# Arduino Ethernet W5100 minimal circuit **URL:** \ **Category:** General Electronics\ **Created:** [October 3, 2013, 12:38pm UTC](https://forum.arduino.cc/t/arduino-ethernet-w5100-minimal-circuit/186520 "2013-10-03T12:38:10Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![martin159](https://avatars.discourse-cdn.com/v4/letter/m/ce73a5/32.png) [@martin159](https://forum.arduino.cc/u/martin159)\ **Post date:** [October 3, 2013, 12:38pm UTC](https://forum.arduino.cc/t/arduino-ethernet-w5100-minimal-circuit/186520/1 "2013-10-03T12:38:10Z")
Hi, I am using Arduino with 8MHz internal crystal. I do not need any other electronic parts, only ATmega and power supply (7805). There is working schematic: [http://todbot.com/blog/wp-content/uploads/2009/05/minimal-arduino.png](http://todbot.com/blog/wp-content/uploads/2009/05/minimal-arduino.png) I have about 5 working cirtucits based on this schematic that works more than one year without error. Now I need add Ethernet. I would like to buy officialy supported Wiznet [W5100](http://cz.mouser.com/ProductDetail/WIZnet/W5100/?qs=b%252bXOOdUOuvb5w6ehtacQUw==). (For testing I was bought original shield.) Can you please help me how can I connect W5100 to ATmega328 with minimal other parts? I was looking into official Arduino Ethernet Shield schematic, but it is big complicated to me: [http://arduino.cc/en/uploads/Main/arduino-ethernet-shield-06-schematic.pdf](http://arduino.cc/en/uploads/Main/arduino-ethernet-shield-06-schematic.pdf) I do not need SD card reader or any other device. Only Ethernet. Is it neccesarry to use [H1012NL](http://cz.farnell.com/pulse/h1012nl/module-transformer-ethernet/dp/2113972) transformer (or similar) and connect RJ45 socket to W5100 through this transformer? Is it possible to buy RJ45 socket with integrated protection? Or how it works on original shield? I can't use original shield because is to big and I need small and manufacturable board. If it is important I can put 16MHz external crystal to ATmega. I found a lot of minimal schematics for ENC28J60 but not for W5100 ☹ Thanks for help. ---
**Author:** ![JChristensen](https://avatars.discourse-cdn.com/v4/letter/j/e9bcb4/32.png) [@JChristensen](https://forum.arduino.cc/u/JChristensen)\ **Post date:** [October 3, 2013, 12:51pm UTC](https://forum.arduino.cc/t/arduino-ethernet-w5100-minimal-circuit/186520/2 "2013-10-03T12:51:42Z")
> martin159: > Can you please help me how can I connect W5100 to ATmega328 with minimal other parts? I was looking into official Arduino Ethernet Shield schematic, but it is big complicated to me: [http://arduino.cc/en/uploads/Main/arduino-ethernet-shield-06-schematic.pdf](http://arduino.cc/en/uploads/Main/arduino-ethernet-shield-06-schematic.pdf) Well, that's pretty much how it's done. Compare that to what's in the [W5100 datasheet](http://www.wiznet.co.kr/UpLoad_Files/ReferenceFiles/W5100_Datasheet_v1.2.4.pdf). I've also used the [WIZ811MJ](http://www.wiznet.co.kr/sub_modules/en/product/Product_Detail.asp?cate1=5&cate2=42&cate3=0&pid=1030) and [WIZ820io](http://www.wiznet.co.kr/sub_modules/en/product/Product_Detail.asp?cate1=5&cate2=42&cate3=0&pid=1161) (W5200) modules. Unless we're talking considerable volume, those modules may represent a better choice. If you are really bent on rolling your own, then it sounds like you will have a learning curve. ---
**Author:** ![martin159](https://avatars.discourse-cdn.com/v4/letter/m/ce73a5/32.png) [@martin159](https://forum.arduino.cc/u/martin159)\ **Post date:** [October 3, 2013, 1:09pm UTC](https://forum.arduino.cc/t/arduino-ethernet-w5100-minimal-circuit/186520/3 "2013-10-03T13:09:47Z")
> [@](#): > > Well, that's pretty much how it's done. Compare that to what's in the [W5100 datasheet](http://www.wiznet.co.kr/UpLoad_Files/ReferenceFiles/W5100_Datasheet_v1.2.4.pdf). I've also used the [WIZ811MJ](http://www.wiznet.co.kr/sub_modules/en/product/Product_Detail.asp?cate1=5&cate2=42&cate3=0&pid=1030) and [WIZ820io](http://www.wiznet.co.kr/sub_modules/en/product/Product_Detail.asp?cate1=5&cate2=42&cate3=0&pid=1161) (W5200) modules. Unless we're talking considerable volume, those modules may represent a better choice. If you are really bent on rolling your own, then it sounds like you will have a learning curve. WIZ820io looks good but it is too [expensive](http://cz.mouser.com/ProductDetail/WIZnet/WIZ820io/?qs=b%252bXOOdUOuvZr7ySTpTRyJw==) (about $25). But I found schematic on web. Thank you 🙂 If I use RJ45 socket with integrated transfromer, It looks simply: [http://www.wiznet.co.kr/Admin\_Root/UpLoad\_Files/BoardFiles/WIZ820io\_Schematic\_V1.0.pdf](http://www.wiznet.co.kr/Admin_Root/UpLoad_Files/BoardFiles/WIZ820io_Schematic_V1.0.pdf) [WIZnet - IoT Network Accelerator](http://www.wiznet.co.kr/Admin_Root/UpLoad_Files/BoardFiles/WIZ820IO%20Rev1.0%20Partlist.pdf) ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [October 3, 2013, 7:20pm UTC](https://forum.arduino.cc/t/arduino-ethernet-w5100-minimal-circuit/186520/4 "2013-10-03T19:20:15Z")
This is all deja-vu to me. I have the Ethernet shield, I have a few of the WIZ modules, and I'm sourcing parts to begin a home-brewed W5100 design. Yes, you'll need integrated magnetics. One of the Pulse MagJack connectors will work. Get one for 10/100 with auto-MDIX support. (This ensures the xformer etc. are all symmetric so the RX pins work as TX and vice versa.) ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [May 6, 2021, 1:25am UTC](https://forum.arduino.cc/t/arduino-ethernet-w5100-minimal-circuit/186520/5 "2021-05-06T01:25:41Z")