# i2c amplifier

**URL:** <https://community.sparkfun.com/t/i2c-amplifier/24815>\
**Category:** Arduino\
**Created:** [August 16, 2012, 1:51am UTC](https://community.sparkfun.com/t/i2c-amplifier/24815 "2012-08-16T01:51:53Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![Seawolves\_ROV](https://avatars.discourse-cdn.com/v4/letter/s/8baadc/32.png) [@Seawolves\_ROV](https://community.sparkfun.com/u/Seawolves_ROV)\
**Post date:** [August 16, 2012, 1:51am UTC](https://community.sparkfun.com/t/i2c-amplifier/24815/1 "2012-08-16T01:51:53Z")

</div>

I’m trying to get i2c from an expander chip to an Arduino Mega over a 100ft twisted pair. What would I use to amplify the signal (I have tried with no amp and the signal doesn’t make it). I have a maximum of 12v DC to work with. :think:

---

<div class="post-metadata">

**Author:** ![phalanx](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/phalanx/32/3698_2.png) [@phalanx](https://community.sparkfun.com/u/phalanx)\
**Post date:** [August 16, 2012, 11:21am UTC](https://community.sparkfun.com/t/i2c-amplifier/24815/2 "2012-08-16T11:21:22Z")

</div>

I’m not sure of the maximum distances possible but have a look at these: [http://www.nxp.com/documents/leaflet/75016081.pdf](http://www.nxp.com/documents/leaflet/75016081.pdf)

Besides dedicated buffer ICs, you can increase the current on the I2C bus as well as reduce the bit rate to get ~~higher speeds~~ longer bus lengths.

-Bill

---

<div class="post-metadata">

**Author:** ![KeithB](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@KeithB](https://community.sparkfun.com/u/KeithB)\
**Post date:** [August 16, 2012, 7:13pm UTC](https://community.sparkfun.com/t/i2c-amplifier/24815/3 "2012-08-16T19:13:23Z")

</div>

Reduce the bit rate to get higher speeds? how does that work? 8^)

---

<div class="post-metadata">

**Author:** ![phalanx](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/phalanx/32/3698_2.png) [@phalanx](https://community.sparkfun.com/u/phalanx)\
**Post date:** [August 16, 2012, 7:33pm UTC](https://community.sparkfun.com/t/i2c-amplifier/24815/4 "2012-08-16T19:33:21Z")

</div>

> KeithB:  
> Reduce the bit rate to get higher speeds? how does that work? 8^)

If it’s not working and you reduce the bit rate until it starts working, your actual throughput is higher than what you had before. That’s my explanation and I’m sticking to it!

---

<div class="post-metadata">

**Author:** ![KeithB](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@KeithB](https://community.sparkfun.com/u/KeithB)\
**Post date:** [August 16, 2012, 8:10pm UTC](https://community.sparkfun.com/t/i2c-amplifier/24815/5 "2012-08-16T20:10:41Z")

</div>

I was actually going to add, “do you make it up in volume?” 8^)

---

<div class="post-metadata">

**Author:** ![Seawolves\_ROV](https://avatars.discourse-cdn.com/v4/letter/s/8baadc/32.png) [@Seawolves\_ROV](https://community.sparkfun.com/u/Seawolves_ROV)\
**Post date:** [August 16, 2012, 10:22pm UTC](https://community.sparkfun.com/t/i2c-amplifier/24815/6 "2012-08-16T22:22:46Z")

</div>

I’ll try the amp first because I do hardware better than software, but I’ll look into both. Thanks.

---

<div class="post-metadata">

**Author:** ![Dave\_Mueller](https://avatars.discourse-cdn.com/v4/letter/d/ed8c4c/32.png) [@Dave\_Mueller](https://community.sparkfun.com/u/Dave_Mueller)\
**Post date:** [August 17, 2012, 11:01pm UTC](https://community.sparkfun.com/t/i2c-amplifier/24815/7 "2012-08-17T23:01:26Z")

</div>

For most digital communications, it’s always a trade-off of speed versus distance. I think RS485 is spec’ed for 4000m but only at 9600bps. Speed it up to 115.2Kbps and the distance goes way down. And that’s ignoring protocol timing for things like a NACK.