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I'm working with a uC and a Bluetooth Module. I need the lowest current consumption in this project because it is intended to be a mobile device. Thus, I'm using sleep modes on the uC. Now, I've encountered a problem:

The Bluetooth module has to receive a High level (3.3V) on an input pin when the uC is in sleep mode (to let it know that communication can't be done right now). Problem is when uC is going full sleep mode (as I want) all pins go low (0V). Therefore, I think I should use a voltage inverter.

I have researched and found two possible options:

  1. to use a common transistor as a switch inverter. (base connected to a resistor and uC pin, collector to a resistor and Bluetooth Module input pin, and emisor to ground)

  2. to use a logic gate inverter as 74HC1G04.

I got a few questions:

  • Is it really that simple to use a logic gate inverter? What is the down side? why do people use transistors?
  • Which option would get the lowest current consumption?
  • I have seen some transistor switching guides. They talk about the load current needed to turn on a motor, bulb or whatever they want to have at the end of the transistor switch. But in my case, I have a input pin of a low energy bluetooth module which I believe does not need a big current load... So, any comment on how to know what current is needed for this to work?

Btw, I am a noob in Electronics Engineering and I am ready to learn!

I'm using a Atmega328 as uC and a RN4020 as BLE (bluetooth low energy). Thanks for your help!

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  • \$\begingroup\$ Read the data sheet for the BLE device and seee what it says. If it's less than 1mA then virtually all logic gates that work at the voltage levels used will be good enough. \$\endgroup\$ – Andy aka Nov 24 '15 at 18:57
  • \$\begingroup\$ Also check if the uC puts the I/O in tristate mode, then a simple pull-up resistor will do the job. \$\endgroup\$ – Ali Nov 24 '15 at 19:01
  • \$\begingroup\$ If you use a transistor then a mosfet would take less power than a BJT because there is no DC base current .Also your parts count is lower due to no base resistor.If you dont need high speed the pullup resistor can be a high value giving low power drain.For high speed the gate will do better. \$\endgroup\$ – Autistic Nov 24 '15 at 20:08

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