Sense check on DIY ioio sheild

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Andrew Robinson

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Jun 21, 2015, 3:11:49 PM6/21/15
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Hi all

Can anyone give this board design a quick once over to see if I have the right idea on pull-up resistors. 

My 2 sided pcb board will sit above a Dagu 4 channel H-bridge motor controller, and the IOIO-OTG will then sit on top of that, using a sandwich of 0.1 pitch female/male pins.

Having read a blog about using servos with ioio I am concerned I have understood Mitcech's diagram, and wired up the pull-up resistors correctly (R2 and R3), I use pins 13 and 14 to drive PWM to the servo, and these pins are also connected to +5v.

Can anyone see any fault with what I have tried to do here, or is this ok? (I have gray scaled other features of my board, to illustrate the parts of the circuit Im discussing in this question, hope it helps explain)

Thanks for any input.

Andy






LK1000TEST.png

Ytai Ben-Tsvi

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Jun 24, 2015, 10:46:50 PM6/24/15
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It's fine. What I normally do is pull the control line down to ground and use the pins in push-pull (normal) mode. Your setup is useful if you want to operate in open drain mode to generate a 5V signal. In practice, I've never seen a servo that minds feeding off of a 3.3V control signal. Pulling the control line one way or another also serves the purpose of asserting a known state on the pin when the IOIO floats the pin, e.g. when your app is not running. Otherwise the servo may twitch.

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