TheMonarch

#357 TheMonarch

The Monarch is the third in a series of beautiful electronic "bug" boards from the Boldport Club, Project #18 October 2017.

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Notes

Parts

Ref	Item	Qty
IC1	555 IC timer, TI TLC555CP	1x
IC2	Quad 2-input XOR, TI SN74HC86N	1x
IC3	Octal D-type flip-flop, TI SN74HC273N	1x
-	IC DIP 8 contact socket, TruConnect DS1009-08	1x
-	IC DIP 14 contact socket, TruConnect DS1009-14	1x
-	IC DIP 20 contact socket, TruConnect DS1009-20	1x
LED1-8	5mm clear lens red LEDs, TruOpto OSR5PA5C31C	8x
SW1	Switch, C&K JS202011SCQN	1x
-	CR2032 batter clip, Multicomp BC-2001	1x
C1,2	1µF capacitors, Suntan TS170R1H105MSBFA0R	2x
R1,2,3	10KΩ resistors, Multicomp MCF 0.25W 10K	3x
R4-22	560Ω resistors, Multicomp MCF 0.25W 560	18x
-	20AWG wire	16cm

Circuit

My Take on "How it Works"

The core components:

• a 555 astable timer that is enabled when the "feelers" are touched together, running at around 48 Hz
• 74HC273 D flip-flop, that latches the input (D) to the output (Q) on the rising edge of the clock input
• a 74HC86 quad 2-input XOR

Considering an initial condition of all registers (Q) high:

• XOR Y2 = 1 xor 1 = 0
• XOR Y1 = 1 xor 0 = 1
• XOR Y4 = 1 xor 1 = 0

So on the next 3 clock cycles:

• input D1=0 cascades to Q1,2,3

On the 4th clock cycle, Q4 goes low, XOR Y4 becomes 1, ... and so on.

I wrote a little script to simulate this.

$ ./lfsr.py

Which outputs (for the first 32 steps)..

CLK	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8
0	1	1	1	1	1	1	1	1
1	0	1	1	1	1	1	1	1
2	0	0	1	1	1	1	1	1
3	0	0	0	1	1	1	1	1
4	0	0	0	0	1	1	1	1
5	1	0	0	0	0	1	1	1
6	0	1	0	0	0	0	1	1
7	1	0	1	0	0	0	0	1
8	1	1	0	1	0	0	0	0
9	1	1	1	0	1	0	0	0
10	1	1	1	1	0	1	0	0
11	0	1	1	1	1	0	1	0
12	0	0	1	1	1	1	0	1
13	0	0	0	1	1	1	1	0
14	1	0	0	0	1	1	1	1
15	1	1	0	0	0	1	1	1
16	0	1	1	0	0	0	1	1
17	1	0	1	1	0	0	0	1
18	0	1	0	1	1	0	0	0
19	0	0	1	0	1	1	0	0
20	0	0	0	1	0	1	1	0
21	0	0	0	0	1	0	1	1
22	0	0	0	0	0	1	0	1
23	0	0	0	0	0	0	1	0
24	0	0	0	0	0	0	0	1
25	1	0	0	0	0	0	0	0
26	0	1	0	0	0	0	0	0
27	0	0	1	0	0	0	0	0
28	0	0	0	1	0	0	0	0
29	1	0	0	0	1	0	0	0
30	1	1	0	0	0	1	0	0
31	1	1	1	0	0	0	1	0

The repeating pattern is obvious. This is actually an instance of a linear-feedback shift register (LFSR). Since The Monarch has XOR taps at registers 8, 6, 5, 4, the feedback function can be expressed as x^8 + x^6 + x^5 + x^4 + 1

With that function, it should repeat every 255 cycles. Which it does..

$ ./lfsr.py -1

CLK	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8
0	1	1	1	1	1	1	1	1
1	0	1	1	1	1	1	1	1
2	0	0	1	1	1	1	1	1
...
254	1	1	1	1	1	1	1	0
255	1	1	1	1	1	1	1	1

Recently Julian Ilett delved deep into LFSRs in his inimitable style with "The 10,000 Year Shift Register":

Construction

Here is a quick video of the LED sequencing in action:

All Bugs Together

The Monarch joins The Lady and The Gent in the Boldport Bug series. They are all beautiful boards, so I think mounted together would be nice.

I had an Ikea RIBBA picture frame, discarded the front glass and mounted reflective film at the rear. The bugs are all wired into a 2xAA battery pack with switch on the rear.

Here's a video of the frame:

Credits and References

• Monarch - Boldport product information
• Monarch - in the Boldport shop
• Monarch - OSH files on GitHub
• Monarch - club community site, packed with resources for the project
• 74HC273 datasheet
• LM555 datasheet
• 74HC86 datasheet
• Ikea RIBBA Frame
• LFSR - wikipedia
• ..as mentioned on my blog