Propeller 3.3v to BiStep USB 5.0v logic

WebheadFred

Hello Folks,
First of all, I'd like to thank all of you for a great forum. I have learned much in the few months I've been on. I've decided on the Propeller and have started working through code getting up to speed. I've built a duel power supply (3.3 and 5.0) and the propeller is working perfectly. I have managed to connect it the the 4x20 LCD backlight display and it works perfectly. I am about to connect to the BiStep motor controller. After reading more and more, I thought I'd ask this question before I messed everything up newbie style. As all of you know, the prop is 3.3v, the BiStep is 5.0. My power supply handles all this of course. I can communicate to the LCD Rx pin directly from one of the pins on the Propeller. My question is; since the BiStep is a 5v system, I'm anticipating problems if I do anything other than transmit data to the device. If I were to receive data from one of the report commands, I'm thinking some sort of conversion is needed or I'll torch the Propeller. Am I right here? Thanks for any feedback.

Best Regards,
Fred

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Why be one if you can't act like one? Knoxville, TN

Bobb Fwed

Simple answer is to put a 1K or 2K resistor between the Prop and the 5V device that is transmitting to the Prop. There is a diode in the Prop that dumps voltage higher than 3.9V (or so), but it has a current limit. Thus the resistor. I've used 1Kohm resistors without problems, but people have recommended 2Kohm or 2.2Kohm (is more common). Higher resistance shouldn't ever be a problem unless the communication speed is really fast.

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April, 2008: when I discovered the answers to all my micro-computational-botherations!

WebheadFred

Thank you very much. This is exactly what I was looking for.

Fred

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Why be one if you can't act like one? Knoxville, TN