Pololu Robotics & Electronics
My account Comments or questions? About Pololu Contact Ordering information Distributors

3PI robot unusual behavior


Hi All

We have purchased 3PI very recently and It worked well and we used it in exhibition

Anyhow it LCD unit plug in wrong direction at the battery replacement and tried to Power on several time and it does not worked and keep it on a box with battery and next day stated exhibition then only identified that LCD fixed in wrong direction then we re correct it and used it. but from that time the 3PI behavior is unusual. some time follow track and some time going out of track

Next day we reprogrammed the 3pt but problem is remaining same

After week we show it to TV technician who tested it and informed power supply or Transistor to be replaced so we bring it without repair

Dear All please advice to identify the issue

Thanks in advance



I am sorry you are having trouble getting your 3pi robot to work again. Plugging the LCD on the 3pi in backwards would likely damage the LCD, and could possibly cause other damage, though it is not clear that happened here.

Can you post close-up pictures clearly showing both sides of the 3pi so that I can see any signs of damage? Can you use a cheap digital camera (e.g. cell phone camera) to look at the IR sensors while they are on? If the emitters are working, the camera should pick up and display the IR. For details and a picture of what you should be expecting, see the bottom of this page. Please note that some cameras have IR filters on them, so if you do not see any lights, it does not necessarily mean that the LEDs are not working.

- Amanda


Dear Amanda

Thanks for the reply and advice
Please see the attached for both side of 3PI

I checked with my phone camera but I did not see any IR emit from the sensor

Can I have your email address since it does not allow to attached

Please advice



What message are you seeing when you try to attach photos to your post?

You should be able to attach pictures by selecting the “Upload” option (an icon of an underlined arrow pointing up) while you are writing your post. A pop-up window should appear with a choice to upload an image or file from your computer or web; alternatively, you can drag and drop the file directly into the editor.

You mentioned not seeing the IR emitters using the camera on your phone. Can you try using your phone’s front-facing camera (if it has one) to see the IR LEDs?

- Amanda


Dear Amanda

Thanks for the reply and I am really happy with pololu support
As per your advice I checked with front camera so still I did not see the IR light from the camera and I also checked our TV remote controller which is emitting huge IR lights once the button is pressed on remote

Please see the attached picture for you observation

Thanks in advance


Thank you for the posting those pictures. Just to be sure, when you checked for the LEDs, did you have the 3pi powered on (both blue power LEDs should be lit on the 3pi) and the LCD removed? If not, can you remove the LCD from the 3pi, load the 3pi-linefollower example code (again), and verify that the 3pi is powered on before checking for the IR light from the sensors?

There is a MOSFET on the 3pi that is used to turn on and off power to the IR emitters on the line sensors, so if that was damaged, they might all not light. Could you post a clear, close-up picture of that MOSFET (marked by the red circle in the picture below)?

- Amanda


Thanks for the reply

I re upload the line follower code and I observed that both blue LED’s are ON but I did not see Ir lit

Please see the attached picture for your inspection

May I replaced the MOSFET ?

Please Advice

Thanks in advance


I do not see any visible signs of damage on or near the MOSFET, but from your description, it sounds like something is damaged. Please email us with your sales order information and a reference to this thread so we can see how we can help you.

- Amanda


Thanks Amanda

I sent the info to support@pololu.com

Thanks in advance


Hi Hoped you received the info



We got your email and are working with you directly.