Let's Make Robots!

How do I connect a 5V sensor to a 3.3V input


I am using a IR sensor (photo transistor) that was ripped out of a ball mouse and I am running it at 5V, but I need to connect it to a Raspberry Pi which runs at 3.3V (at least the IO-pins are). 

I can place a 3.3V regulator before the sensor and adjust the pull down resistors, or use a zener diode to limit the output, but I was wondering wheter my currecnt setup will be safe to use.

Sorry for the poor quality drawing by the way.

Relay vs H-bridge question

most of the time I use an L298D motor driver IC for controling motors. However i find that the 1+ voltage drop is anoying. Some motors just dont go fast enough. 

Using a 7.2V power supply, leaves about 6V going to the motors and, as I understand it, the L298D is not designed to take in higher voltages. Although I think it can handle quite a bit if you cool it properly.

Dont keep your inputs floating!!!

I keep hearing and reading about the importance of making sure all the unused inputs are pulled low with a resistor. No reason is given other than "don't keep them floating because you'll get unpredictable results!"

If you take a look at the picaxe 28X board, you see that all the digital inputs are pulled low with a 10K resistor. I understand that this makes it easier to just connect a switch to the pins on the board without having to add an external resistor. The analog inputs are left floating, almost as if by design.

hardware not found error


I run the picaxe programming editor on windows XP in a virtual machine (parallels desktop) on my OS X laptop. The serial connection to the picaxe 28x1 works fine when I'm just communicating using hyperterm or when the picaxe sends debug info.

When I want to upload a program to the chip, it usually takes 4 or 5 tries to get it right. The larger the program, the more it fails to load.

So i decided to use the command line compiler for mac OS X. Now the uploads are very stable only a new problem appeared.