# #357 TheMonarch

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

## 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

### 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: