Sharp GP2YOA21 IR sensor 5v issue

minnowahaw

Hey hi Giulio et alii,

For the construction of a series of sound installations I am trying to use the Sharp GP2YOA21 IR sensor to let the body of the spectator trigger the composition. The fabricator mentions in the data sheet that the sensor is supposed to work in a range of 10 - 80 cm, yet on my Bela (also carrying an Audio Expander Capelet) I only get usable data in a range of about 9 to 18 cm. I tested the sensor on a Arduino Uno and then it works as expected. Then I just used the 5v pin of the Arduino Uno and plugged the sensor output into the analog input of the Bela and then it works perfectly. I measured that the 5v pin of the Arduino uno gives me a perfect round 5v, wherein the Bela 5v pin gives me 4.8v. Although the datasheet of the sensor tells me that it is supposed to work with a supply voltage in a range of 4.5 to 5.5 v.
Both the Arduino and Bela are powered right now via a USB hub. For the installations it would be great if I could get a perfect 5v from the Bela to get the IR sensors to work properly. Since the installations will be remote in nature I will be working with 12v car batteries and probably 5v power packs. Any idea how I could solve this?
Thanks in advance!
Sjoerd

giuliomoro

minnowahaw usable data in a range of about 9 to 18 cm

What happens for larger distances? Does Your reading clip at 18cm or does it keep going higher but becoming noisier?

minnowahaw

giuliomoro
Hi Giulio,
When I use the 5v from the Arduino I get readings like this:

voltage : 0.9288125 distance : 32.701516849241 voltage : 1.4955 distance : 18.703506486153 still someone present voltage : 1.47475 distance : 19.012569442132 checking data for 1.5 seconds voltage : 0.684125 distance : 46.809457323278 voltage : 0.70125 distance : 45.47143088067 still someone present voltage : 0.702875 distance : 45.348141694365 checking data for 1.5 seconds voltage : 0.6939375 distance : 46.034001043866 voltage : 0.6931875 distance : 46.092429970398 no one present anymore
Which makes perfect sense: when I remove my body from the prototype the sensor "sees" the wooden wall on the other side ( which is about 45-46 cm away).

When I use the 5v pin from the Bela (that gives me 4.8 where the Arduino gives me 5) I get these readings:
voltage : 2.1165625 distance : 12.444636769232 voltage : 1.7523125 distance : 15.53070403352 still someone present voltage : 0.77625 distance : 40.362272477347 checking data for 1.5 seconds voltage : 0.2635 voltage : 0.0293125 no one present anymore stopped recording data voltage : 0.0271875 voltage : 0.0241875 voltage : 0.033625 voltage : 0.529875 distance : 63.167264411006 voltage : 1.2403125 distance : 23.293540157544 someone present checking data for 1.5 seconds voltage : 1.841875 distance : 14.64864122831 voltage : 0.4045625 still someone present stopped recording data voltage : 0.02675 checking data for 1.5 seconds voltage : 0.0291875 voltage : 0.0265 no one present anymore stopped recording data voltage : 0.028 voltage : 0.03025
So already after 15 cm I get noisy values that jump up to 43 or above (the 63 isn't even possible since the space is about 45 cm wide) and then immediately drop to values close to zero like:
voltage : 0.0271875 voltage : 0.0241875 voltage : 0.033625

minnowahaw

I connected the three wires on the Audio Expander Capelet like this:

And to repeat myself again when I plug GND and 5v into the Arduino Uno everything works perfect... 😕

giuliomoro

That 5V line is not meant to be used for anything that uses any non-negligible amount of current. Get 5V from P9.07 instead and things should improve significantly. It's probably still noisier than the 5V you'd get from Arduino, but it should be good enough for your use case.

minnowahaw

Thanks, Giulio, now it works perfect! It has been a while since I used P9.07, so I had to do a bit of searching to find it, since it's not on the diagram. Thanks again!

minnowahaw

for anyone who is also looking for this secret pin 😉