I am trying to utilise a Raspberry Pi's 5V output to push more current towards sensors connected to an MCP23017 i2c port expander. However, the MCP23017 requires that I down-convert the voltage to 3.3V.

To do convert from the Raspberry Pi's 5V supply to 3.3V, I'm using an LD1117V33 voltage regulator, a 100nF 16V ceramic capacitor, and a 10uF 16V electrolytic capacitor connected as shown in the diagram below.

5V to 3.3V conversion diagram

  • Pi's 5V output goes into the left pin of the LD1117V33, which connects to the the + (left) pin of the electrolytic capacitor.
  • The middle pin of the LD1117v33 connects to the - (right) pin of the electrolytic capacitor, the left pin of the ceramic capacitor, and through to the ground.
  • The right pin of the LD1117V33 connects to the right pin of the ceramic capacitor. It is supposed to output a 3.3V supply for the MCP23017 (but it does not).
  • MCP23017 output connects to the ground.
  • The ground in this diagram connects to the Pi's ground.

The MCP23017 works normally when connected to the Pi's 3.3V output. Why doesn't it work with the power regulator, shown above, connected to the Pi's 5V output?

  • \$\begingroup\$ Do you have a multimeter? You should measure voltages. Also, just be sure to double-check the pins against the datasheet. \$\endgroup\$
    – Jashaszun
    Commented Jun 16, 2017 at 21:39
  • \$\begingroup\$ voltages, eh. i should do that. yeah, datasheet pins is proabbly it, i tried different pins and it got really hot so i got worried. thanks, mate. \$\endgroup\$ Commented Jun 16, 2017 at 21:50
  • 1
    \$\begingroup\$ Why are you hooking it up without checking the datasheet? That's a pretty surefire way to ruin components. \$\endgroup\$
    – Jashaszun
    Commented Jun 16, 2017 at 22:11
  • \$\begingroup\$ thanks. im follwoing a step by step tutorial without having full knowledge of what im doing. \$\endgroup\$ Commented Jun 17, 2017 at 14:53

2 Answers 2


If you look at the datasheet, you have the pins wrong. enter image description here

Pin 1 should be Ground, Pin 2 should go to your sensors, pin 3 should go to the 5V from the Raspbery Pi.

  • \$\begingroup\$ so its probably hte pins, same as the other comment. oops, probably should have checked datasheet. thank you. \$\endgroup\$ Commented Jun 16, 2017 at 21:52
  • 2
    \$\begingroup\$ NEVER use a part you haven't used before without checking the datasheet. \$\endgroup\$
    – Nino
    Commented Jun 16, 2017 at 22:04

ok, so initially i was too scared to try to troubleshoot because i was wroking on a tutorial andi was worried i was going to fry my pi, but i checked the datasheet and wired it up accordingly and checked the voltages wtihy m multimetre and im getting 3.5v which is pretty close, so thanks everyone.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.