I got some bread boards and a kit full of resistors, caps, LEDs, etc. On Amazon, and 3 esp32s (dfRobot boards) from digikey. Very exciting! I already blew an LED (current limiting resistor? Never heard of her!)

  • MyFeetOwnMySoul@lemmy.caOP
    1·
    1 year ago

    Ah ha (great band)! Zener diodes! That was the only component in my kit I was unfamiliar with (aside from the various ICs), very cool tech.

    Another question:I have 5v and 9v vrms, and obviously I need 3.3v; given that a vrm guarantees a fixed voltage regardless of current draw, can I use a downstream resistor to step the voltage down to 3.3v? Or is that also gonna cause problems?

    • dragontamer@lemmy.world
      2·
      1 year ago

      I covered this a bit earlier. Lemme repeat a bit:

      The reason why VRMs are used is because the effective-resistance of real-life circuits change. The ESP32 sometimes draws 150mA when the radio is on (aka: sometimes its resistance is 20 Ohms), other times the ESP32 draws 20mA when idle or even less when asleep. (ie: its resistance changed to 150 Ohms).

      Which resistor can you use to turn a 5V VRM into a 3.3V VRM when the ESP32 is sometimes 20 Ohms, sometimes 150 Ohms? Answer: you can’t. Not with a fixed resistor. You need a device that reacts and changes its resistance to match constantly. Aka: a VRM.

      Only voltage-regulators can solve the voltage regulator problem. You can build a voltage regulator out of transistors, op-amps, or other such devices. (You can build one out of a uC like Arduino even though its really jank… but ADCs exist for a reason and capacitors + inductors do funny things at funny speeds that an Arduino can control).

      Now, there are VRMs that are controlled by simple voltage dividers / aka simple resistors can control a VRM. But really, if you want 3.3V you should get a 3.3V voltage-regulator.

      Alternatively, you get an “adjustable” voltage regulator (really: its a voltage-regulator with a very low set voltage, like 0.6V or something). You then use a voltage-divider (aka: 2x resistors) to control the feedback pin. Its a bit complex but you gain a “user-configurable” voltage by just changing resistors later. For example, the LM317 is nominally a 1.25V voltage regulator, but with the following circuit:

      EDIT: It probably should be noted that the typical LM317 has 2V of dropout. That means 5V can turn into 3V, but not 3.5V (aka: only 1.5V of dropout). To have less dropout, you need a low-dropout voltage regulator.