Electronic – arduino – Are these two Arduino Pro Micros jumpered correctly

arduinoidentification

I picked up a couple of cheap Pro Micro's off eBay a while back. Both are blue, and have no brand identifier on them (ie, Adafruit, Sparkfun, etc.). The ebay ad. directly copies the text from SparkFun's Pro Micro – 5V/16MHz product page, where I got the schematic.

My challenge here is that I couldn't seem to get them to be identified by the IDE, so I'm trying to figure out just which they are. I know they are Pro Micro, but still not sure about the 3.3V vs. 5V part.

Here's a summary of what I know…

The product description says 5V
The boards are marked "V11"
The voltage regulator on the board is a mic5219 labeled LG50 (which is 5v)
The spot on the back where one can mark "5V" or "3.3V" on the circuit is not marked
The schematic states for the jumper "Closed for 5V version"
The J1 jumper is NOT bridged, which would imply it's configured for 3.3V (?)
The main chip is an ATMEL MEGA32U4.

So there's the quandry. 5V regulator, but J1 not bridged as for 3.3V? 3.3V?

Here are some photos…
The two boards
Closeup of un-bridged J1 and voltage regulator (LG50, a 5V one)
Back of board showing unmarked 3.3V/5V and V11

Any suggestions on how I can precisely identify the boards or at least know if they in fact are 5V but should have J1 bridged? It seems based on the voltage regulator that it's 5V, but then J1 should be bridged if this was the case.

Best Answer

At a glance, the operating frequency of the XTAL on board may tell the operating voltage of your Arduino.

If the XTAL is 16MHz, the device is probably 5V. If the XTAL is 8MHz, the device is probably 3.3V.

Make sure to use a multimeter and trace the power pins to the jumper / LDO. Also measure voltage at LDO output to see if LDO is active or not.

Related Solutions

Electronic – Help with device identification in a chain

It would help to know what phy layer you're using. But, here's some general information:

If you're using I2C, your bus should look something like this:

(taken from societyofrobots.com)

At runtime, you can detect the I2C addresses by scanning the bus by sending a START condition to every address and checking for an ACK.

If you're using SPI, you'll need a chip select line per device. If you run out of pins, you could use some kind of multiplexer. You may be able to scan the bus by asserting each chip select line in turn and attempting to communicate.

http://kkamagui.springnote.com/pages/422905/attachments/177111

Electronic – Arduino: better microsecond resolution than micros()

Yes, depending your Arduino's basic clock rate. For example here are the counter-timer input frequencies and periods after pre-scaling, for an ATMega2560's counter-timer 2, and a basic clock rate of 16MHz. The timer has built in "prescaler" value options which determine frequency/period, shown in this table:

    TCCR2B bits 2-0    Prescaler    Freq [KHz], Period [usec] after prescale
          0x0          (TC stopped)      --         --
          0x1                1        16000.        0.0625
          0x2                8         2000.        0.500
          0x3               32          500.        2.000
          0x4               64          250.        4.000
          0x5              128          125.        8.000
          0x6              256           62.5      16.000
          0x7             1024           15.625    64.000

For better timing resolution, you use a value called TCNT2. There is build in counter that goes from 0 to 255 because the timer is 8 bit. When the counter reaches the value assigned by TCNT2 it triggers an interrupt. This interrupt is called TIMER2_OVF_vect.

given this information, the resulting interrupt rate would be: 16MHz / (prescaler * (255 - TCNT2))

You could get the timer to run at the full 16MHz (62.5nSec) though that's way faster than you need; 2MHz with an initial count of (255-2) would give you 1MHz interrupt rate. Divide that by 2 in your ISR:

extern uint32_t MicroSecClock = 0;

ISR(TIMER2_OVF_vect) {// this is a built in function that gets called when the timer gets to the overflow counter number
  static uint_8 count;            // interrupt counter

  if( (++count & 0x01) == 0 )     // bump the interrupt counter
    ++MicroSecClock;              // & count uSec every other time.

  digitalWrite(53,toggle);// pin 53 is arbitrary
  TCNT2 = 253;                    // this tells the timer when to trigger the interrupt. when the counter gets to 253 out of 255(because the timer is 8 bit) the timmer will trigger an interrupt
  TIFR2 = 0x00;                   // clear timer overflow flag
};

The data sheet for your MCU is the basic resource; this article will give you (and gave me!) a good head-start.

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