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Arduino Analog pin pullup and pulldown

hello,
please see the attached image of my circuit, it has atmega328pu MCU. i am unable to understand few connection, PC1 and PC4. PC1 is connected to ground via 1k resistor and PC4 is connected to vcc and 1K resistor. PC0 to current sensor output, PC6 to usb, PC2 & PC3 to swictch, PC5 not connected. I want to know why PC1 and PC4 are connected to ground and vcc.118275
 

Pommie

Well-Known Member
Most Helpful Member
Check the specs but some Arduinos require some pins to be tied high/low in order to tell them what to do at powerup. The configuration above probably tells it to go to the boot loader which is not something you'd want on a finished device.

Mike.
Edit, where is that schematic from? 1k resistors across the supply seems like a very silly idea.
 
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the circuit is part of sim800 and atmega328pu on single board. PC is pull down then why i am getting 1023 in the serial monitor from PC1, so i checked with a multimeter and found that PC1 is short with VCC. I am pretty confused on this. Actually, i am trying to use PC1 pin for a sensor.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Well it looks like the partial circuit you posted is nothing like reality, so we can't really make any sensible suggestions.

You need to post the FULL circuit, as it's actually constructed - not a theoretical version.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
That just the full version of the partial one you posted (or at least 'fuller'), you've already pointed out that PC1 is connected to Vcc, which it doesn't show on that PDF, so it might have no bearing on what you actually have.

However, it's rather bizarre having 1K pull downs? (VERY wasteful of current), even more so when they appear to be connected from Vcc to ground. There's a third one on PB4, this time with a switch to Vcc (if the circuit can be believed), again far too low a value for such a use.

I've just noticed what PC1 is doing, it connects to J1, which is a switched socket - and connects PC1 to Vcc, until you plug something in the socket.

There are plenty of free I/O pins, why not use one of those?.
 
That just the full version of the partial one you posted (or at least 'fuller'), you've already pointed out that PC1 is connected to Vcc, which it doesn't show on that PDF, so it might have no bearing on what you actually have.

However, it's rather bizarre having 1K pull downs? (VERY wasteful of current), even more so when they appear to be connected from Vcc to ground. There's a third one on PB4, this time with a switch to Vcc (if the circuit can be believed), again far too low a value for such a use.

I've just noticed what PC1 is doing, it connects to J1, which is a switched socket - and connects PC1 to Vcc, until you plug something in the socket.

There are plenty of free I/O pins, why not use one of those?.
thanks for input its very helpful in solving my problem
 

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