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[SOLVED] Problem with arduino circuit voltage

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roboyoyo

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arduino circuit .

How I can determine the down and up limit voltage ?
 
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Re: arduino circuit .

connect it to a transistor and use a pull down network :)
 

Are you sure that your avr pins are set up as outputs?
I don't see a way that this can happen unless you pull too much current from the avr and you don't do that, unless you have damaged any of your pins before.
You can try with 3 leds connected to the 3 outputs of the avr, each with a resistor about 300 ohm, anode to the vcc supply and cathode to the avr to see if the avr can sink the current.
The led will turn on with 0 and turn off with 1

Alex
 

you are mentioning about the loading problem.do one thing build a comparator circuit using op amp whose saturation values at 0V and 5V.one thing you should always remember dont use digital circuit element to drive high current values always try to use drivers , it will be a good practice.you can also use a transistor as a switch for your circuit.
 

drivers are just circuit which help to connect between two different impedance circuit by neglecting loading problem.for simplicity if i m using a voltage divider using res r1 and r2( connected in series) and i want to draw the voltage across the res r2 to another resistor r3, if i connect this r3 parallel to r2 then the equ res will be (r=r2r3/(r2+r3)).so the voltage will be reduced.if i connect a driver circuit in between this r3 get exactly same voltage that indented to give.i think you use op amp circuitry(search for comparators) which have higher saturation at 5v(logic high) and low saturation at 0v (logic low).

---------- Post added at 10:33 ---------- Previous post was at 10:30 ----------

you can also connect a diode in series (this will be the simplest solution ) and it will reduce the voltage 0.7 v so you will get 4.3v and 0.5v as logic high and low respectively.
 

Can you please specify where exactly you have a problem, is it the avr, the 74LS156 or the 74HC86.
You only need a driver in the final stage (74HC86) to be able to drive the output stage with current that is enough to drive that stage.
Also where are these resistors you talk about, are they the ones connected to 74LS156 output or do you have other resistors in the avr outputs.

Alex
 
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