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I have a small circuit with an ESP8266, a DS18B20 temperature sensor and a DHT22. I prototyped everything on a breadboard, and it worked fine. I then moved to soldering everything. My input Vcc is 5v, so I am using it to power the DHT22 and the DS18B20, and the same 5V are also going to the LM1117. Problem is, the LM1117 outputs just 0.65V instead of 3.3V, which is too low to power the ESP8266. I also tried to unsolder everything and just leave the LM1117 alone, and it still outputs 0.65V. Moreover, I changed the LM1117 with another one to check whether it was a malfunction, but it didn't solved the problem.

Any idea on how can I investigate this issue? Where is it possible that I am losing so much voltage?

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    \$\begingroup\$ Do you have the required decoupling capacitors at the input and output of the LM1117 in place ? Did you check that the LM1117's input is getting 5 V ? 0.65 V smells like a diode voltage so re-check all connections to make sure you did not mix them up. \$\endgroup\$
    – Bimpelrekkie
    Commented May 18, 2016 at 9:08
  • \$\begingroup\$ Hi, no I do not have any capacitor. I have others LM1117 working like this, so I didn't checked about this. Yes, the input is 5 V so this is fine. I re-did all the connections two times but I am still getting the same problem. \$\endgroup\$
    – lbedogni
    Commented May 18, 2016 at 9:14
  • \$\begingroup\$ How should anybody here know what the differences between the breadboard and the soldered circuit are? There is unlikely to be an answer such as "this symptom is typical when you've accidentally exchanged pins 5 and 23", so you have to give more information about the actual circuit. \$\endgroup\$
    – CL.
    Commented May 18, 2016 at 9:32
  • \$\begingroup\$ Hi CL., I know this. I am just asking whether there could be some common problems, since as I said the problem is still visible even wehn I only connect the 5V and GND to lm1117 and measure the Vout, which is 0.65V. \$\endgroup\$
    – lbedogni
    Commented May 18, 2016 at 9:35

2 Answers 2

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I'm pretty sure you just didn't connect it properly. Verify pins:

  1. GND
  2. Output (pin 2 is also connected with the metal tab)
  3. Input

If you replaced it and got exactly the same results the connections are the most probable reason, because if you by mistake bought the adjustable variant of LM1117, I think it would output 1.25V. Also it would possibly be useful if you told us if the part heats up.

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  • \$\begingroup\$ Ok, in fact it was not connected properly. Now it is, and it outputs 1.6v, but still not the 3.3 I am looking for. I also disconnected everything to check whether there was a problem with other cables, but it still outputs 1.6. \$\endgroup\$
    – lbedogni
    Commented May 20, 2016 at 8:18
  • \$\begingroup\$ Been there, done that :D Did you try a new one? It's possible that you fried it by connecting it the wrong way. \$\endgroup\$
    – Adam Czapski
    Commented May 20, 2016 at 8:20
  • \$\begingroup\$ Yes I tried, now it outputs 1.2. \$\endgroup\$
    – lbedogni
    Commented May 20, 2016 at 8:47
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I am sure you are not putting the pins properly. I was also getting the same issue and finally found that the pins of the LM1117 is different than what symbolically mentioned over internet.

From left to Right =>

  • first pin is Ground
  • Second Pin is VOUT
  • Third Pin is VIN

enter image description here

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