Why is Aref connected to Vcc on a breadboard Arduino

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bebo
 
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Why is Aref connected to Vcc on a breadboard Arduino

Post by bebo »

I've read that you shouldn't connect Aref to a voltage unless you specifically set it up in the setup() loop (analogReference(EXTERNAL)), otherwise the chip might get shorted out and badness will ensue. Why does the image on the Arduino page show both the Aref and AVcc pins connected to +5V?

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Franklin97355
 
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Re: Why is Aref connected to Vcc on a breadboard Arduino

Post by Franklin97355 »

According to that page:
Start by connecting a 10k ohm pullup resistor to +5V from the RESET pin in order to prevent the chip from resetting itself during normal operation. The RESET pin reboots the chip when pulled down to ground. In later steps we will show you how to add a reset switch that takes advantage of this.
Pin 7 - Vcc - Digital Supply Voltage
Pin 8 - GND
Pin 22 - GND
Pin 21 - AREF - Analog reference pin for ADC
Pin 20 - AVcc - Suppply voltage for the ADC converter. Needs to be connected to power if ADC isn't being used and to power via a low-pass filter if it is (a low pass filter is a circuit that reduces noise from the power source. This example isn't using one)
Don't know why but perhaps for this tutorial there was a reason.

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bebo
 
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Re: Why is Aref connected to Vcc on a breadboard Arduino

Post by bebo »

looking at the Arduino UNO schematic, isn't Aref connected to ground with a capacitor?

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adafruit_support_mike
 
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Re: Why is Aref connected to Vcc on a breadboard Arduino

Post by adafruit_support_mike »

You need to be careful with the Aref pin because it makes a low-resistance connection to whatever reference source is selected. If you connect Aref to 5v and select the internal 1.1v reference in software, you'll short those two voltages together, possibly damaging the chip.

The bootloader's default reference is external/5v, so connecting Aref to the 5v/VCC rail isn't an automatic disaster. It is something to be aware of though.

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bebo
 
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Re: Why is Aref connected to Vcc on a breadboard Arduino

Post by bebo »

Thanks for the clarification

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