Question on level shifting

Hi:

I posted an earlier question on digital pins in which I was informed that I was erroneously using a level shifter to accomplish a drop in voltage from the 5v digital output pins on an Arduino Uno to 3v to drive 3v LED's. Instead I should have used current limiting resistors for that purpose.

So, I am now wondering what is the proper use of level shifters? When can/should they be used instead of adding resistance to accomplish voltage drops?

In particular, one aspect of the motion sensing system I was trying to create relies on those inexpensive 433MHz RF chips all over EBay to perform the communication between the motion sensor and the base unit. I deployed one of the motion sensors, which I confirmed was functional in close proximity to the base unit, outside and I do not get a signal on the base unit when motion occurs in front of the sensor.

In the sensor unit, I am using a 9v battery to power a Arduino Nano via the Vin pin and using two 5v pins of the Nano to power both the sensor and the RF chip. In Google searches I found that if I were to increase the voltage on the RF chip (it can handle up to 12v) I would get greater range. So, could a level shifter be used to enable me to power the RF chip directly from the 9v or 12v source but trigger communications from a 5v digital pin on the Nano or should I use a transistor to convert the 5v signal to a 9v/12v one for transmission?

Thanks!

https://learn.sparkfun.com/tutorials/using-the-logic-level-converter

I do not know who advised against the convertors, but series resistance or resistor voltage dividers are only appropriate in a few cases. Resistor logic level converter cause more problems than they solve - IMO.

Ray

You have quoted the example of LED where the supply exceeds the power requirements of the LED and, therefore, a voltage drop by means of a resistance is required. This is effectively a one way change from a high to a low voltage.

The level shifter is normally a 2 way device for matching signal voltages. You are interfacing 2 devices together, one which uses voltage x as its signal voltage and one which uses voltage y as its signal voltage. Example: You want to connect a 5v I2C LCD display to the I2C bus of a 3.3v ESP8266. Since the ESP8266 does not tolerate 5v on its pins, you require a level shifter to interface the two devices without damaging the lower voltage (ESP8266) device. In this case there are 4 connections to the level shifter (excluding common ground): The native supply voltage of device 1 , the LCD. The native supply voltage of device 2 , the ESP8266. The signal connection(s) of device 1 the LCD. The signal signal connection(s) of device 2 ESP8266.

If you go back to your example of the LED. Imagine that the power requirements of LED were not reached (say voltage too low ), no amount of series resistors would solve that. You would then require an additional power supply to the LED which matched its [the LED's] power requirements, but would then have to ensure that this was compatible with the device controlling the LED. It is still a one way change, but in the other direction. In this case from Low to High.

So, could a level shifter be used to enable me to power the RF chip directly from the 9v or 12v source but trigger communications from a 5v digital pin on the Nano

On the low end OOK/ASK 433 MHz modules I have used, you can power them with anywhere from 5-12 volts, and the transmission power will go up with the voltage. The RX/TX connection going to the Arduino work fine at the 5V logic level and no level shifting is required.

Just to make sure I understand your reply, I can just wire the gnd and the VCC of the 433MHz RF chip to the 9v battery and connect the signal pin to the 5v digital pin on the Arduino to generate the signal and the RF Chip will take and broadcast the signal at 9v? Is that correct?

Thanks!

Just to make sure I understand your reply, I can just wire the gnd and the VCC of the 433MHz RF chip to the 9v battery and connect the signal pin to the 5v digital pin on the Arduino to generate the signal and the RF Chip will take and broadcast the signal at 9v? Is that correct?

Yes, for the TX module. The RX module runs at 5v.