> I would suggest using a 7809 which drops the voltage to 9V. Someone else > suggested a 7805, and that's not what you want because its output > voltage is 5V which falls far short of the minimum of 8V that you cite. No, I didn't write what output voltage I need, and certainly not that I need 8 V at the output. But now I write that I need 5 V as the signal level. I connect the DCD line to the Arduino Mega 2560 and use the IRremote library. And in reality, I don't even know which voltage regulator is used in my circuit. The circuit is built into a DE-9F connector that I bought 20 years ago as LIRC-compatible home-brew IR-receiver. I used it for a long time on the serial port of multiple mainboards. I can't open it without cutting the heat shrink tubing. And that's why I'm not opening it. Everything I know I read here: https://lirc.org/receivers.html It is written there: "For most standard PC serial ports this will be approximately 10V. IC2 will convert the input voltage to exactly 5V. ... So you should make sure that your serial port delivers at least 8V of output voltage." I need exactly 5 V for Arduino Mega 2560. And I trust that my LIRC-compatible home-brew IR-receiver converts the input voltage to 5 V and I get 5 V as signal level for Arduino Mega 2560. I don't have an oscilloscope to check the signal level. I tested my LIRC-compatible home-brew IR-Receiverwith 12 V supply voltage. It works very well with RC5 remote control and neither IR-receivernor Arduinobroke.