I have a few questions about converting 5v to 3.3v.
I have a network monitoring project using an Arduino Pro Mini (5 volt version), an ENC28J60 internet module, and an i2c LCD screen. Please see the attached files circuit.jpg and closeup.jpg.
Originally the project was going to be completely 5-volt, but the ethernet module "appears" to require 3.3v; I will come back to this later in the post.
I have a LM 1117 T3.3 voltage regulator and am planning on using it in conjunction with two 10k resistors (labeled A and B in closeup.jpg) and a 10v 22µF capacitor (labeled C in closeup.jpg).
In laying out the circuit, I began wondering if anything more could be done with regard to regulating the voltage. After searching this topic, it seems there are probably 20 different ways one could regulate voltage!
Are there any big shortcomings using the 10k resistors and the 10v capacitor as mentioned earlier and shown in the attached images? Am I missing anything in the voltage regulation circuit as shown? Can you recommend anything extra that could be added to the voltage regulator circuit, or any changes to the resistors or capacitor values?
The logic driving the ethernet module will be from the 5v Arduino. Do I need to put anything between the Arduino and the ethernet module?
Now, to get back to the ethernet module. I got this module from a large electronic supply company. In one section of the pdf instructions, it clearly states that VCC is for a 3.3v power supply. However in the very next section, the user is instructed to connect the VCC pin the to 5v pin of the Arduino (See instructions.pdf).
I’m not sure if this is just a sloppy cut and paste error or if the module will indeed tolerate 5 volts. A search suggests that the ENC28J60 chip itself might be tolerant of a 5v supply, but what about the other components on the module? Does anyone have any thoughts on this? I will contact the company on Monday, but I doubt that it will be able to speak with someone knowledgeable. instructions.pdf (381.2 KB)
I've not heard of using resistors with a fixed regulator. What's the point?
You have input, ground, output, just a 100uF electrolytic cap from 5v to Gnd, and 10uF electrolytic cap from 3.3v to Gnd, both near the regulator. (or 10uF and 1uF if the current load is low). Resistors are not needed.
It looks like you do need to use Vcc of 3.3, wherever you get that - some Arduino are 3.3 volt, others have a 3.3 volt output available or use the regulator like you drew.
edit: if you use a board’s 3.3 volt source, make sure it can handle the current required.
The good news is the 5V tolerant inputs, which means you will not need level shifters on the logic lines.
You may want to google for yourself a bit and get your own read or otherwise confirm before blowing anything up, but that’s my mine.
The manufacturer or whomever you want to speak with should know at least this much one would hope.
If in the future you find you require a 3.3v supply and choose the same regulator.
The two 10K resistors are an incorrect usage of the regulator device.
That lead must go the the 5V ground. AND you must have a capacitor at the input of the regulator and at the output of the regulator. I think the input is between 1 & 10µF but check your datasheet for the recommended value.
The reason for these capacitors is the regulator is really an amplifier with an input of 5V and an internal reference or 1.25 volts. With any amplifier the possibility to oscillate is always a concern.
As you were told above, the ENC28J60 module requires 3.3V supply voltage (3.1V to 3.6V).
If you have a 3.3V regulator, it doesn't need resistors, only capacitors.
The LM1117 Datasheet says
An input capacitor is recommended. A 10-μF tantalum on the input is a suitable input capacitor for almost all applications.
The minimum output capacitance required by the LM1117is 10 μF, if a tantalum capacitor is used.
I did an Arduino project several years back and kept some spare parts from the project. Unfortunately, the only capacitors I have available are 22µF and a 100µF. I hadn't planned on ordering anything else from the electronic supply company for the foreseeable future, and its really not worth spending 8 Euros just on delivery for a couple of 50 cent capacitors.
As a more practical alternative, I have found this voltage regulator on Amazon. The regulator uses an AMS1117. Would this be a viable all-in-one solution that wouldn’t require any further capacitors? It has some smd components on the board, but the data sheet doesn’t fully clarify these. What do you all think?
Well, yes, but only for the moment. Why is buying those preferable to buying capacitors?
Those modules include the capacitors.
I think you need to sit down and plan ahead in order to order a quantity of capacitors (and other components such as resistors) suitable for your planned future products.
My last Arduino project was several years ago, and I doubt that I will have much spare time for projects going forward, but when I do, it would be worth making a thorough list of useful items!
Anyway, thanks for your input, I appreciate your time!
Looking at the photo, we can say that the module has two capacitors (10μF and 0.1 μF) at the input and at the output.
If this is true, it can be used.
Just the small size of the capacitor is in doubt.
