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Asked — Edited
Resolved Resolved by Rich!

Do I Need Resistors


My MMA7455 Accelerometer finally dropped through the letterbox today, thank goodness. But now I have a question. A few i2c examples have shown that resistors are needed. Some didn't.

Do I need them or are they optional. If they are optional, what are the benefits?

Using this one http://www.tandyonline.co.uk/mma7455-accelerometer-module.html although bought from elsewhere. Please note that I will be using a compass as well if it ever arrives.

The guy at tandy says that they already have pullup resistors in it if that means anything


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Nope, resistors are not necessary, at least not on mine:)

Have a read through my post, it covers a lot as I was having problems (turned out to be a bad jumper wire).
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cool means I can start testing now
Hey! Rich is right and the resistors are not necessary. The MMA7455 connects to the EZ-B by the i2c interface. The 4 wires are Gnd, +5, SDA and SLC - and they connect to the respective MMA7455 ports, but it sounds like you got it under control:)

The pull-up resistors are used to help protect the MMA7455 from getting too much voltage. If they didn't have that you would want to get a logic level shifter.

How is the testing going?
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It all depends on the I2C device used. I have read that some compass modules need pull up resistors before they will work, but so far none of the I2C devices I use have needed them (MMA, LCD, PWM driver and a few other bits).

However, as I mentioned in another topic or two, I have an I2C board I knocked up, it's just a bunch of pin headers joined together for easy connection of devices. On the board I have left space for pullup resistors if they ever do become required.

Excuse the poor photo, I'm too lazy to grab the camera and put the memory card in the PC so used the phone instead.

User-inserted image

The red box should highlight the area that 2 pullup resistors could be added if needed. And yes, I know it's a lot of pin headers, I don't plan to use them all but it's future proof:) I have a smaller one in Jarvis

Thanks for the explanation Geoff, I knew where they go but had no idea what they did:)
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testings going quite well. just a trying to get it to correctly realign a pair of biped legs when pushed or falling. already have it communicating with a simulator