Interfacing an LCD to pic16f876a for Digital Voltmeter

[paulfjujo]

hello,
Add 1or 2 normal diode as 1N4118 or other in serial with your zener
to increase voltage limit on ADC input.
4,2+0.6+0.6-> 5,4V

 

[sahu]

u can use 4.7 k & 2.2 k its give better result

+ ve volt ---^^^^---- ADC I\P 
             4.7 k    |
                      |
                      >
                      >  2.2k
                      >
                      |
                      |
                     ---
                      -

 

[jean12]

have you tested with those values??

Thanks.

 

[paulfjujo]

hello

With those values you are over 5V .. > 9,5V.
I thing the values used by jean12 3900 and 780 ohms for
30V input 5V output are correct.
Normaly a little bit less because ADC input in parralle with the 780 ohms..
The 5V Zener value could be inside the low tolerance of specification..
so adding normal rectifier diode in serial with the zener , will increase the threshol of about 0,6V per diode.

u can use 4.7 k & 2.2 k its give better result

 

[jayanth.devarayanadurga]

I already mentioned 6.5k and 1.3k. jean's value is also right but the current will be 6.4 mA. In my design current is 3.8 mA.