Measure Voltage using Microcontroller

Ok, so I have done a lot of research on how to measure voltage using Microcontroller. I have read multiple articles and most of them talk about using resistor divider circuit to measure voltage. Now, say I want to measure voltage drop across a bulb rated at 12-18VDC and send this to ADC on the microcontroller. To do this I have designed the attached circuit. I was also planning on incorporate a 5.1V Zener Diode in my circuit to make sure that Va does not exceed 5V. Do you think I will run into errors using this circuit? Am I sending the right input to ADC? (I believe not!)

Any suggestions/help would be appreciated.

Thanks guys!

EDITED: Attached file

check this simple digital voltmeter project:
http://www.8051projects.net/download-d214-simple-digital-voltmeter-using-8051.html

In this project I have explained how to design proper voltage divider for your design or voltage range.

Thanks for you reply, Ajay.
Can I connect my load, in this case, a 12-18VDC bulb between Probe+ and Probe-? Please see the attached file...
Would that give me the voltage drop at my load?

EDITED:
Sorry I just noticed that I moved the text for the capacitor next to the load. Please ignore that. The load is still a bulb. Also, I understand I'd have to play with resistances a little if my input is 18V. I believe all that would change,would bethe resistances in the voltage divider circuit... everything else would be pretty much the same, right? I have no clue how you go about finding the values of capacitors.

Thanks again, Ajay.

input range is currently 0-15V DC. you can extend this to 20V to go upto 18V. There is a volt.txt file inside which tells you how to calculate voltage divider value for your design.

Yeah, I saw that. I know how to find the values for resistors, but just wanted to confirm the probes were where you apply the input voltage. Also, I worked on Multisim simulation last night and I have all connections done right. Multisim doesn't have ADC0804, so I ended up using the Generic ADC which does not have CLK IN, CLK R pins. I was curious if that was necessary. This is pretty much what it has -

If you have proteus then simulation becomes much easier. Try to install it and run the complete simulation including microcontroller code.

Did you include the proteus simulation in the zip file? If yes, what would the extension be?

I dont remember if its included it or not. see if .dsn file is there or not. that would be proteus design file.

Nope, I don't see it, Ajay. Could you include that in the zip file if you still have it.

Thanks a lot.

PS: You've a great website here. I would love to share my project here, once I am done.

Thanks for all your help!