With my Pololu line following robot I had strange problems with the sensor array: the sensor values were very unreliable. Until I have found the problem: Instead of the expected 3.3V, my FRDM-KL25Z RevD board provided 2.8V instead 3.3V on the P3V3 Arduino header pin:
And that voltage even was lower the more current I needed :-(. Luckily there is an easy hardware fix for this.
Voltage Drop because of Diode D1
The problem is because of Schottky Diode 1: it is causing a the voltage of about 0.5V and even larger for higher currents. So the simple ‘fix’ is to shortcut pin 1 and pin 3 of that diode D1:
That diode D1 is located nearby the KL25Z USB port:
❗ Change the hardware at your own risk. Make sure your power supply is not reverted, and that you only draw a few 100 mA.
With this, the voltage P3V3 is where it should be:
The voltage drop over D1 causes a voltage drop of 0.5V or more, which depends on the current drawn from P3V3. As my sensors on P3V3 need more than 30 mA, the voltage drop was too high to have them operating properly. Short-cutting the D1 diode solved the problem for me and my RevD board.
💡 That problem has been reported to Freescale, and the new RevD boards should have that problem solved. It looks like such RevD boards are shipping now, although my order a couple of weeks ago still had RevD boards.
Happy Shortcutting 🙂