RF Pulse Distance Measurement System Using ESP8266 and RTL-SDR
This project aims to create a simple RF-based distance measurement system using an ESP8266 microcontroller to generate PWM pulses, an FM transmitter built with two 2N3904 transistors, and an RTL-SDR receiver to capture the transmitted signals. The system will measure the time taken for a signal to travel to a reflective surface and back, allowing for distance calculations based on the time-of-flight principle.
The FM transmitter circuit will use two 2N3904 transistors to create a simple oscillator and amplifier configuration.
Schematic Diagram:
+Vcc
|
R1
|
|-------|
| |
C1 C2
| |
--- ---
| | | |
--- ---
| |
---- ----
| | | |
| | | |
---- ----
T1 T2
(2N3904) (2N3904)
| |
Antenna |
GND
Component Values:
File > Preferences, and add this URL to "Additional Board Manager URLs":
http://arduino.esp8266.com/stable/package_esp8266com_index.json
Tools > Board > Board Manager, search for "ESP8266", and install it.Tools > Board.The following code generates PWM pulses on a specified pin connected to the base of the FM transmitter:
const int pwmPin = D1; // Pin connected to FM transmitter base
const int pulseDuration = 100; // Pulse duration in milliseconds
void setup() {
pinMode(pwmPin, OUTPUT);
}
void loop() {
// Send pulse
analogWrite(pwmPin, 255); // Full duty cycle
delay(pulseDuration);
analogWrite(pwmPin, 0); // Turn off pulse
delay(1000); // Wait before sending next pulse
}
When you send a pulse from the ESP8266, start a timer immediately.
Use SDR software to monitor when the pulse is received.
Use the formula:
import time
import numpy as np
from rtlsdr import RtlSdr
sdr = RtlSdr()
# Configure SDR parameters
sdr.sample_rate = 2.048e6 # Sample rate in Hz
sdr.center_freq = 100e6 # Set this to your transmitter frequency in Hz
sdr.gain = 'auto'
# Start receiving samples
print("Starting reception...")
start_time = time.time()
# Read samples and check for pulse (this is simplified)
samples = sdr.read_samples(256*1024)
# Process samples here (detect pulse)
# This could involve analyzing FFT or other methods
end_time = time.time()
# Calculate round-trip time in seconds
round_trip_time = end_time - start_time
# Calculate distance in meters
distance = (round_trip_time * 299792458) / 2
print(f"Distance measured: {distance} meters")
sdr.close()
Verify that your RF pulses are being transmitted correctly by monitoring them with SDR software.
Ensure accurate timing by comparing against known distances.
Use both RF distance measurements and any additional data from accelerometers if desired for enhanced accuracy.
This project outlines how to create an RF Pulse Distance Measurement System using an ESP8266, an FM transmitter built with two NPN transistors, and an RTL-SDR receiver. By following these steps, you can build a functional system capable of measuring distances based on time-of-flight principles using RF signals.
If you have any specific questions regarding components, wiring diagrams, or programming examples, feel free to ask!