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How to represent analog signals into voltages?

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lee_080487

New Member
Can somebody help me with my project? I'm looking for a circuit that works as a digital weight meter since I don't know how to represent weight/mass into voltages. Our teacher requires us not to use ADC ICs thus we need to use the other way around like OP AMPs and other logic circuits for analog to digital conversion.

The deadline will be on this coming March 2008 thus I badly needed your assistance. I'm still open for some changes if I can't make this digital weight/mass meter project. Your suggestions will be much appreciated.

Thank you. :)
 

dknguyen

Well-Known Member
Most Helpful Member
How does your teacher expect you to turn an "analog signal to a digital signal "without an "analog-to-digital converter"? Maybe a few more details and we'll point you in the appropriate direction.

I guess you have to GOogle ADC circuits then and do it like like that? For something like weight? An slow accurate ADC like the kind where a capacitor charges and discharges and the time measured is used will do (except I can't remember what it's called!)
 
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Roff

Well-Known Member
dknguyen said:
How does your teacher expect you to turn an "analog signal to a digital signal "without an "analog-to-digital converter"? Maybe a few more details and we'll point you in the appropriate direction.

I guess you have to GOogle ADC circuits then and do it like like that? For something like weight? An slow accurate ADC like the kind where a capacitor charges and discharges and the time measured is used will do (except I can't remember what it's called!)
I think the key is
Our teacher requires us not to use ADC ICs
.
 

Leftyretro

New Member
lee_080487 said:
Can somebody help me with my project? I'm looking for a circuit that works as a digital weight meter since I don't know how to represent weight/mass into voltages. Our teacher requires us not to use ADC ICs thus we need to use the other way around like OP AMPs and other logic circuits for analog to digital conversion.

The deadline will be on this coming March 2008 thus I badly needed your assistance. I'm still open for some changes if I can't make this digital weight/mass meter project. Your suggestions will be much appreciated.

Thank you. :)

Well study how strain gauges work first.

https://www.sensorland.com/HowPage002.html

This will result in a low DC voltage that will represent the weight of the object. This is usually amplified and adjusted for calibration with an op-amp circuit. After that you will have to figure out how to convert a analog DC voltage into a digital display without using a A/D :eek:

Lefty
 

lee_080487

New Member
dknguyen said:
How does your teacher expect you to turn an "analog signal to a digital signal "without an "analog-to-digital converter"? Maybe a few more details and we'll point you in the appropriate direction.

What I mean is we do really need an ADC circuit but we are not supposed to use ADC IC itself. My problems are:
1. I dont know how to design an ADC circuit.
2. I dont know how to represent weight/mass into voltages.

Actually, I have found an ADC schematic on the net **broken link removed** Please help me if this can be alright.But still my problem is how to have my input voltage to OP AMPS if I can't represent weight into a voltage. Anyway, If you have some ADC project easier than this, please help me with the designs. Should you have any suggestions, it will be much appreciated.. Thank you!
 
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Super_voip

New Member
There are methods using a single port on a microcontroller that use a resistor and capacitor to read voltage levels. The voltage levels usually need to reasonably large, so amplifiers will still be needed. The advatntage of this method is that it allows you to connect the display to the micro as well.
 

bobledoux

Member
Simple ADC

Look at the Parallax Basic Stamp manual "What is a Microcontroller?" They discuss the capacitor/resistor method. It involves charging a capacitor. The time it takes for a resistor to discharge the cap, thus changing states on the Microcontroller pin, is a function of the resistance. This is their method of providing an ADC on a chip that lacks it.
 

lee_080487

New Member
bobledoux said:
Look at the Parallax Basic Stamp manual "What is a Microcontroller?"

Where can I have this "Parallax Basic Stamp manual" because I can't find a more comprehensive one on the net. I'm so sorry, am so new about this ADC stuff. Our teacher only taught us the theory but designing complicated circuits such as this with myself alone, is most likely a trouble.
Can you help me find some ADC projects which are easier to understand. It will be better if there is already a schematic. Just for me, a beginner's project. hehehe. Thank you guys! :D
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Get a PIC 16F88, consult my tutorials and program it to read the analogue voltage and drive the display. File the numbers off of the chip, and tell the teacher it's an analogue display chip (which it is once you've programmed it).
 

bobledoux

Member
lee_080487 said:
Where can I have this "Parallax Basic Stamp manual" because I can't find a more comprehensive one on the net. I'm so sorry, am so new about this ADC stuff. Our teacher only taught us the theory but designing complicated circuits such as this with myself alone, is most likely a trouble.
Can you help me find some ADC projects which are easier to understand. It will be better if there is already a schematic. Just for me, a beginner's project. hehehe. Thank you guys! :D

Try here:

https://www.electro-tech-online.com/custompdfs/2008/01/BAADv13.pdf
 

Roff

Well-Known Member
If this were my problem, and I didn't want to use a microcontroller, I'd probably make a 4-bit tracking A/D. You can one with an up/down counter (CD4516), a comparator (LM393), and a binary-weighted resistor DAC. You have to add a little logic to make it clip when overdriven, instead of folding over, which it will do otherwise.
 

lee_080487

New Member
Roff said:
If this were my problem, and I didn't want to use a microcontroller, I'd probably make a 4-bit tracking A/D. You can one with an up/down counter (CD4516), a comparator (LM393), and a binary-weighted resistor DAC. You have to add a little logic to make it clip when overdriven, instead of folding over, which it will do otherwise.

Mr. Roff,

Yes, I dont want to use a microcontroller because it's a bit complicated. By the way, what do you mean by a 4-bit tracking A/D? Can it solve my problem, on how to represent weight into voltages as my input to my ADC?

Lee
 

Roff

Well-Known Member
lee_080487 said:
Mr. Roff,

Yes, I dont want to use a microcontroller because it's a bit complicated. By the way, what do you mean by a 4-bit tracking A/D? Can it solve my problem, on how to represent weight into voltages as my input to my ADC?

Lee
No, it is an ADC. A/D is another abbreviation for Analog to Digital Converter. You still have to come up with a way to convert voltage to weight. Strain guages are the most common method, but using one may be beyond your capabilities.
 

lee_080487

New Member
Mr Roff,

I have found I guess a simple capacitance or inductance meter on the net, http://braincambre500.freeservers.com/indcap.htm. Can you please take a look at this site if this is okay for ADC project? As you see, the output shown on the diagram is connected to a DVM/VOM so the output is in terms of voltage right? Now, is it the place where I should connect the ADC circuit and have the output in "numbers"? For example, the display will show "1000pF".
 

Roff

Well-Known Member
lee_080487 said:
Mr Roff,

I have found I guess a simple capacitance or inductance meter on the net, http://braincambre500.freeservers.com/indcap.htm. Can you please take a look at this site if this is okay for ADC project? As you see, the output shown on the diagram is connected to a DVM/VOM so the output is in terms of voltage right? Now, is it the place where I should connect the ADC circuit and have the output in "numbers"? For example, the display will show "1000pF".
You originally said you have to display weight digitally. Are you now saying you are allowed to convert any analog parameter to digital?
 

lee_080487

New Member
Roff said:
Are you now saying you are allowed to convert any analog parameter to digital?

Mr Roff,

Yes, that is what our project is all about. It is our choice to choose any analog signal then convert it into digital. I find the weight meter as a bit complicated one thus I changed my mind and want to try this capacitance meter instead. Did you take a look on the site I've given you for the schematic Mr Roff? Is it okay for this kind of project? I'm planning to buy ASAP the parts list but I doubt if this will work. Please help me. :confused:

Lee
 

Roff

Well-Known Member
I get the distinct impression that your instructor expects you to design something, and you hope to find some circuits you can stick together. :confused:
 

lee_080487

New Member
Roff said:
I get the distinct impression that your instructor expects you to design something, and you hope to find some circuits you can stick together. :confused:

I really want to design my project with my own but I guess it's beyond my capabilities that is why I'm searching for any ADC project on the net but somehow I would like also to understand it if I can find one. Anyway, thank you for your replies. Tc! :)
 
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