This control board is from a mini-split heat pump. It sits on the outside of the unit and receives signals from a remote control. It's from this discussion here.

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It's a single-sided board - am I getting the schematic correct, and is this typical for an infrared sensor e.g. used with remotes?

The brown and orange aren't clearly identified. If those were accidentally swapped will they just light the wrong light? Or could something worse happen?


simulate this circuit – Schematic created using CircuitLab

Bonus questions: Why two capacitors? What's the point of the resistor (is that a resistor?) in series with red/supply?

  • \$\begingroup\$ Bend the three-terminal device away from the board to get the part number on its flat face. LAMP1 and 2 should probably use the LED symbol. \$\endgroup\$
    – Transistor
    Commented Jan 14, 2023 at 7:46

2 Answers 2


The two caps provide good supply bypass. The electrolytic does the low frequencies and the ceramic handles the high frequencies.

R1 is an idiot resistor. Imagine if U1 fails short circuit -- R1 keeps currents safe.

  • 2
    \$\begingroup\$ R1 could also be for noise filtering - R1 and C1/C2 form a low pass filter for the supply. \$\endgroup\$
    – jpa
    Commented Jan 14, 2023 at 12:43
  • 2
    \$\begingroup\$ R1 might also prevent destruction of U1 if cables get mixed up and power is applied in the wrong polarity. \$\endgroup\$ Commented Jan 14, 2023 at 13:03

Chances are the three-terminal component is an IR receiver.
Either there is a hole/window in the casing, or that would need to be somewhat transparent to IR.


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