Lesson 1. The CD4013 D flip-flop

After this lesson the library has the CD4013 chip — two D flip-flops, and the canvas has the first part of the parking sensor: the divider the whole device steps on. We try the flip-flop with switches and a button.

1.1. Idea: remember at a moment

The parking sensor polls its sensors in turn, step by step. The steps need a clock, and the clock needs an element that remembers the value at the moment the clock changes from 0 to 1 (the edge) and holds it until the next edge, whatever the input does. This is a D flip-flop: input D (data), clock CL, output Q.

• an edge of CL — Q becomes equal to D;
• the rest of the time Q holds, and D can change as it likes;
• S = 1 — 1 at once, R = 1 — 0 at once, without a clock.

1.2. Idea: master and slave

Inside are two latches in a row. The first (the master) lets D through while CL = 0 and closes when CL = 1. The second (the slave) does the opposite: it opens when CL = 1 and takes what the master has locked. Together they are never open all the way through, so Q changes only on the edge.

Each latch is two NANDs and two TG switches: the data switch and the feedback switch. A switch is a pair of transistors, nmos + pmos; it closes the wire when N = 1 and P = 0. The switches are driven by cln = NOT CL and clp = NOT cln — always opposite: when one switch of a latch is closed, the other is open.

1.3. Idea: weak feedback

For the moment the clock switches, cln and clp are both "halfway", and both switches of a latch are closed: the input meets the output of the feedback. In a real chip the feedback transistors are small — the input wins. Here this is a Resistor (weak) in front of the feedback switch: a "weak wire" that gives way to a real output.

Capacitor (hold) on nodes a and b is their capacitance: it holds the value when both switches are open for a moment.

1.4. Idea: divide by 2

If QN is fed back to D, on every edge the flip-flop writes its own inverted value: Q changes every other clock. A 60 Hz generator turns into 30 Hz — this is the step of polling the parking sensor's sensors.

1.5. Build

A new project. You need the gates NOT and NAND — from lesson 0 or any kit of the series.

Step 1. Chip TG — a switch on a pair of transistors

If TG is already in the library (from the "Visitor Counter" kit — inside the CD4511), skip this step.

A switch as on the TI drawings: nmos and pmos side by side, both connect A to B. nmos conducts at N = 1, pmos — at P = 0. They are always driven by a pair of opposite signals: N = 1 and P = 0 — the switch is closed, N = 0 and P = 1 — open. Transistor: gate, drain, source.

Ctrl+G → name TG. Legs: inputs A, N, P; outputs B.

Step 2. Chip FF4013 — CD4013 D flip-flop (master and slave)

The whole circuit as one drawing — above, in the "Idea" (and in the file ff4013-schema.html). Build order: the inverters R, S, CL; the master — the data switch, two NANDs, the feedback switch with a resistor, cap on node a; the slave — the same; four inverters for the outputs. Resistor (weak) and Capacitor (hold) — from the palette. On the switches watch where N and P go: on the master data switch N = cln, on the master → slave switch — the other way round, N = clp.

Ctrl+G → name FF4013. Legs: inputs D, CL, S, R; outputs Q, QN.

Step 3. Chip CD4013 — 2 × D flip-flop

Package pins from the TI datasheet: 1 Q1, 2 QN1, 3 CLOCK1, 4 RESET1, 5 D1, 6 SET1, 8 SET2, 9 D2, 10 RESET2, 11 CLOCK2, 12 QN2, 13 Q2; 7 — VSS (ground), 14 — VDD (power) — our power is shared, so these pins are not there. Inside — two FF4013: the first on the pins with the digit 1, the second — with the digit 2.

Ctrl+G → name CD4013. Legs: inputs D1, CLOCK1, SET1, RESET1, D2, CLOCK2, SET2, RESET2; outputs Q1, QN1, Q2, QN2.

Step 4. Probe: switches, the Clock button, lamps

Button (momentary) — caption "Clock" (double-click the button). The second flip-flop of the package is not needed in the probe — its inputs go to GND.

Step 5. Probe lamps

Step 6. Parking sensor: generator, Reset, divide-by-2

This is the first part of the parking sensor — it stays until the end of the kit. Clock — click the body up to 60Hz. The button — caption "Reset". The output QN1 (C30N) is fed back to D1: on every edge of CK60 the flip-flop writes its own inverted value, and C30 changes every other clock — 30 times a second.

Step 7. Divider lamps

1.6. Check

D flip-flop probe (switches D, S, R — at 0):

1. First R = 1 and back to 0 — Q goes out, QN lights up. At power-on the flip-flop holds whatever it caught; R sets it to 0.
2. Set D = 1 — Q does not change: a D flip-flop listens to its input only on the clock edge.
3. Press Clock — Q lights up, QN goes out: D was written on the edge.
4. Hold Clock pressed and switch D — Q stays. Only the moment of pressing writes (the CL edge 0 → 1), not the pressed state.
5. D = 0, let go and press Clock again — Q goes out.
6. S = 1 — Q lights up at once, without a clock; set S = 0 back — Q holds. R = 1 — Q goes out at once; set R = 0 back.

Divider:

1. At 60Hz the lamps CK60 and C30 blink faster than the eye can see — they seem lit at half strength.
2. Click the generator body up to 1Hz (through 4kHz … MAX): CK60 blinks once a second, and C30 changes each time CK60 lights up — lit for a second, off for a second. Half the frequency.
3. Hold Reset — C30 goes out and stays, the clocks have no effect.
4. Set the generator back to 60Hz (1Hz → 2Hz → 10Hz → 60Hz) — the parking sensor needs it.

Keep the probe until lesson 2 — there you can delete it. Do not touch the divider: the whole parking sensor steps on it.

Lesson 1 paste (Cmd+I)

You need the gates NOT, NAND (lesson 0). If TG is already in the library, delete its block from the paste.

# Lesson 1 — CD4013B: a D flip-flop on TG switches (master and slave), a 2 × D flip-flop chip; the parking sensor 60 → 30 Hz divider.# Paste: Cmd+I into a new project with the NOT and NAND gates (lesson 0). chip TG {  portIn(A)  portIn(N)  portIn(P)  portOut(B)  nmos(N, A, B)  pmos(P, A, B)} chip FF4013 {  portIn(D)  portIn(CL)  portIn(S)  portIn(R)  portOut(Q)  portOut(QN)  NOT(R, nr)  NOT(S, ns)  NOT(CL, cln)  NOT(cln, clp)  TG(A=D, N=cln, P=clp, B=a)  NAND(nr, a, m1)  NAND(m1, ns, m2)  TG(A=a, N=clp, P=cln, B=m2w)  resistor(m2w, m2)  cap(a)  TG(A=m1, N=clp, P=cln, B=b)  NAND(b, ns, s1)  NAND(nr, s1, s2)  TG(A=b, N=cln, P=clp, B=s2w)  resistor(s2w, s2)  cap(b)  NOT(s1, q1)  NOT(q1, Q)  NOT(b, qn1)  NOT(qn1, QN)} chip CD4013 {  portIn(D1)  portIn(CLOCK1)  portIn(SET1)  portIn(RESET1)  portIn(D2)  portIn(CLOCK2)  portIn(SET2)  portIn(RESET2)  portOut(Q1)  portOut(QN1)  portOut(Q2)  portOut(QN2)  FF4013(D=D1, CL=CLOCK1, S=SET1, R=RESET1, Q=Q1, QN=QN1)  FF4013(D=D2, CL=CLOCK2, S=SET2, R=RESET2, Q=Q2, QN=QN2)} power(VCC)ground(GND)input(D)input(S)input(R)button{label="Clock"}(CL)CD4013(D1=D, CLOCK1=CL, SET1=S, RESET1=R, D2=GND, CLOCK2=GND, SET2=GND, RESET2=GND, Q1=Q, QN1=QN)led(CL)led(Q)led(QN)clock{rt=60}(CK60)button{label="Reset"}(RESET)CD4013(D1=C30N, CLOCK1=CK60, RESET1=RESET, SET1=GND, D2=GND, CLOCK2=GND, SET2=GND, RESET2=GND, Q1=C30, QN1=C30N)led(CK60)led(C30)