A111: Sensor 1 does not communicate properly, is it connected?

Sensors Distance
1

Hello,

I have used the A111 sensor with the female header connected directly to a Pi 4’s male header without issue thus far. All Sparkfun examples work and return readings. However, when I try to extend the sensor away from the Pi using jumper wires, I get the error when trying to run the sparkfun_detector_distance_basic example “Sensor 1 does not communicate properly, is it connected?”. I have tried connecting only the pins specified in the [Hardware Assembly section of the A111 getting started guide, as well as connecting every single pin on the 26 pin header to the corresponding pin on the Pi with no luck (see pictures). I have verified continuity between every pin on the 26 pin header and their corresponding pin on the Pi. I have tried two separate A111 boards and they both have the same behavior. Can anyone help me?

N5hWbUD.jpg3456×4608 1.44 MB
https://i.imgur.com/N5hWbUD.jpg

qhuQlVv.jpg3456×4608 1.26 MB
https://i.imgur.com/qhuQlVv.jpg](Getting Started with the A111 Pulsed Radar Sensor - SparkFun Learn)

2

An additional picture, here is a scope plot of the SPI lines + EN and INT when it tries to communicate over the jumper wires. There is never a reply on the MISO line. You can also see CS (active-low) is indeed brought low before the CLK starts, and EN (active-high) is high the entire time. The only odd thing I see is the CLK seems to be missing every 9th pulse.

BW4O02S.jpg4608×3456 1.79 MB
https://i.imgur.com/BW4O02S.jpg

3

Hello ninjas28.

Unfortunately this board was designed to operate directly on top of a Pi and won’t work with an extension cable. I believe the A111 chip is very picky about how clean the signals it’s receiving from the Pi and lengthening the connection distance between the chip and Pi causes enough noise to cause problems.

The only thing I can think of that might help would be to build some sort of buffer board that sits under the shield to act as a signal conditioner, but this has not been tested.

4

Hi Chris,

Thanks for the response. After I saw your reply, I decided to wrap the jumper wires in aluminum foil and ground the shield and just see what happens. Lo and behold, as soon as I added enough aluminum foil it started working beautifully.

I will have to take noise considerations more seriously if I integrate this into a final design. Thanks for the assistance.

X91FOPi.jpg3456×4608 1.53 MB
https://i.imgur.com/X91FOPi.jpg

5

Thanks for trying that out and letting us know!