Bus protection

TC

I have a BS2sx that is getting hooked up to a LCD display. I am looking to do bidirectional
Communication between the display and the stamp. And I want to protect both the stamp and the display. I know by putting resistors between the stamp and the display will protect them, but I don’t know what size would work. I do have some 10K sitting around, could they work?
Thanks TC

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We all make mistakes when we are young………That’s why paste is edible!

Mike Green

You want resistors with a low enough value to not affect the signals back and forth significantly, but high enough in value to protect the Stamp pins from a short-circuit to +5V or ground (the most likely mishap). Individual Stamp pins can withstand a current of about 25mA without damage, so R = E / I = 5V / 0.025A = 200 Ohms. A common value higher than this is 220 Ohms which is what is used on the HomeWork board.

10K might work if the LCD has a high impedance input, is close to the Stamp, and isn't running at high speed. You could try it and see if it works, then switch to a lower value later.

Post Edited (Mike Green) : 7/13/2008 6:58:24 PM GMT

TC

thanks I will give it a try

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We all make mistakes when we are young………That’s why paste is edible!