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Topic: 5v Pro Mini and RC 522 RFID (Read 4795 times) previous topic - next topic

jumpjack

I used a voltage divider to get 3.3V from 5V of my ProMicro (compatible), but when I connect the  3.3V to the logical converter which joins arduino and RC522, the voltage on the pin drops to 1.2V, why?
Then I changed the divider to get 3.3V also when connected: the RC522 gets powered... but is not working anyway; if I power it from the 3.3V of another arduino, it works fine.

In a second instance, why can't I use the logical converter also to power the RC522?

Grumpy_Mike

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In a second instance, why can't I use the logical converter also to power the RC522?
Because logic level converters are high impedance and not designed to supply more than a few mA.

 
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converter which joins arduino and RC522, the voltage on the pin drops to 1.2V, why?
You talk about a voltage converter and the a potential divider, is this the same thing?
What resistors are you using 510R and 1K are the values I use.

Netoperz

This is old topic, but i hope it helps some people in future.
Just to clarify things that are not clear:

1. I'm making and selling readers based on RC522 and Pro-Mini, and they work in restaurants 3 years without even one returned for warranty.

2. If you really must use Pro mini, but as the price per unit is not very high i suggest using Pro micro that is atmega 32u4 based and 3.3v already.

3. You can use 5V pro-mini without problem, and you do not need voltage level converters or voltage level dividers for spi connection to RC522 !! read the spec of RC522 and atmega328 !

RC522 data lines are 5V tollerant, and also the data line signals from 3.3v logic are fine for 5V atmel to be accepted and properly recieved.

The only problem is powering the rc522... The data lines are 5v tolerant, but the VCC to power the rc522 should be 3.6V max (datasheet)

So you should use simple voltage regulator for converting the power delivered to the RC522, powering it from the regulator that is on board will cause resets due to the power hungry rc522, so get the power source from the RAW pin than use regulator for 3.3v output and that should power the rc522, and that's the only think you should do to connect RC522 to 5v arduino.

And one last thing... You can power the RC522 with 5V ;) on your own risk. It works for me, but the RC522 is a bit warm, might need some heat-sink. In my case none of the RC522 modules had no harm when i have used 5V to power, but this is not official advice. Do it on your own risk. The plus of that solution is that the reader module has got better range, and can easily power the VISA cards (that have got smaller antennas and not always are properly initiated when the module is in 3V) with mastercard no problems, they mostly work same way as standard tags.

Hope that helped.

And remember that programming the arduino pro-mini needs connecting 5 lines TX RX GND VCC and RST (rst should be connected to the RTS line of programmer, and there should be 0.1uF ceramic capacitor between (code 104)   just like this  arduino pro-mini RST ------||------RTS Progaming interface.

Some people are forgetting about it and have some headache when the first time can upload the sketch and second time not :)

 

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