Please criticise my schematic

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#1
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Greetings,

I am working on my first schematic, but before I get very far with it I would like to know if I have any bad habits, practices, etc.

Please review the attached schematic and point out any bad habits you may find.

Cheers

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Are you using net names as labels for the interconnections? I see the +5v is directly connected to vcc which would not normally happen unless it has been aliased. Also I'd put the labels for the power horizontally just so i don't have to keep twisting my head. Preference only!

John.

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AVCC must be connected, easiest is to VCC. I would add a cap (10nF) from reset to GND.

/Martin.

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AVCC MAY be connected, NOT! must!

Connect it if you intend to use it as a reference input for ADC. AVCC is connected to the ADCs reference input through a passive switch and is selected through the ADMUX register.

Also remember that care must be taken if pin AREFF is connected to an external source at the same time as you intend to use AVCC as reference since then you will shorten AREFF and AVCC with damage to your device as an possible result.

However, it may be advisable to connect a small capp between AVCC and ground. Ive seen that from time to time, however, as long it is not selected internally you should have no worries aboute it.

Regards
Vidar (Z)

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"The fool wonders, the wise man asks"

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Quote:
AVCC MAY be connected, NOT! must!

AREF MAY be connected, AVCC MUST.
According to the datasheet, ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±0.3V from VCC.
AVCC is also used to source the I/O-Pins of PORTC.

/Martin.

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Yes, the datasheet clearly states AVCC must be connected:

Datasheet wrote:
AVCC is the supply voltage pin for the A/D Converter, PC3..0, and ADC7..6. It should be
externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be
connected to VCC through a low-pass filter. Note that PC6..4 use digital supply voltage,
VCC.

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Add bypass caps at pins 4,6 on AVR VCC pins. Perhaps one 22 ufd tantalum and 0.1 ufd ceramics on each pin. Better to have more than less.

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Seperate 100 nF decoupling capacitors für both Vcc and Avcc is a good idea, but its enough to have one electrolytic capacitor for both.

The readability of the shematics is also not good. The resolution just seems to be a bad choice.

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Arrrgh, yes, offcourse. Sorry for the misleading.
AVCC must, AVREF may, but never when intending to use AVCC as source.

Regards
Vidar (Z)

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"The fool wonders, the wise man asks"

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Get it, AVCC must be connected, and AREF may be connected.

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I always tend to use a push button switch from the Reset pin to GND with a cap to GND as well. This way you can reset your uC if needed. Of course you may need debouncing for this. (Search Ganssle debouncing on this forum for more info on debouncing)

I also like to bring out all my useful uC port pins out to headers so that I can use them in the future if needed. (just like you have brought out the ADC pins on the jumper).

One more thing I learned here on the forum is to add test points (single pin headers) to all critical nodes in the circuit (like for example the RESET pin, used ports,etc.). This will help you immensely in troubleshooting if needed later.

Also is the RESET net on the jumper same as the uC reset net?

My two cents.