Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

current limitations of adc analog input module of p16f877

Status
Not open for further replies.

ronrayzap

Newbie level 2
Joined
Jan 26, 2006
Messages
2
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,303
i just wana ask if there are any limitations in electric current being inputted in the adc module of the pic16f877?

i am presently working on a project using the adc module and i have configured it as a 4 7-segment digit voltmeter in the mean time to test it. when i input 5v from the pic supply itself using a potentiometer to vary the analog input, the adc reacts well. the problem is when i input voltage from a dc voltage supply through a voltage divider, my circuit doesnt read the input and just displays the digit "8" in the least significant spot.

im just wondering why this happens and if the current in the voltage source has an effect because the current of the dc supply is significantly higher.

has anyone else experienced this? thanx for all the help in advance.
 

philba

Full Member level 2
Joined
Jan 26, 2006
Messages
132
Helped
13
Reputation
26
Reaction score
1
Trophy points
1,298
Activity points
3,102
pay attention to the impedence of the input - this is described in the datasheet. IIRC, it must be below 10K.

also, make sure you have a common ground.
 

vsgiri

Member level 5
Joined
Feb 24, 2006
Messages
86
Helped
10
Reputation
20
Reaction score
3
Trophy points
1,288
Activity points
2,140
When you have an external supply, as Philba suggested, make a common ground. Then protect the input of ADC using a series resistance (1k) and a zener(equivalent to supply voltage) to gnd. Also put a .1uF capacitor to gnd to check stray noise.
If your voltage supply can supply high current that is good enough. You are actually choking it with voltage divider and series protection resistor. Is the ADC result register giving random values or is it stuck at some value?
 

ronrayzap

Newbie level 2
Joined
Jan 26, 2006
Messages
2
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,303
thanx for the replies, im gonna try those and update again..

vsgiri - i havent checked the adc result register itself but the output on the 7-segment digits only displays an 8 in the least significant digit.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top