/HC-SR04

Verilog interface for HC-SR04 Ultrasonic Ranging Module

Primary LanguageVerilogOtherNOASSERTION

HC-SR04

Contents of Readme

  1. About
  2. Modules
  3. IOs of Modules
  4. Calculation of Distance
  5. Test
  6. Status Information
  7. Issues
  8. Licence

Repo on GitLab Repo on GitHub

About

HC-SR04 is an ultrasonic distance sensor. It provides 2cm to 400cm of non-contact measurement functionality with a ranging accuracy that can reach up to 3mm.

HC-SR04 uses 5V logic!

Modules

Module hc_sr04 provides an interface for HC-SR04. It generates 10µs trigger signal, Trig, and counts the length of the echo signal, Echo. Length of the echo signal counted in number of cycles, multiples of 10ns.

Module refresher250ms generates a measure signal every 250ms when enabled.

IOs of Modules

Port Type Width Description
clk I 1 System Clock (100 MHz)
rst I 1 System Reset
measure I 1 Initiate a new measurement
state O 2 State of the module, for debug etc
ready O 1 Module is not busy
echo I 1 Echo pin of HC-SR04
trig O 1 Trigger pin of HC-SR04
distanceRAW O 22 Length of the echo signal, multiples of 10ns

I: Input O: Output

Calculation of Distance

distanceRAW should be divided with 100 to calculate time in µs.

  • distanceRAW / 100 = Time (µs)

Distance can be calculated using following formula:

  • Distance (cm) = Speed of sound (cm/µs) × Time (µs) / 2

Where Speed of sound (cm/µs) = 0.0346 at 25°C

Temperature of the environment can change the speed of sound. It can be calculated via:

  • Speed of sound (cm/µs) = (331.3 + 0.606 * Temp) / 1000

Where Temp is the environment temperature in °C.

Formula above assumes 0% humidity.

Source: Wikipedia

Test

HC-SR04 uses 5V logic!

HC-SR04 require an external 5V supply. TXS0104E voltage level shifter is used to convert echo and trig signals between 3.3V and 5V.

testboard.v is used to test interface. echo and trig are connected to JA header. Sixteen least significant bits of distanceRAW is connected to seven segment display, remaining bits are connected to least significant bits of leds. Most significant bit of the leds connected to ready. Down button can be used to get a single measurement. SW15 can be used to enable refresher250ms module.

Status Information

Last Test: 16 January 2021, on Digilent Basys 3.

Issues

  • Keeping measure high breaks the module.

Licence

CERN Open Hardware Licence Version 2 - Weakly Reciprocal