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------Question for N7803-1CW Please Put your question below------
I am building a small alarm using a ESP32-DEVKITC-V4, a buzzer and some LEDs. I have a 12v power supply (Mean Well EPS-35-12) connected to the buzzer and LEDs using 2N2222a bipolar junction transistors and 4.7K ohm resistors between the GPIOs and the transistor base. I trigger it through Home Assistant and everything works when the ESP32 is powered from USB. I added the N7803-1CW to provide 3.3 VDC power from the 12 V power supply and disconnected the USB power. An ESP32 dev board gnd pin is connected to the 12 V power supply gnd. The DC-DC converter is connected red to +12 V, black to gnd and yellow to the 3V3 pin on the ESP32 dev board. HA does not recognize the ESP32 and the red power LED on the ESP32 dev board cycles flashing bright, then normal, then bright, then normal. I measured the 12V power supply output and it is very slightly over 12 VDC. I measured the DC-DC converter output and it is very slightly over 3.3 VDC. I put very small caps between the dev board 3V3 pin and gnd and between the 5v pin (not used) and gnd to filter noise, but it didn’t make a difference. Can you suggest what I may have done wrong?
Yes, HA does work with the ESP32 and properly control both the buzzer and LED when the ESP32 dev board is connected via USB. I am using ESPHome to develop the interface and controller code. I think that there must be something about the 3.3 V connection that I am not doing correctly. Anything that looks obvious usually isn’t. I am wondering if a 5 V connection would be simplier. I wish I could find out the significance of the dev board LED flash pattern. I have posted on the espressif English forum but am not getting any responses. The espressif doc for the board states that the power LED indicates either a 5 V supply or a USB connection, but I can’t find anything about the flash pattern. Here is my schematic from KiCad. I am not great at this (still learning). The LED has a built in resistor.
@Steven_14444 Pardon me, I missed part of your response. This works properly with HA when the ESP32 dev board is connected via USB and does not work when connected by the DC-DC controller (and the USB disconnected at that time). HA does not recognize the ESP32 when powered by the DC-DC controller.
I can think of a couple of possible issues to consider.
The start-up current of your ESP32 board might exceed the capability of the DC-DC converter.
The ripple voltage on the output of the DC-DC converter (up to 100mV peak-to-peak) might be excessive and causing issues with the board.
Which version of the ESP32-DEVKITC-V4 board do you have, and do you know what the max current draw of that board at start-up is? It’s possible that it is drawing more than the N7803-1CW can source. If so, it will cycle on and off repeatedly as it turns off from an over-current condition, turn back on, and repeats. This may be fast enough that a multimeter might not be able to measure that cycling.
Regarding #2 above, if the ESP32 board is sensitive to that kind of ripple voltage (up to 100mV p-p), then adding a Pi filter to the output to smoothen out the voltage might possibly help.
However, going with a 5V output DC-DC converter of sufficient output current might simplify the issue. The ESP32 board has an on-board linear regulator to regulate down to 3.3V from 5V, and linear regulators are very good at minimizing ripple from passing through from the input. If the ripple voltage is the issue, then this would probably solve that problem.
So, if I’m looking at the correct schematic for the ESP32-DEVKITC-V4, then this should not be happening. The red LED is connected directly to the 5V rail, which is why it indicates either a 5V or USB connection. The ESP32 has no means of making it blink.
The only reason I can imagine it would be flashing is if the N78 is constantly going into protection mode, perhaps due to a short circuit condition? Can you describe the flashing in greater detail? I assume by “normal” you mean off? How fast is it? Is it on more often than off, or vise versa?
What sort of testing equipment to you have at your disposal? I’d start by checking the current consumption at the 3.3V pin…
Thank you both @Matt_Mielke and @David_1528 for the suggestions. The ESP32 startup power supposedly is 300-500 mA, but the N7803 can supply 1A. Response time isn’t listed. The N7803 is described as ‘low noise’, but no specs given. However, I tried an experiment where I brought in 3.3 V to the dev board AND connected a small cap over to gnd to reduce noise. That didn’t help. I also did that on the unused 5 V pin. I am a novice at electronics (elementry college coursework 50 yrs ago) and was overwhelmed by the ESP32 power schematics. However, following that posted by Matt also makes me wonder just what I am seeing! The flash cycle is about once per second. The ‘normal’ is on, about the brightness of when I had it connected to USB. The ‘bright’ is much brighter. I am about to give up and try 5V. First a 5V power supply (I think that I have one). Then, if that works, a 12V to 5V power converter. I would really like to only have 1 power supply in this alarm. I also have several other projects that I want to build that will have similar issues.
I only have a multi-meter, but a friend has a scope and other simple equipment.
Yeah, considering where that LED is located, that really is strange. The only way that could be lit is if current were flowing back through the 3.3V regulator (this can happen with some regulator designs), or if you actually have a wiring problem. It is easy to make little mistakes or accidentally have things shorted together without realizing it (believe me, I’ve done that more times than I’d like to admit).
There is also a possibility that the N7803 isn’t running in a stable manner, particularly if the wire connections between the 12V supply and the N7803 is fairly long or the wires from the N7803 to the ESP32 are long. Using that o-scope might help verify that.
If this is the case, adding some capacitance to the 12V input leads as close as possible to the N7803 might help. This would provide a local reserve of charge near the regulator to draw current from without having to pull it all through the wires from the 12V supply when it demands it. I would add at least 47uF of a low-ESR capacitor and see if that helped.
OK, I got the circuit completely working. A friend suggested pressing the reset button on the ESP32 dev board while the power stabilizes and that works. I guess that the N7803 takes ‘a while’ to stabilize which confuses the ESP32. Oddly enough, the dev board LED is still illuminated with the 3.3 V input.
