News How to Use an Ultrasonic Sensor with Raspberry Pi Pico

[Admin]

Use an ultrasonic sensor to take distance measurements with your Raspberry Pi Pico.

How to Use an Ultrasonic Sensor with Raspberry Pi Pico : Read more

 

[Sel199]

I was having an issue which I thought was the code but it seems to be a wiring issue, the connections seem to be intermitent so it only work when I fiddle with the wires.
Odd though as I've changed all the wires out and even swapped boards and it still won't run.

Update it turns out I had the 5v version Sensor HC-SR04 however I also had a US-015 sensor also 5v wich works perfectly.

 

[kopjasa]

You can use the 5V version e.g.: HY-SRF05. Just you need the change the 3V3 pint to the VBUS pin and you have to feed through USB port. (Please note that in this case you have to use a voltage divider for the ECHO wire.)

 

[dathai]

You can save 3 wires if you line up the Trigger with pin 16 and echo with 17, that puts GND with GND .
One wire is needed to go from a 3V3 or the VSYS/VBUS if you need 5V and are powering via micro-USB.

 

[ZukaBlue]

I'm curious how some of this works in terms of the code.

I keep looking at this section:

while echo.value() == 0:
signaloff = utime.ticks_us()
while echo.value() == 1:
signalon = utime.ticks_us()
timepassed = signalon - signaloff
dist = (timepassed * 0.0343) / 2

I keep trying to figure out exactly how this works. To my brain, it seems like this is just measuring the length of the incoming pulse. Someone correct me if I'm wrong, or let me know how this all works, but this is my logic -

1. Send out a pulse
2. While we are not detecting a received pulse, keep updating a number. Ex:
   1. 1001, 1002, 1003, 1004, 1005
3. While we are receiving a pulse, update a different number. Ex:
   1. 1006, 1007, 1008
4. Subtract the first from the second:
   1. 1008 - 1005 = 3
5. This just measures the number of microseconds that we actually detect the pulse returning and not the time that it took for the pulse to bounce back.

How am I thinking of this wrong? Am I misunderstanding what utime.ticks_us() does? Is that simply counting up from the time it is called and then starting to count again when it starts detecting a high signal? My thought would be to take just a single measurement of utime.ticks_us() immediately after sending a high pulse from the trigger. That would find some value of microseconds and store it as a value, then we wait until we get a high pulse and do nothing until then. When we do get a high pulse we mark the beginning of that high pulse in terms of microseconds, and then we can find the difference between the initial out pulse and the return pulse, multiply by the speed of sound in cm/s, and then divide by 2.


Edit: Obviously I know that it does work, I'm just trying to piece together exactly how it works. Also, the signaloff and signalon are defined in the while loops, but then they are used later on again outside of those indents. Why does it allow this?

 

[Jpico]

You can save 3 wires if you line up the Trigger with pin 16 and echo with 17, that puts GND with GND .
One wire is needed to go from a 3V3 or the VSYS/VBUS if you need 5V and are powering via micro-USB.

You're so right on this!

you saved us from the spaghetti cables!

 

[PicoCrook]

I'm curious how some of this works in terms of the code.

I keep looking at this section:

while echo.value() == 0:
signaloff = utime.ticks_us()
while echo.value() == 1:
signalon = utime.ticks_us()
timepassed = signalon - signaloff
dist = (timepassed * 0.0343) / 2

I keep trying to figure out exactly how this works. To my brain, it seems like this is just measuring the length of the incoming pulse. Someone correct me if I'm wrong, or let me know how this all works, but this is my logic -

1. Send out a pulse
2. While we are not detecting a received pulse, keep updating a number. Ex:
   1. 1001, 1002, 1003, 1004, 1005
3. While we are receiving a pulse, update a different number. Ex:
   1. 1006, 1007, 1008
4. Subtract the first from the second:
   1. 1008 - 1005 = 3
5. This just measures the number of microseconds that we actually detect the pulse returning and not the time that it took for the pulse to bounce back.

How am I thinking of this wrong? Am I misunderstanding what utime.ticks_us() does? Is that simply counting up from the time it is called and then starting to count again when it starts detecting a high signal? My thought would be to take just a single measurement of utime.ticks_us() immediately after sending a high pulse from the trigger. That would find some value of microseconds and store it as a value, then we wait until we get a high pulse and do nothing until then. When we do get a high pulse we mark the beginning of that high pulse in terms of microseconds, and then we can find the difference between the initial out pulse and the return pulse, multiply by the speed of sound in cm/s, and then divide by 2.


Edit: Obviously I know that it does work, I'm just trying to piece together exactly how it works. Also, the signaloff and signalon are defined in the while loops, but then they are used later on again outside of those indents. Why does it allow this?

I'm in the same boat. This is the code that I would write:


signaloff = utime.ticks_us() # to get the time from when the pulse ended
while echo.value() == 0:
pass # wait for a signal.....
signalon = utime.ticks_us() # get new time
timepassed = signalon - signaloff # this is now the time from when the pulse stopped being sent to when it's first detected - the return trip for the sound


I don't get the listed code either.