Lesson 2. Two displays

To know whether a factory works well, you have to measure it. In this lesson two displays appear on the base: on the left — how many parts are released into the line, on the right — how many are made (reached the sink). Each display is counted by a pair of CD4029 chips, and button R clears both.

2.1. Idea: what to count

Two numbers describe the whole factory:

released — how many parts went into the line;
made — how many came out finished.

Their difference is the work in progress: the parts that are inside the factory right now — on the belts, in the machines' buffers and being worked on. While the line is healthy, the work in progress stays at one level: as many go in as come out.

2.2. Idea: where the pulses come from

«Released» is counted by the source itself: for every part that leaves it, the OUT leg gives a short pulse. Why not a beam at the source? When the first machine is snowed under, the parts stand on the first belt touching each other, and the beam between them never opens — two parts would merge into one.

«Made» is counted by an IR pair across the last belt — that is how parts are counted on real conveyors too. The emitter always shines (In = VCC), the receiver gives 1 while the beam is whole. A part enters the beam — 0, passes — 1 again. That 0 → 1 edge is the «+1». The last belt runs fast (160 pixels a second), so even two parts in a row go along it with a gap, and the beam has time to open between them.

An IR pair across the last belt: a part blocks the beam — the receiver gives 0; it passes — 1 again. That edge is what the «made» counter counts.

2.3. Idea: the CD4029 is a 4-bit counter

On a rising edge of its CLOCK leg the CD4029 adds 1 (or subtracts). Its legs:

Leg	What it does	Here
CLOCK	edge 0 → 1 — the next count	OUTR / OUTM
UD	1 — up, 0 — down	VCC (up)
BD	1 — binary (0…15), 0 — decimal (0…9)	VCC (binary)
PE	1 — load J4…J1 at once, without a clock	RST (button R)
J4…J1	what to load on PE	GND (0000)
CI	0 — counting allowed	see below
CO	0 — «I am at 15 and about to roll over to 0»	see below
Q4…Q1	the count: Q1 is the low bit	R3…R0 / M3…M0

Button R puts PE = 1 on all four counters: each loads J = 0000, and the displays go to 0.

2.4. Idea: two CD4029 — eight bits

One CD4029 counts only up to 15, and a shift will have 128 parts. So we take two: the low one counts Q1…Q4, the high one the next four bits. The high one must add 1 only when the low one goes from 15 to 0. That is exactly what the low one's CO leg tells: it is 0 while the low one stands at 15. We feed it to the high one's CI:

the low one's CI = 0 (GND) — the low one always counts;
the high one's CI = the low one's CO — the high one counts only on the 15 → 0 step.

Parts	High Q4…Q1	Low Q4…Q1	low CO
14	0000	1110	1
15	0000	1111	0
16	0001	0000	1
17	0001	0001	1

Both CD4029 are clocked by the same signal and switch at the same moment — such a counter is called synchronous. Eight bits — numbers from 0 to 255.

Two CD4029 — eight bits. Both are clocked by the same pulse, but the high one counts only when the low one goes from 15 to 0: its CI is the low one’s CO.

2.5. Idea: a display reads a bus

The counters' outputs are labels R0…R7 («released») and M0…M7 («made»). A display needs no wires: its setting names a bus — R or M — and it reads the labels with that name and the numbers 0…7 by itself and shows the number in decimal.

2.6. Assembly

Import the kit's chips: the file dice-chips.json (the import button in the library). A «Dice» folder appears: CD4029, CD4069, CD4081.
Insert the lesson with Cmd+I on top of lesson 1 (the text is at the end of the lesson). You get: - on the base — an IR pair across the last belt, button R, the «released» display (bus R) and the «made» display (bus M); - outside — four CD4029; - the source's OUT leg gets the label OUTR.

2.7. Check

Switch the power on and press R — both displays show 0.
The left display grows once a second, the right one starts to grow after about 13 seconds — that is a part's way through the line.
After that both grow alike, the right one about 13 behind.

What you look at	What you see
left display (R)	= the number on the source
right display (M)	= the number in the sink, or 1 more
difference	about 13 and does not change

The right display may be 1 ahead of the sink: a part has already passed the beam but has not reached the sink yet. If the left display is less than the number on the source, R was pressed after the first parts had already left. In lesson 3 START appears, and the order becomes right: power → R → START.

Lesson 2 insert (`Cmd+I`)

# Lesson 2 — two counters. "Released": the source gives a short OUT pulse for every part it lets out.# "Made": an IR pair across the last belt — a part passes, the beam is whole again (0 -> 1), the counter adds one.# Each counter is two CD4029 in binary mode (BD = 1): 8 bits, 0...255. R — reset (PE loads J = 0000).# Insert on top of lesson 1 (needs the chip file dice-chips.json).reconnect(src.OUT = OUTR)irtx txM{channel=1, ang=90}(In=VCC)at(txM, B, 710, 120)irrx rxM{channel=1, ang=90}(Out=OUTM)at(rxM, B, 690, 260)button rst{label="R"}(RST)at(rst, B, 140, 290)display shR{busSource=R}at(shR, B, 300, 290)display shM{busSource=M}at(shM, B, 460, 290)"TI CD4029B"(CLOCK=OUTR, UD=VCC, BD=VCC, PE=RST, CI=GND, J1=GND, J2=GND, J3=GND, J4=GND, Q1=R0, Q2=R1, Q3=R2, Q4=R3, CO=COR)"TI CD4029B"(CLOCK=OUTR, UD=VCC, BD=VCC, PE=RST, CI=COR, J1=GND, J2=GND, J3=GND, J4=GND, Q1=R4, Q2=R5, Q3=R6, Q4=R7)"TI CD4029B"(CLOCK=OUTM, UD=VCC, BD=VCC, PE=RST, CI=GND, J1=GND, J2=GND, J3=GND, J4=GND, Q1=M0, Q2=M1, Q3=M2, Q4=M3, CO=COM)"TI CD4029B"(CLOCK=OUTM, UD=VCC, BD=VCC, PE=RST, CI=COM, J1=GND, J2=GND, J3=GND, J4=GND, Q1=M4, Q2=M5, Q3=M6, Q4=M7)

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