This schematic doesn't work, but I have no idea why.

I am trying to make a board that has an Arduino and an ethernet shield all built in to one. The arduino part works fine, but I can’t get the ethernet to work. I’ve attached my schematic. Measuring the pins, The ENC28J60 is receiving 4.3 volts instead of 3.3. I can’t figure out why, though. I should note that I’m powering it purely off the FTDI port, even though I soldered on the regulator.

Edit: I tried removing the 5V regulator, nothing has changed. I also felt the 3.3V reg, it’s warm to the touch, but not so hot it burns.

laptopdude90:
I am trying to make a board that has an Arduino and an ethernet shield all built in to one.

But why would you want to do that?

It is difficult to read that schematic, but it looks like you are applying 5V signals to the inputs of a 3.3V chip, without using level converters. That is a very bad idea. Instead, run the ATmega at 3.3 V.

Among other possible problems, the requisite caps appear to be missing from the regulators.

Paul__B:
But why would you want to do that?

It only costs $15 to make my own. I have some other reasons that I don't want to get into.

jremington:
It is difficult to read that schematic, but it looks like you are applying 5V signals to the inputs of a 3.3V chip, without using level converters. That is a very bad idea. Instead, run the ATmega at 3.3 V.

Among other possible problems, the requisite caps appear to be missing from the regulators.

I've got a logic shifter in there between the atmega and the ENC.

What are requisite caps?

You have nothing buffering SCK, MOSI, and CS going to the chip. The chip does have 5V tolerant inputs.
Check your regulator, which you don’t show a number for.
It is likely miswired, or it needs an input or output cap for stability.

In addition to posting an image of the schematic, the actual schematic file from EAGLE would be nice. It would make it much easier to evaluate the circuit.

What is the 3.3V (and 5V for that matter) regulator you are using? What value decoupling capacitors are being used?

CrossRoads:
You have nothing buffering SCK, MOSI, and CS going to the chip. The chip does have 5V tolerant inputs.
Check your regulator, which you don't show a number for.
It is likely miswired, or it needs an input or output cap for stability.

Regulator isn't miswired. There isn't any input or output caps, I didn't know they were needed. I'll add them later today.

I don't think I'll bother uploading the schematic, I think we're close to solving it.

What's a decoupling capacitor?

There's a total lack of decoupling capacitors anywhere - suggest you look at the
datasheets for each chip to see what values are recommended, in the absence
of this information assume:

1uF on input to regulator
33uF on output of regulator
0.1uF ceramic on every power pin of every other chip, close to the pin.

The reason you may think you're seeing 4.3V on the regulator output is that
its oscillating at high frequency, possibly damaging its load. Regulators in general
require a certain minimum output capacitance to be stable.

MarkT:
There's a total lack of decoupling capacitors anywhere - suggest you look at the
datasheets for each chip to see what values are recommended, in the absence
of this information assume:

1uF on input to regulator
33uF on output of regulator
0.1uF ceramic on every power pin of every other chip, close to the pin.

The reason you may think you're seeing 4.3V on the regulator output is that
its oscillating at high frequency, possibly damaging its load. Regulators in general
require a certain minimum output capacitance to be stable.

Thank you! I'll prototype a new version on my breadboard when I get more parts. Hope this fixes it!

Hi, can you tell us what your experience level is?
Program wise.
Electronics wise.
Hardware wise.
I find it difficult to see you designing PCBs and not knowing about capacitiors and regulators and bypassing.
Have you got a DMM to measure circuit parameters? A regulator just getting warm is not really enough.
How much current is it conducting and what is the input and output voltages measured?
Is the PCB a homebrew or commercial prototype board?

Tom...... :slight_smile:

@Tom: the title of the post was appropriately chosen.

Hi jremington, just trying to see if we have established a new baseline for noob..

Laptop, we can see you are trying to get a project going, but it seems as though you need to start with a more basic project, and work towards this.

Can you post a picture of your project, and a graphic of your PCB pattern.

Tom..... :slight_smile:

Hi, Tom:

Perhaps a new baseline indeed, but one has to admire the self confidence!

Cheers, Jim

Which 3.3v regulator are you using? Do you need an input higher than 5V for it to maintain regulation. Some regulators (and dc-dc convertors) require a couple of volts more on the input.

I agree with the other posters that a few caps are in order.