dparson55
commented
7 months ago I was not able to recreate the issue, maybe you are not transmitting on channel 0 when calling scanChannel. You might be confusing channel and radio id.
channel controls the frequency that the radio uses when transmitting and receiving data. When channel = 0 the radio uses a frequency of 2400MHz, when channel = 1 the radio uses 2401MHz. As detailed in NRFLite.h, any channel between 0 and 125 can be used, so any frequency between 2400 and 2525MHz.
radio_id controls the address used for data packets and can be any number between 0 and 255. The address is one of the fields inside a data packet and allows radios that are listening on the same channel to identify packets that are meant for receiption. If a radio receives a data packet, it looks at the address inside the packet and if it does not match the address assigned to the radio, the packet is ignored.
This code scans channel 0 (2400MHz) to see how noisy it is:
#include "SPI.h"
#include "NRFLite.h"
const static uint8_t RADIO_ID = 0;
const static uint8_t PIN_RADIO_CE = 9;
const static uint8_t PIN_RADIO_CSN = 10;
NRFLite _radio;
void setup()
{
Serial.begin(115200);
// Setup the radio. It will default to channel 100 but this will be changed by scanChannel in the loop.
_radio.init(RADIO_ID, PIN_RADIO_CE, PIN_RADIO_CSN);
}
void loop()
{
// Scan channel 0 for noise and print out the results.
Serial.println(_radio.scanChannel(0));
}Initially scanChannel reports 0-2 as shown in the serial monitor and serial plotter, which is not very noisy.
This code creates a lot of noise on channel 0 (2400MHz):
#include "SPI.h"
#include "NRFLite.h"
const static uint8_t RADIO_ID = 1;
const static uint8_t PIN_RADIO_CE = 9;
const static uint8_t PIN_RADIO_CSN = 10;
NRFLite _radio;
void setup()
{
// Setup the radio to use channel 0.
_radio.init(RADIO_ID, PIN_RADIO_CE, PIN_RADIO_CSN, NRFLite::BITRATE2MBPS, 0);
}
void loop()
{
// Send the number 77, which is 1 byte in length. The data packet will be addressed to radio id 99.
// It is not necessary for radio 99 to exist since the purpose of this code is to flood channel 0 with signals.
_radio.send(99, 77, 1);
}When the above code is run, scanChannel returns a value between 23 and 33. I have the radios about 0.5m from each other and they are in line of sight.
As mentioned in the Basic_TX example, NRFLite assigns the radios to use channel 100 by default (2500MHz), so you need to change it to 0 if that is the channel you would like to use. You can use the ChannelScanner example to find the channel that has the least amount of noise in your environment and below is a subset of mine for an example (channels 14-38 are really noisy so I would not want to use them for projects).
10:21:32.568 -> Use a channel without existing signals.
10:21:32.568 -> Each X indicates a signal was received.
10:21:32.568 ->
10:21:32.670 -> Channel 0 X
10:21:32.773 -> Channel 1 X
10:21:32.887 -> Channel 2
10:21:33.017 -> Channel 3 X
10:21:33.102 -> Channel 4 X
10:21:33.231 -> Channel 5 XX
10:21:33.350 -> Channel 6 X
10:21:33.422 -> Channel 7 X
10:21:33.551 -> Channel 8 X
10:21:33.685 -> Channel 9
10:21:33.801 -> Channel 10
10:21:33.870 -> Channel 11
10:21:33.999 -> Channel 12
10:21:34.123 -> Channel 13 XXX
10:21:34.253 -> Channel 14 XXXXXXXXXXXXXXX
10:21:34.340 -> Channel 15 XXXXXXXXXXXXXX
10:21:34.471 -> Channel 16 XXXXXXXXXXXXXXXXXXXXXX
10:21:34.588 -> Channel 17 XXXXXXXXXXXXXX
10:21:34.674 -> Channel 18 XXXXXXXXXXXXXXXX
10:21:34.804 -> Channel 19 XXXXXXXXXXXXXXXXXXXXX
10:21:34.922 -> Channel 20 XXXXXXXXXXXXXX
10:21:35.006 -> Channel 21 XXXXXXXXXXXXXXXX
10:21:35.124 -> Channel 22 XXXXXXXXXXXXXXX
10:21:35.254 -> Channel 23 XXXXXXXXXXXXXXX
10:21:35.343 -> Channel 24 XXXXXXXXXXXXXXX
10:21:35.459 -> Channel 25 XXXXXXXXXXXXXXXXXXXXX
10:21:35.574 -> Channel 26 XXXXXXXXXXXXXXXXXXXXXXXXXXX
10:21:35.695 -> Channel 27 XXXXXXXXXXXXXXXXXXXXXX
10:21:35.809 -> Channel 28 XXXXXXXXXXXXXXXXXXXXXXX
10:21:35.922 -> Channel 29 XXXXXXXXXXXXXXXXXXXXXXXXXXXX
10:21:36.042 -> Channel 30 XXXXXXXXXXXXXXXXXXXX
10:21:36.110 -> Channel 31 XXXXXX
10:21:36.229 -> Channel 32 XXXXXX
10:21:36.374 -> Channel 33 XXXXXXXXXXXXXXXXXXXXXXXXX
10:21:36.462 -> Channel 34 XXXXXXXXXXXXXXXXXXXXXXXX
10:21:36.574 -> Channel 35 XXXXX
10:21:36.696 -> Channel 36 XXXXX
10:21:36.812 -> Channel 37 XXXXXX
10:21:36.928 -> Channel 38 XXXXXXXXXXX
10:21:37.041 -> Channel 39
10:21:37.160 -> Channel 40 XJust to be clear, scanChannel does not return the RSSI because the nRF24L01 chip does not have the ability to measure that, the nRF24L01 chip can only report a 1 if it sees a signal on a channel and 0 if it does not. The datasheet indicates that it will be able to detect a signal if the strength is stronger than -64 dBm for 170 microseconds. Using this information, as detailed in NRFLite.h, scanChannel asks the radio if it sees a signal on a channel a given number of times and by default, it takes 255 measurements. If it sees a signal 10 times, a 10 is returned, if it does not see any signals, a 0 is returned. You can see internally what NRFLite is doing here, it assigns the nRF24L01 to the specified channel, puts it into RX mode and waits 400 microseconds for a signal to be detected, turns off RX mode and increments a counter if a signal was detected, then repeats the process up to the specified measurementCount. So if scanChannel returns a 0 it means it checked 255 times, waiting 400 microseconds for a signal each time, and over all those checks the nRF24L01 never detected a signal.
gordon4liu
Hi , My Antenna distance is 15cm between the tx module and rx module. I can receive meaasge form the tx module (channel=0) but the signal strength is always 0 (<-64dBm). Does it HW or SS issue??
==== Rx module == while (_radio.hasData()) {
uint8_t signalStrength = _radio.scanChannel(0); Serial.println(" RSSI= " + String(signalStrength));