m3pi ID12 problem

ID12 RFID reader works fine with just the MBED, pin 14. Using on m3pi, the reader doesn’t work. With m3pi, 14 is not a good choice, for it’s used for LEDS. Pin 10 in not either, for it’s used for serial slave comm. Then, tried 27, and 25. They are both free. Still not work.

Now, all these pins work fine when using USB power for the MBED. But none work when using 3pi battery power, with USB disconnected. The 5 V reader power is from the MBED, for I thought it would OK to hook up there… But, maybe I need to connect it to 3pi battery power?



Can you provide a link to some documentation for your ID12 reader and to any existing mbed resources for it?

- Ben

Hi Ben,

Got RFID to work on m3pi. I made error thinking pin 2 of mbed was 5 volts out. It is true when powered from PC USB, but not when 3pi is power source. Connected the ID12 to VCC on expansion board that goes to battery on 3pi. All is well. The RFID ID12 is from Sparkfun. I have it mounted on the m3pi, where a Wixel might go. When I swipe a RFID card over ID12, the 3pi moves. Starting is still done as normal with push button. Another routine from mbed is Timeout. I use it to do a turnaround at halftime and stop at fulltime. I still have the Sharp distance sensor to sense an obstruction and turn around.

Tonight I figured out how to shut down power completely when stopped, not pushing the button. I use a 4N25 opto isolator. Pin1 goes to a mbed digital output pin, pin 2 goes to mbed ground. Pin 4 goes to left side of push button, pin 5 goes to right side of push button. The 4N25 gives great isolation. So, at the end of the 3pi run, the last statements of the program makes an mbed pin go high for 0.25 seconds to the 4N25. The output shorts around the push button, which which kills battery to the robot.

Here is info on the ID-12.

The 3pi is still amazing. Laid off of it for a couple years, but back at it with mbed and your expansion board.
Also, added 3 RGB LEDS that change color every few seconds. Found a piece of cut up USB cable with plug still on it. Found 5 volts. Stuck a RGB LED on top, then plugged into vertical USB on expansion board. It’s like a 3" antenna, and looks neat. Balance of 3pi getting a bit front heavy. Slid a couple of large nuts over the “antenna” Holds rear end down, sort of like spoiler action.

Now, I want to pull a little 2 wheel plastic trailer with mp3 device and speaker and a couple more LEDS. Do you have such a “cargo carrier”? Of course spinning would not work very well! So, maybe not very realistic.

Happy Holidays to you and all at Pololu


It sounds like you are doing some really cool stuff with the m3pi! Thank you for sharing your projects with us so far, and I hope you will continue to do so. Unfortunately, no, we don’t have any sort of “cargo carrier” for the 3pi/m3pi, but I’d love to hear about it if you make one. Happy holidays to you, too.

- Ben