Pro Mini NRF24l01+ and button setup

Projects General Guidance
1

Hello all,

I'm looking for a little bit of assistance with a project I'm doing. I'm new to Arduino, and I've looked for answers via Google, but couldn't find anything.

Anyhow, I have the following assembled on a breadboard:

(Attached to the post)

I was about to plug the power in, but I wasn't confident that I wouldn't damage something, so I decided to check here.

So, I am wondering whether the above will work properly. The wireless chip is the NRF24l01+, and the board is a 5V 16MHz Arduino Pro Mini. The resistors are 220 Ohm (in the voltage divider).

The button code is:

void setup() { 
 pinMode(5, INPUT); 
}
void loop() {
 if(digitalRead(5)){
 	//send message
 }
}

If I understand correctly, the output from VCC is 5V (on a 5V Pro Mini) and that the Pro Mini I/O pins are 5V tolerant. I wasn't able to determine what the current is - would it be too much for the I/O ports?

Thank you very much for any assistance.

pro_mini_setup_sm.png
pro_mini_setup_sm.png1009×731 97.8 KB

2

Modify your post, click Additional Options, Browse to your locally stored picture, and Attach it.
Make sure its Not some 3000+ pixel wide behemoth - scale it down to like 1024 wide.

nRF24L01+
Single Chip 2.4GHz Transceiver
Product Specification v1.0

The NRF24l01+ has 5V tolerant IO:
• 5V tolerant inputs

but Requires 3.3V power:
• 1.9 to 3.6V supply range
• On chip voltage regulator
Absolute maximum ratings:
Note: Exceeding one or more of the limiting values may cause permanent damage to nRF24L01+.
VDD Supply voltage if input signals >3.6V: 3.3V Max

Supply current needed:
• 11.3mA TX at 0dBm output power
• 13.5mA RX at 2Mbps air data rate
• 900nA in power down
• 26?A in standby-I

How are you supplying that?

3

CrossRoads:
nRF24L01+
Single Chip 2.4GHz Transceiver
Product Specification v1.0

The NRF24l01+ has 5V tolerant IO:
• 5V tolerant inputs

but Requires 3.3V power:
• 1.9 to 3.6V supply range
• On chip voltage regulator
Absolute maximum ratings:
Note: Exceeding one or more of the limiting values may cause permanent damage to nRF24L01+.
VDD Supply voltage if input signals >3.6V: 3.3V Max

Supply current needed:
• 11.3mA TX at 0dBm output power
• 13.5mA RX at 2Mbps air data rate
• 900nA in power down
• 26?A in standby-I

How are you supplying that?

Thank you for your response. I've modified my post as requested.

Well, there's 5 volts coming from the Pro Mini, which goes through the voltage divider to make it 3.3 volts. I think that takes care of the power supply for the RF chip (please correct me if I'm wrong).

For the current, I'm not sure exactly (the multimeter I'm using isn't able to measure it, it seems). If I understand correctly, the pins on the Pro Mini have a draw limit of 40mA (but according to what I've read, a typical 9V battery has about 30mA of current). My assumption is that the pins on the Pro Mini are 40mA tolerant, too.

Have I gone wrong somewhere?

(I haven't powered it up yet, since I want to make sure I haven't made a mistake.)

Thanks again.

4

AKG4:
Well, there's 5 volts coming from the Pro Mini, which goes through the voltage divider to make it 3.3 volts. I think that takes care of the power supply for the RF chip (please correct me if I'm wrong).

Hi akg4, sorry but you are wrong. A voltage divider will only give a consistent output voltage as long as you draw no (or nearly no) current.

The ideal answer is a 3.3V regulator. If you don't have one, use 2 or 3 diodes to drop around 1.5V off the 5V supply and feed that to the nrf. The voltage drop accross a diode doesn't change too much with current, unlike a resistor. If you have no diodes a red led might do for now! They drop about 1.8~2V.

Paul

5

Exactly. You will have
5/660ohm = 7.6mA without the radio and 1.67V across the top resistor.
Now add the added currents for the radio, and your voltage is all over the place:
one voltage at 11.3mA, (18.9ma x 220 ohm = 4.16V)
a 2nd at 13.5mA, (4.642V)
a 3rd at 900nA, (1.87V)
and a 4th 26?A. (1.67, the only one that is close)

You need a regulator.

6

If you have an Uno or a Nano, those have 3.3V outputs.

To get any decent range out of the nrf modules, you need a big cap (at least 10uF) across the 3.3v and Gnd connections to allow for the sudden current peaks demanded during transmissions.

7

Thanks for the replies.

I have a Nano, so I'll use that to test the setup instead.

It seems that I'll have to order some voltage regulators for the Pro Minis - is there a particular kind that you would recommend for my situation?

I went to look on Digikey, and found a few that I think would work:

Thanks again for your help.

8

Any LDO, 100ma regulator should be capable.
500mA is overkill, there is only 150mA of 5V current to start with.

9

CrossRoads:
Any LDO, 100ma regulator should be capable.
500mA is overkill, there is only 150mA of 5V current to start with.

Ah, okay. So anything over 150mA would work, then?

Thanks again.

10

Yes.

11

You only need to supply 15-20mA. On boards without a 3v3 regulator I just power the nRF from 5V with a couple of diodes to drop the voltage, and they work fine.