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Topic: 5v Pro Mini and RC 522 RFID (Read 256 times) previous topic - next topic

Chole

I got a 5v ProMini to which I want to connect several RFIDs. The Rfid module is 3.3v, and it says it's not 5v tolerant. What are my options?

Grumpy_Mike

#1
May 28, 2016, 11:36 pm Last Edit: May 28, 2016, 11:37 pm by Grumpy_Mike
Get a 3V3 regulator and drive it off the 5V supply.

Don't forget you will also have to convert your 5V outputs from the Arduino down to 3V3.

aarg

Or get a 3.3V Pro Mini. They're cheap.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

Chole

The arduino will also have to power a 5v relay for a 12v solenoid, so if I buy a 3.3v one I will have to step that up. What about one of those bidirectional level converters, are those easier to use? Can I run 3 Rfid readers through that? Do all pins of the reader have to go through the converter; if so there may be too many pins to use it.

Grumpy_Mike

#4
May 29, 2016, 05:47 am Last Edit: May 29, 2016, 05:47 am by Grumpy_Mike
You can not use logic level converters to power a reader.
You need to use a voltage regulator and capacitors to make a supply to drive the reader.

All the signals bar one between the readers and the Arduino can be in parallel. That is how the SPI bus works. Each reader needs its own enable pin but the rest are common.

You can simply use a potential divider circuit with 1K and 510R on the output pins from the Ardino to the reader. The inputs from the reader can be connected directly.

Chole

Allright voltage regulator + capacitators to go from 5v to 3.3. Which are the arduino output pins on the spi though?

Wawa

The arduino will also have to power a 5v relay for a 12v solenoid.
The Arduino can drive a transistor that can operate the solenoid.
No relay needed, unless you want electrical isolation.
Leo..

Chole

So i am gonna use a 12v supply for the solenoid and the pro mini. Do I connect the power supply to the voltage regulator, bypassing the arduino? Can I use a LM317 regulator?

The Arduino can drive a transistor that can operate the solenoid.
No relay needed, unless you want electrical isolation.
Leo..
I gotta a couple of them laying around doing nothing, to me they seem easier to use.

Wawa

A relay also needs a transistor, a base resistor, and a flyback diode. Same as a solenoid.
Unless you have a relay module with those parts already mounted on the circuit board.
Leo..

Chole

A relay also needs a transistor, a base resistor, and a flyback diode. Same as a solenoid.
Unless you have a relay module with those parts already mounted on the circuit board.
Leo..
They are those 5v 1 or 2 channel module relay shields.

sarouje

#10
May 30, 2016, 06:28 am Last Edit: May 30, 2016, 06:44 am by sarouje
1. From the spec I think Pro Mini can take 5-12v, you add a capacitor to VIN and power the pro mini from your 12v source. I am driving a Nano by directly connecting to a 12v source, it's running 24/7 without any issues. It suppose to drive by LM7809 but I removed because of heat it produced.

2. RFID module, not sure about the current draw. If the current draw is more than Arduino can supply then a regulator is required to convert 12v to 3.3v to power the RFID module. Its better to use a switching regulator, it wont produce much heat.

3. Use a Resistor Voltage divider to connect Arduino TX to RFID RXD. Check the link https://learn.sparkfun.com/tutorials/voltage-dividers

4. Never power a relay module from Arduino, always use the external power. Arduino should only send the HIGH/LOW to the input pin of the relay module. You could also take the Wawa's approach of using a transistor to drive the solenoid. I feel it's better to use a Relay module as you are dealing with Inductive load here.

5. If you are using a 12v relay module then you dont have to stepdown 12 to 5v to power the relay module.


Sony Arouje
http://sonyarouje.com

Grumpy_Mike

#11
May 30, 2016, 09:29 am Last Edit: May 30, 2016, 09:30 am by Grumpy_Mike
3. Use a Resistor Voltage divider to connect Arduino TX to RFID RXD. Check the link https://learn.sparkfun.com/tutorials/voltage-dividers
This, while not being technically incorrect, is wrong. The RFID reader in question does not use serial to communicate, but SPI.


Which are the arduino output pins on the spi though?
All of them with the exception of the MISO pin.

Paul__B

You can not use logic level converters to power a reader.
You need to use a voltage regulator and capacitors to make a supply to drive the reader.
Actually, that first sentence is not quite right!

This - common - level converter actually includes the voltage regulator!


And one RF-522 reader seems to work just fine from the 3V3 terminal on the Nano.

Grumpy_Mike

#13
May 30, 2016, 08:13 pm Last Edit: May 30, 2016, 08:58 pm by Grumpy_Mike
Paul, if you extend the words "logic level converter" to mean a specific logic level converter board that has added regulators then you are indeed technically correct.



I rest my case.

Paul__B

If I have given you "a bit of your own back", then I am satisfied. :smiley-lol:

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