Electronics > Beginners
Confirmation and Clarification
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King_bob:
I designed a circuit with and Arduino Pro Micro (5V), and 2xADNS3050 (optical mouse sensors, 3.3V) and a bunch of other stuff. Now I am trying to optimize the circuit, to free up an extra pin as well as use one 4-channel-3.3v-to-5v-logical-level-shifter less. To do this I bundled the Motion pins of the ADNS3050 and connected these, as well as MISO, directly to the Arduino, as is visible in the image below:
My first question is, Is it OK to attach the MISO from 3.3v to 5v directly without damaging the 3.3v source? My understanding is that since the ADNS3050 is the Slave and MISO stands for "Master In Slave Out", the Slave sets 3.3v to the connection, which is still fine for the Arduino. Are there any negative aspects to doing this, if it is possible?
Secondly, the Motion Pins from the ADNS3050s act as an Interrupt (they go to pin 7 on the Arduino, which is the only leftover interrupt pin that I have) Would bundling them cause any issues? My guess is the same as for MISO as to why these are directly connectable to the 5v Arduino, but if this is not the case I would welcome a heads up.
I do also have a coding question, but Ill dump that elsewhere.
Thanks.
mariush:
Do you actually need that level shifter, considering you can run the atmega chip with 3v on the i/o?
See pages 255-256 in datasheet : https://cdn.sparkfun.com/datasheets/Dev/Arduino/Boards/ATMega32U4.pdf
You have the schematics of the Arduino Pro Micro on Sparkfun's website so you could desolder some components or cut a trace with a sharp blade if needed.
King_bob:
Yes, I considered this as well, but I have an OLED display (i2c), as well as a fingerprint reader(RX/TX) that runs on 5 volts as well... And I am not certain but isn't the speed of the chip only 8Mhz at 3.3v? I do not know if or even how this would effect a mouse-ish input device... Most computer mice that I found run with 38 to 40Hhz chips, so 16Mhz is already lower than the norm. Of course I may be completely wrong in the assumption and 8Mhz may be fine, but either way Id have to use at least one 4 ch shifter, so I figure sticking with 5v should be better.
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