the three LED sequence in rows 7,8,9 each time these LEDs light up, they are not sychronised with the LEDs in rows 2, 3, 4 & 5. Whether this is true or not I cannot confirm it since my method of sampling is not accurate; it was just me pressing the spacebar at the right interval as best as I can.

I took a simple mapping sample (G-AE) of the sequence and from there, it is likely there are two independent 555/4017 circuits in there, with the lower 3 LEDs sequencing slightly faster.
Let’s separate the upper 4 LEDs (yellow) and the bottom 3 LEDs (blue). As the LED sequences from G to AE, each of the LEDs are lighting up in their own sequence and timing. If you concentrate on the yellow, all is well but the blue, even it is sequencing correctly, are moving slightly faster. The same can be said if you concentrate on the blue instead, where the yellow seems to be out of sync.
Deciding on the which sequence to emulate is not easy. If I follow the yellow, I have a problem where, for example, the LED#1 would not light up the same. If I used the orange sequence, the bottom LEDs (blue) are still out of sync. But do note some LEDs stay lit longer such as GAMMA (H4:I4, U4:V4, AA4:AB4) and ALPHA (K2:L2, R2:S2, X2:Y2, AD2:AE2). This could be due to my hitting the Play/Pause inaccurately. If I had more microcontroller ports (say, seven) I would be able to replicate the whole sequence and give it that non-sync sequence. But in reality, only have four ports and that is it. Caught myself from going too detailed for a simple concept because in the end, there is not much difference.
But hey, since each MkVII’s sequence is not the same, I can technically do my own. So, for the time being, I am just going to follow the sequence (yellow) and not only that, this will save on microcontroller ports and simplify traces in the PCB. A microcontroller is ideal because, the 555/4017 circuit cannot do reverse sequence.

Posted in A Piscean Works Blog.

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