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Without a program counter, how does a jukebox remember the next step?

Release the jukebox button and the record keeps moving. Follow the holding circuit, then compare a pinball reset with a furnace pressure switch to find where state lives and what lets a sequence advance.

Questions in this reading · 3
  1. What keeps the jukebox going after the finger lifts?
  2. What must pinball forget before the next ball?
  3. After a start command, which feedback unlocks the next step?

What keeps the jukebox going after the finger lifts?

A brief button press closes a relay. A contact then supplies current to the coil, holding the state after the finger lifts. A separate condition must interrupt the path. On the jukebox that condition can come from a transfer switch moved by the mechanism. On a diagram, trace both the holding circuit and the path that opens when the record reaches position.

Passages and timestamps · 2
Self-latching circuits with interrupts.
The Computer-free Automation of a Jukebox (Electromechanics) · ▶ 8:06–8:09
it’s latched through this, the transfer switch.
The Computer-free Automation of a Jukebox (Electromechanics) · ▶ 12:27–12:31

What must pinball forget before the next ball?

A jukebox record change and a pinball score both expand a short input into a sequence of actions. A score motor and relays can move the pinball sequence forward, but the next ball also requires a selective reset. Imagine starting a new ball just after a special bonus was active. A test beginning only at power-on could miss state leaking across that boundary.

Passages and timestamps · 3
with a few relays and a wacky contraption called the score motor
The step-by-step, mechanical logic of old pinball machines · ▶ 0:16–0:20
it also needs to reset any of the relays that might have been triggered in the last ball
The step-by-step, mechanical logic of old pinball machines · ▶ 29:14–29:19
Self-latching circuits with interrupts.
The Computer-free Automation of a Jukebox (Electromechanics) · ▶ 8:06–8:09

After a start command, which feedback unlocks the next step?

A furnace powers its inducer and waits for a pressure change. A separate temperature switch watches for overheating. The jukebox waits for a position change; the furnace waits for a consequence of airflow. Draw “command sent” and “physical response observed” as separate states, then ask whether a missing response could let the system advance anyway.

Passages and timestamps · 3
looks for the output from this pressure switch to change.
Forced-air Furnaces: The What, Why, and How · ▶ 13:40–13:47
it’s designed to protect against overheating.
Forced-air Furnaces: The What, Why, and How · ▶ 17:59–18:04
it’s latched through this, the transfer switch.
The Computer-free Automation of a Jukebox (Electromechanics) · ▶ 12:27–12:31

Try it on your own example

Draw three steps after releasing an appliance button. Which depends on sustained current, which on mechanical position, and which must wait for a change outside the controller?