I just wanted to ask a quick question. Mostly with the Arduino with buttons etc. you have to use a pull-up or pull-down resistor for the signal to be received correctly.

How does it look like when I want to send a analog control signal/voltage between 2 ICs (DAC and LED-Driver, "PT-4115").

Do I have to place a resistor in between those 2 for current limitation (schematic 2) or perhaps also one to ground (schematic 3) or both variants together (schematic 2 and 3)?

If so, does it have to be high/low resistance?

Here's a quick schematic attached: enter image description here

edit: I cant use a PWM control signal, therefore needing to control the LED driver by analog voltage from a DAC.

  • \$\begingroup\$ 2and 3. You want #2 so that when reset, the dac may not be actively driving the pin until it is configured. #3 just in case you want some current limiting. Make it 100R at a guess. \$\endgroup\$
    – Kartman
    Aug 6, 2021 at 13:28

1 Answer 1


A DAC normally outputs a voltage so, if your receiver IC is up close and it shares the same 0 volts line then no need for a resistor in normal circumstances. You might choose to use a series resistor if the DAC can output a voltage that is beyond the input supply voltage for the receiver though. That resistor would be to protect the receiver IC.

If the DAC and receiver are on separate power supplies then all manner of different configurations might be needed to get what you really want. For instance, different power supplies (unshared 0 volts but galvanically linked) will require a differential input at the receiver. That involves 4 resistors.

Galvanically isolated systems may require a much more sophisticated means of receiving such as isolated signal amplifiers of course.

If your system runs on a common 0 volts then I would be tempted to put a series resistor close to your receiver input and maybe a high-value pull-down resistor from the signal line to ground. That second resistor would serve to return the signal to a 0 volt level should the two parts (DAC and receiver) be disconnected.

Mostly with the Arduino with buttons etc. you have to use a pull-up or pull-down resistor for the signal to be received correctly.

That's because buttons are totally passive circuit elements.

  • \$\begingroup\$ Thank you both very much! Basically you both confirmed my thoughts. Both ICs are on the same 0V line. The max input rating is 6V for the LED driver input signal and the DAC max. output is 5.5V. Therefore, no resistance would be needed, but I could add one for safety reasons, but really not absolutely necessary. Another question: Does the "R_dim" value represent the internal resisitor for the input pin or is it for something else? -> led-stuebchen.de/download/PT4115E.pdf (page 4) \$\endgroup\$
    – Dakalaom
    Aug 6, 2021 at 13:43
  • \$\begingroup\$ @Dakalaom it looks like an internal 200 kohm resistor to me. \$\endgroup\$
    – Andy aka
    Aug 6, 2021 at 13:49

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