Lesson 3. Release at Herbie's rhythm

Herbie makes a part in 2 seconds, and we release a part every second. Half of the parts add nothing to the output — they only stand in the queue in front of Herbie, taking up belts and buffers. Goldratt calls the cure subordinating everything to the constraint — working at the rhythm of the slowest link. In this lesson we build a rhythm switch: a part a second or a part every 2 seconds.

3.1. Idea: a frequency divider on one flip-flop

We need a signal that rises half as often as REL. A CD4013 D flip-flop does this if its D input is connected to its own inverted output QN: every CL edge stores the opposite value — the flip-flop flips.

  • CL1 = REL — every release pulse;
  • D1 = QN1 — flip on every edge;
  • Q1 = HALF — changes once a second, rises once every 2 seconds;
  • R1 = R — button R sets the flip-flop to 0.
RELHALFthe flip-flop flips on every REL edge: D1 = QN1HALF rises once every 2 seconds: Herbie’s rhythm
A frequency divider on one D flip-flop of the CD4013: the output is half as frequent as the input.

3.2. Idea: a selector — the CD4019

The CD4019 has four «one of two» selectors. Each section computes D = A · KA + B · KB: it passes A if KA = 1, and B if KB = 1. We take one section:

  • A1 = REL (rhythm 1 s), KA = NSLOW;
  • B1 = HALF (rhythm 2 s), KB = SLOW;
  • D1 = RELS — what goes to the source.

SLOW is a switch, NSLOW = NOT SLOW — a free inverter of the FL-01 CD4069 (input B, output H). Switch off — REL passes, on — HALF.

one section of the CD4019RELHALFSLOWCD4069NSLOWRELSsourceRELEASERELS = REL · NOT SLOW + HALF · SLOW
The rhythm switch: the SLOW toggle picks what goes to the source — every second (REL) or every 2 seconds (HALF).

The end of the shift still works: R7 closes REL, and without REL the divider does not flip either.

3.3. Assembly

Insert the lesson with Cmd+I on top of lesson 2. You get:

  • on the base — the SLOW switch;
  • outside — a CD4013 and a CD4019;
  • the free inverter of the FL-01 CD4069: input B → SLOW, output H → NSLOW;
  • the source's RELEASE leg is reconnected from REL to RELS.

3.4. Check

Two shifts, the probe on Herbie (R, then S, S). Look in the third minute.

What you look atSLOW off (1 s)SLOW on (2 s)
«made»a part every 2 secondsthe same
differenceabout 20about 7
buffers of 1–3fullalmost empty
display I on Herbie00
040801201602002402800510152025seconds from STARTwork in progress, partsrhythm 1 sHerbie’s rhythm, 2 s«made» in both — the same
Work in progress during the shift (our factory, test bench). In Herbie’s rhythm — three times less, while «made» grows exactly the same in both rhythms.

The factory makes exactly as much, but holds three times fewer parts inside. The extra parts were released for nothing: Herbie would not have had time for them anyway.

Lesson 3 insert (Cmd+I)

# Lesson 3 — release to Herbie's rhythm. Insert on top of lesson 2.# HALF = REL divided by 2: a CD4013 flip-flop flips on every REL (D1 = QN1) — one rising edge every 2 seconds.# CD4019 picks the rhythm: RELS = REL · NSLOW + HALF · SLOW. NSLOW — a free inverter of the FL-01 CD4069.# The source now listens to RELS.input slow(SLOW)at(slow, B, 40, 350)reconnect(NDONE.B = SLOW)reconnect(NDONE.H = NSLOW)"TI CD4013B"(CL1=REL, D1=HN, Q1=HALF, QN1=HN, R1=RST, S1=GND, CL2=GND, D2=GND, R2=GND, S2=GND)"TI CD4019B"(A1=REL, B1=HALF, KA=NSLOW, KB=SLOW, D1=RELS, A2=GND, A3=GND, A4=GND, B2=GND, B3=GND, B4=GND)reconnect(src.RELEASE = RELS)

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