[arghwhat]

The example toaster has 2 toast slots 3 heating elements (EDIT: Technically 4, as the last element is split into two: RL3 and RL4).

Relay 2, activated when the "bagel" light is lit through the gate of Q2, disconnects neutral from heating element 2 (the one in between slot 1 and 2) and 1 (the one on the outside of slot 2).

This means that there is only power to the outside heating element of slot 1, allowing you to toast only one side of a bread or bagel.

[sgarland]

Then what is RL4? If it were just a resistor for a voltage divider, I’d think it might be labeled differently than the other three.

[arghwhat]

RL3 and RL4 are both heating elements in slot 1 - likely just one heating element with a tap somewhere - that indeed acts like a voltage divider.

The power to the circuit flows from in between those heating elements, through a single rectifier (D1), through a 1W resister (R1), before being clamped to 5.1V by a zener (VZ1). The use of the heating element as a voltage divider is just to get closer to the target voltage (<15V considering the rating of C1), using the fact that a heating element is just a resistor with an enormous power rating. No one cares about the power efficiency of a toaster control circuit.

However, the schematic is missing a connection to VCC from the 5V rail it created - it only connects to the high side of the mains relay/toast magnet as well as the bagel button. It was supposed to connect to VCC, which in that schematic is only connected as to the clock circuit.

(I was not using the RL numbers when I numbered the heating elements in my previous comment originally - my bad. I updated the comment.)

[sgarland]

Thank you, makes sense.