New board, 5v Vs 3.3v, nrf24l01

I have been working on this board. While adding a header for nrf24l01, I got few doubts:

1, what is the pro and con of using 5v instead of 3.3V; Because the nrf24l01 uses 3.3v, and I don’t want to have 2 regulator on board. Maybe I will run everything with 3.3v.

2, I am using pin 0 for CSN and Pin 1 CE for the nrf24l01, will that work? and also what is IRQ connected to? N/C?

3, I use 3 buttons on one pin. Is my connection correct?

Hi,

  1. The Atmega328 probably won’t run reliably at 16MHz with only 3.3V, you need 5V for that. But you seem to be using the internal oscillator, so it will be 1MHz or 8MHz anyway.

  2. What do you mean by Pin 0? Arduino digital pin 0? INT will need to be connected to a digital pin also, for the NRF libraries to work, I seem to remember.

  3. Yes, that should work. Not sure about that led on the SCK line. What it it for?

What values are you using for R1 - R8? If these are not high enough, you will overload pins 23-26 (whichever those are). Remember max current from any pin should be 40mA, but lower would be better for reliability. You may need to put 4 transistors in there.

Paul

eaa578cfffe047203f8c3ec8ef8cb39e3305cd71.png

PaulRB:
Hi,

  1. The Atmega328 probably won’t run reliably at 16MHz with only 3.3V, you need 5V for that. But you seem to be using the internal oscillator, so it will be 1MHz or 8MHz anyway.

  2. What do you mean by Pin 0? Arduino digital pin 0? INT will need to be connected to a digital pin also, for the NRF libraries to work, I seem to remember.

  3. Yes, that should work. Not sure about that led on the SCK line. What it it for?

What values are you using for R1 - R8? If these are not high enough, you will overload pins 23-26 (whichever those are). Remember max current from any pin should be 40mA, but lower would be better for reliability. You may need to put 4 transistors in there.

Paul

eaa578cfffe047203f8c3ec8ef8cb39e3305cd71.png

1, yes, it’s running at 8mhz ( will there be problems uisng nrf24l01 @ 8mhz?)

2, yes, pin0 means digital pin0

3, sck is pin 13. most boards have a led on pin13.

4, R1-R8 are 1k. don’t worry about that.

For convenience IRQ should go to PD2 or PD3.

I have seen projects using nrf2401 with 8MHz 3.3V Pro Mini, so it must be ok.

Have you tested your led display? With those 1K series resistors, you will only get around 1.5mA per segment. Combine that with a 1 in 4 multiplex and the average current will only be around 0.3mA, which might be very dim.

PaulRB:
I have seen projects using nrf2401 with 8MHz 3.3V Pro Mini, so it must be ok.

Have you tested your led display? With those 1K series resistors, you will only get around 1.5mA per segment. Combine that with a 1 in 4 multiplex and the average current will only be around 0.3mA, which might be very dim.

Yes. It has been tested. guess a pro like yourself can be wrong sometimes too.

Here is a photo of the led display.

arduinomagbit: guess a pro like yourself can be wrong sometimes too.

If I was a pro, i would be wrong sometimes, I'm sure. But I'm just an enthusiast, like yourself, who needs help from other pairs of eyes to spot mistakes as early as possible.

Those led segments must be very efficient to be so readable at 0.3mA!

PaulRB: If I was a pro, i would be wrong sometimes, I'm sure. But I'm just an enthusiast, like yourself, who needs help from other pairs of eyes to spot mistakes as early as possible.

Those led segments must be very efficient to be so readable at 0.3mA!

dear paul 5-2=3v/1000=0.003 which is 3ma?

I have an Atmega 328 running on the internal 8MHz oscillator and connected to an nRF24 with the whole thing powered off 2 x AA batteries.

On another board I have just one LM317 voltage regulator powering both at 3v (or maybe a little more).

...R

arduinomagbit: dear paul 5-2=3v/1000=0.003 which is 3ma?

But you want to run on 3.3V, so it would be (3.3-2)/1K=1.3mA. Then with 1 in 4 multiplexing, the average would be 1.3/4=0.325mA.

You could try 330R resistors, giving max current for the digit common pins of around 31mA which should be ok. This would give an average segment current of 1mA.

Robin2: I have an Atmega 328 running on the internal 8MHz oscillator and connected to an nRF24 with the whole thing powered off 2 x AA batteries.

On another board I have just one LM317 voltage regulator powering both at 3v (or maybe a little more).

...R

Okay. thanks for the confirmation. here is the final circuit and finished board design.

|500x219

|500x207

PaulRB: But you want to run on 3.3V, so it would be (3.3-2)/1K=1.3mA. Then with 1 in 4 multiplexing, the average would be 1.3/4=0.325mA.

You could try 330R resistors, giving max current for the digit common pins of around 31mA which should be ok. This would give an average segment current of 1mA.

okay. sounds good to me. i will try it out.