installing RF-24G in a 5V circuit

Wireless & IoT
1

Hello Friends,

Just wondering if there is an easy way to use the RF-24G in a circuit that uses 5V. I am well aware that these units require 3.3V max. I don’t want to burn out the module.

I am not using a MAX232 in my circuit, just hooking up the module to an avr directly. The power for the avr cannot be changed (well not easily).

Can anyone point me to a schematic somewhere? I have searched but didn’t find much.

2

AFAIK, the nrf2401 that is used on the RF-24G does not have 5V-tolerant inputs. I also don’t think the RF-24G has an onboard regulator, which means you can’t power it using 5V.

My suggestion is to go with the nrf24L01 chips, which are on Sparkfun’s MiRF-v2 boards. You can power them with 5V, since the boards have an on-board regulator. Also, the 24L01’s inputs are 5V tolerant, and its output are enough to switch a 5V microcontroller’s input pin on and off properly. Also, I have several tutorials for using this chip with PIC’s and ARM7 chips at my website, so you could simply translate them for your chip if you’re using C.

Now if you’ve already gotten the RF-24G and can’t go for the MiRF-v2, you’ll have to get a regulator to power the RF-24G at 3.3V, and you will also have to do some voltage translation on the lines that go from your AVR to the RF-24G to take them from 5V to 3.3V. There have been quite a few threads discussing different ways to translate I/O voltage on this forum, so a quick search should turn something up.

3

brennen:
you will also have to do some voltage translation on the lines that go from your AVR to the RF-24G to take them from 5V to 3.3V. There have been quite a few threads discussing different ways to translate I/O voltage on this forum, so a quick search should turn something up.

Thanks for your reply.

I already purchased the 3V modules, so I guess I will have to find a solution.

Regulating the power for the module isn’t the problem, its the I/O lines as you mentioned above. I will search the forum.

Thanks

4

In a similar case to yours, we used 2 diodes in series to drop Power supply from 5 to 3.6 circa, and simple resistors from 5V PIC to RF24 inputs, and nothing the other way around. It did work pretty fine.

5

I saw another post (here or on avrfreaks) regarding the use of a 74HC4050. I purchased some and haven’t had time to try it yet.

6

brennen:
My suggestion is to go with the nrf24L01 chips, which are on Sparkfun’s MiRF-v2 boards. You can power them with 5V, since the boards have an on-board regulator. Also, the 24L01’s inputs are 5V tolerant, and its output are enough to switch a 5V microcontroller’s input pin on and off properly.

Still talking about the MiRF v2/nRF24L01, what about the MISO line, if there are other SPI devices that have a 5V MISO line on the same bus? Are any precautions needed?
7

OT:
Still talking about the MiRF v2/nRF24L01, what about the MISO line, if there are other SPI devices that have a 5V MISO line on the same bus? Are any precautions needed?

The 24L01 has 5V tolerant I/O, so you don't really have to worry about other 5V SPI devices on your bus.