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So I purchased the JDY-10 BLE 4.0 module and a very small MCU which only is capable of feeding 5v.

Since I'm not an electrical engineer, I've been reading a bit on the internet, and so far, I understand that the Bluetooth module will be fried if I hook it up to a 5v power source. As far I can understand, a voltage divider is not usually the way to go, but would it be okay in this case? - I plan to put this on a PCB that I make on my own, therefore the solution should be fairly lightweight/simple.

Furthermore, would the RX pin require a pulldown resistor? (The datasheet doesn't reveal anything in that regard - and to be honest, I don't think it has one)

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    \$\begingroup\$ A voltage divider is okay for signals, but not for power. If you need to power it with 3V3, just get a small linear regulator. \$\endgroup\$ – Hearth Nov 25 '18 at 21:01
  • \$\begingroup\$ A voltage divider will lead to using more power than you actually need, resulting in shorter battery life. \$\endgroup\$ – RubberDuck Nov 25 '18 at 21:04
  • \$\begingroup\$ Thank you for your answer. :-) Does that mean that the TX pin from the MCU should have a voltage divider? Do you recommend any through-hole linear regulators for this purpose? \$\endgroup\$ – Jeppe Christensen Nov 25 '18 at 21:05
  • \$\begingroup\$ @JeppeChristensen If you're making a custom PCB for it I recommend not using through-hole parts. A SOT-23 linear regulator and one or two MLCC caps will do everything you need in the space of a few square millimeters. I don't know how easy it is to find through-hole parts rated to work at such low power levels, either. If you must use through-hole parts, though, the LM2936 series has a 3.3V model, so maybe use that? It's about ten times the price of an equivalent surface-mount part though. \$\endgroup\$ – Hearth Nov 25 '18 at 21:19
  • \$\begingroup\$ Thank you for your answer @Felthry. Price is not a big issue as is, but I don't have the option to mount SMD components unfortunately :-( - I'm unfamiliar with the LM2936 series you are mentioning, but i did find this: sparkfun.com/products/526 Do you think it will do the job? \$\endgroup\$ – Jeppe Christensen Nov 25 '18 at 21:24
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A voltage divider is okay to use for signals, but not for power as it either gives you a very high supply resistance or wastes a lot of power. It's better to use a voltage regulator instead.

Since your device doesn't need too much current (though it doesn't have a datasheet, which is a big red flag in my book), the TC1014-3.3 would probably be my choice. It's cheap, in a SOT-23-5 package that's a good compromise between small and easy-to-solder, and it has a nice low quiescent current.

If you absolutely must use a through-hole part, (which I repeat that I do not recommend), an LP2950-3.3 or the massively-overkill LM1117T-3.3 should suit your needs.

For any of these, don't forget that they'll need an output capacitor. I'd just go with cheap ceramic ones, but you can use electrolytics if they need high capacitance and you can find one that has a suitably low ESR. I didn't bother checking the datasheets of the ones I recommended, but almost all linear regulators recommend at least one input capacitor and one output capacitor, and most require the output capacitor. These are usually around the 1μF range, so nothing too extreme.

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  • \$\begingroup\$ Again, thank you :-) Do you reckon that I need a pull-down resistor and voltage divider for the RX pin - now that the module is 3v3 compatible? \$\endgroup\$ – Jeppe Christensen Nov 25 '18 at 21:50
  • \$\begingroup\$ @JeppeChristensen I couldn't tell you about pull-down resistors but you'll definitely want a voltage divider. Read your datasheets to see what sort of pullup/pulldown you'll need. \$\endgroup\$ – Hearth Nov 25 '18 at 21:54
  • \$\begingroup\$ @JeppeChristensen And please don't mark this as the accepted answer yet! It's recommended that you wait at least a day for other answers to come in, which may be better than mine--but if people see the question already has an accepted answer they're less likely to write their own, possibly better ones. \$\endgroup\$ – Hearth Nov 25 '18 at 21:55
  • \$\begingroup\$ Understood, i will mark it accepted in a couple of hours then. \$\endgroup\$ – Jeppe Christensen Nov 25 '18 at 21:56
  • \$\begingroup\$ The microamp rating is most likely when it's sleeping. Typical BLE devices run at around 15-20mA when receiving and transmitting, depending on transmit power output levels (further down it states the active part is a TI cc2541). Since this is 4 orders of magnitude difference you would need some kind of active regulation for power. For -input- signals, resistive dividers should work but watch out for RC rise times vs pin current drive capabilities. Going from the 3.3V level to a 5.0 level can be tricky if the 5V part input(s) are not TTL level compatible. \$\endgroup\$ – isdi Nov 26 '18 at 0:51

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