Timeline for How do I find out the maximum current through VIN on a NodeMCU board?
Current License: CC BY-SA 4.0
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| Oct 9, 2021 at 18:48 | comment | added | rattlesnake | Oh, and by the way, reminder if you want to add your findings for the v3 NodeMCU to your previous answer that I found: arduino.stackexchange.com/a/51878 (I couldn't comment there because my reputation is too low.) | |
| Oct 8, 2021 at 15:05 | vote | accept | rattlesnake | ||
| Oct 8, 2021 at 15:05 | comment | added | rattlesnake | Yes, I think I'm not going to look further into it at this point. :) Everything works so far. Thank you very much for your help | |
| Oct 5, 2021 at 20:39 | comment | added | Majenko | @rattlesnake Maybe these diodes are dodgy pieces of spit then, as the circuit says that shouldn't work, if the diodes were behaving as they should. | |
| Oct 5, 2021 at 17:42 | comment | added | rattlesnake | I'm sorry to say but it seems like VIN does indeed work as an output: I connected a 10 kΩ resistor (to limit current to a minimum) and a white LED in series between VIN/VU to GND on the NodeMCU. With both VIN, as well as VU, the LED is on. The NodeMCU is powered by USB from my laptop. | |
| Oct 5, 2021 at 17:07 | comment | added | Majenko | @rattlesnake Yep, that's correct. That diode is working fine. You may be measuring 5V on VIN because there's no load and it's just floating. Maybe try powering something small from it and see if it works. The other diode, though, is short circuited. Either because the diode is dead (they usually fail short) or there is a defect in the PCB. | |
| Oct 5, 2021 at 16:56 | comment | added | rattlesnake | Yes, I can see the stripe with a magnifying lens: i.sstatic.net/5Adnr.jpg I hope the photo is good enough. I measure 233 with red left side (towards the outside) and black right side (towards the inside of the board). Isn't that what you said? | |
| Oct 5, 2021 at 16:17 | comment | added | Majenko | With the diode near VIN which way round are the probes when you read 233? It should be red towards the outside and black towards the inside of the board. The other diode sounds broken or short circuited. 233 sounds correct though - 233mV is about the same as I measured and is typical for a small schottky diode. If you peer closely at the diodes you should see a stripe at one end, which is the cathode (where the black probe goes for it to read right). | |
| Oct 5, 2021 at 16:13 | comment | added | rattlesnake | Well, this is interesting. I do have a digital multimeter. However, it is a very cheap one. It does have a diode test program though. I have never used that before. Can I used it while the diodes are soldered onto the board? On the diode closer to VIN I read 233 in one direction and 1. in the other direction. (Not 1, but 1. which mean infinite for the resistor test program.) For the other diode closer to the edge, I measure 002 or 003 in both directions. So... no idea what that means, but it doesn't make any sense to me. | |
| Oct 5, 2021 at 15:53 | comment | added | Majenko | ...from the USB power, the upper going left to right from the VIN pin. From there the 5V goes to the input of the LM1117 voltage regulator. | |
| Oct 5, 2021 at 15:52 | comment | added | Majenko | @rattlesnake If you have a DMM it should have a diode test mode. It should tell you the forward voltage of the diode. In one orientation it should give you abou 0.25V. In the other it should read open circuit. The diode in question is the one closest to the pins. If you're interested the copper traces can be viewed here: cloud.majenko.co.uk/index.php/s/ewCn6JmYdWWglRj The two diodes are in the bottom left - you can just make out the pads in silver above the bottom left mounting hole. You can see both the diodes connecting the power to the 5V rail - the lower one going right to left... | |
| Oct 5, 2021 at 15:42 | comment | added | rattlesnake | Hmm, no idea what to tell you. The board is basically new, I haven't done anything with it so far. I also read 2 to 3 ohm resistance between VIN and VU in both directions. I think if there would be a diode installed like in your schematic, that also shouldn't be the case. I cannot explain my readings. Is there anything I can do? Which part would be the diode in question? Maybe I can test something there? My equipment is very limited though. :( | |
| Oct 5, 2021 at 14:42 | comment | added | Majenko | The only way you can get power out of VIN is if the diode is faulty or installed backwards. That board is identical to the one I've torn down. I am half way through a full reverse engineering of the circuit at the moment. | |
| Oct 5, 2021 at 13:24 | comment | added | rattlesnake | Huh... First of all: thanks for looking into it. However, second of all, I don't understand how this is possible. i.sstatic.net/6NKYn.png This is exactly how my board looks like. Maybe there are different NodeMCU v3? In your schematic, shouldn't I measure 0 V on VIN because it's against the diode direction? But when I connect USB and measure from VIN to GND pins, I read 5 V. (I get 5 V as well from VU to GND, by the way.) Again, thanks for you help :) | |
| Oct 3, 2021 at 15:08 | history | answered | Majenko | CC BY-SA 4.0 |