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digital voltmeter

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danos

New Member
hello there...
I could use your help...
I need to make a voltmeter that measures max of 24 volts. For output to have 7-segment display.
If you have any ideas how to get this started or even a complete disign (same or similar specs) i really could appriciate it.

Thank you.
 

danos

New Member
thnx

thnx for the reply...
i ve seen the datasheets but there is not much for me there :shock:
i was wondering if you could be a bit more specific and explain the principle about how this is going to work...

Thank you
 

Exo

Active Member
If you want to display a analog voltage on a display then you're going to need a Analog to digital (A/D) converter... A device that changes a analog voltage into a digital value for you to work with...

There are diffirent kinds of A/D's. Some offer a serial interface for a µController, others offer a parallel output and others are capable of directly driving a display...

The link i gave you are such devices... There should be scematics in the datasheets...
 

danos

New Member
I know that, but...

thanks for your reply for one more time....
but i already know that do you mean.
the problem that i have is that i cannot get an analogue singal at the first place, and i was wondering if you had any kind of idea to do that. an initial voltmeter design for instance!!

Anyway, thanks very much for your time!!xxx
 

Exo

Active Member
i'm getting confused here...

You say you want to make a digital voltmeter; so i assume you want to measure a voltage....
The voltage you want to measure is the analog signal...
 

danos

New Member
More details

Well, lets ake this clear...
i need a battery energy mesurement system!!
I simple words... a voltmeter (digital is preffered), which is gonna be able to measure the battery (24V max) at any time and display this raeding in a 7 segment display.
i dont care whether the initial design is gonna be analog or whatever, the only thing that i need is a design to start with...
afterwards i can use a A/D converter to apply it to the display.

i hope this is clearer for you!! sorry for the misunderstanding

Thnaks
 

danos

New Member
OK... thanks

ok you were right!!

sorry for the misunderstanding, but i didnt had a proper look at the specs!!

anyway, talk to you later
 

Exo

Active Member
Add a voltage divider to get your input within scale

So for example, if you set your reference voltage to 100mV
and you divide your input by 1000 then the display will show 24.0 at 24V and 100.0 at 100V

Dividing is done with (precision) resistors .
For example if you add 2 resistors in series between Vin+ and Vin- with values 1K and 99K then in between you'll have a voltage divided by 100
 

danos

New Member
you see, i'm troubled about what is writen in page 4 of the chip you mentioned, where it says as a note that "Input voltages may exceed the supply voltages, prodived the input current is limited to -/+ 100uA".

i want to measure voltage and current from 4 car batteries connected in series, summing to 48V, and i'll probably burn this chip.
do you know any way that i can reduce the current (which i believe it will be around 6~10A) to the current of the chip requires (some uA)?

thanks for your help and speedy response!
 

Exo

Active Member
First of all - like i said in my previous post. You need to divide the voltage you measure with resistors. If you give the chip a reference of 1V and you divide your voltage by 100. The meter will read 48.0 when your voltage is 48V... Because of the division the chip actually only gets 0.48V
wich is safely below the supply voltage of max 15V

Secondly the input current of the chip and the current the to the device that is connected to the batteries have nothing to do with each other. The input current of the chip is influenced by the input voltage and the chips input resistance... It has nothing to do with the load you are driving.
 

23401040

New Member
A PIC16F84 base Volt Meter?

Hi, this one is for Exo, :)

I've posted a reply on the topic by sofia, on how to work on a digital clock, I have 4 weeks for a class project, and I'm going to hand in several Ideas to my lecturer, the first are the digital clock, second maybe a combination lock (with no reality use at all, just accept and deny true/false codes), and I'm interested to know how to make a PIC16F84 base voltmeter, can it be more complicated than the other two?will implementing the program be difficult, I only know about assembly so far, and that isn't much too, just some simple LED programs, you know... the basic input output for PIC16F84 :(

Or maybe you can give another Idea, I would appreciate it a lot, but I would appreciate any help at all actually :lol:

Thanks a lot
 

Exo

Active Member
A digital voltmeter with a pic isn't that difficult. Find yourself a nice A/D converter. You can use all sorts of A/D's parallel outputs, serial outputs...

Parallel A/D's are easyer to program, but require more pins, serial versiond will do with a pin or 2 but require code to clock the serial data in.

Once you got your data displaying it on a 7-Segment or even a HD7780 LCD is no problem

Microchip itself has quite a range of A/D's and also example pic code on how to interface them
www.microchip.com

Other manufacturers like Analogdevices and national offer great devices too
 

23401040

New Member
Where to start?

Hmm, thanks a lot for the quick reply, I'm still online right now.

er.. if I choose a parallel A/D for my voltmeter, what issue will I encounter?

I have no Idea on how to design the circuit from scratch, will I find it on the microchip web page?

displaying a digital data on a seven segment will be simpler than doing it on a HDD7780 right?

btw do u mind if I contact u using ICQ? I know this is quite unnatural but in Indonesia the online costs for dialups will cost a fortune...

so I think if I leave can msgs on ICQ for u about this... it would be very much helpful...
:)

thanks a lot
 

Exo

Active Member
Re: Where to start?

23401040 said:
Hmm, thanks a lot for the quick reply, I'm still online right now.

er.. if I choose a parallel A/D for my voltmeter, what issue will I encounter?

I have no Idea on how to design the circuit from scratch, will I find it on the microchip web page?
There may be some application notes about such a circuit. Also try searching the net for A/D converters & pic circuits



23401040 said:
displaying a digital data on a seven segment will be simpler than doing it on a HDD7780 right?
Once you get the hang of it i think an lcd is easyer. Both 7-segments and a lcd require lots's of pic pins if connected parallel. So you'll probabely will use some way of conversion to drive tha 7-segment/lcd serially (trough a shift register for example). If so, the 7-segment will require constant updating (otherwise you'll see it flicker) while the lcd only requires few extra lines of code.

A good site 'bout 44780LCD's
http://home.iae.nl/users/pouweha/lcd/lcd.shtml

A little example of how to drive a lcd using only 3 pic pins i once posted here
http://www.electro-tech-online.com/download.php?id=804

23401040 said:
btw do u mind if I contact u using ICQ? I know this is quite unnatural but in Indonesia the online costs for dialups will cost a fortune...

so I think if I leave can msgs on ICQ for u about this... it would be very much helpful...
:)
My ICQ is running on my server. And i don't check it regularly so you'll have to be very lucky to catch me on icq.
 

23401040

New Member
I've searched the net on a/d converters, arent they ICs with those capability??

I've just found out that an a/d converter is a circuit... :shock:

I have a problem with combining one circuit to another because of the low knowledge on analog electronics :(

What exactly is a parallel A/D converter?my recent searches havent found a parallel output a/d yet, but I'm going to keep searching...

I'm going to keep updating my posts every day, so if any of the fellow community have some time, please allocate some to view and give comment or answers on my messages, I really wanted to learn and build it until it finishes, thank you, appreciate it. :)
 

Exo

Active Member
A A/D is a circuit that 'translates' an analog voltage into a digital value, a number. It has a positive and a negative reference. For example GND as negative ref. +5V as positive ref. It will output the lowest number (0) when the analog voltage is equal to the negative reference. And output the highest number (dependent on the resolution) when the input is equal to the positive reference.

The A/D has a resolution in bits. This is the precision of the conversion. For example if the converter has a resolution of 8-Bits then the value returned will be in the range of 0 - 255 (255 is the biggest number 8 bits can store). If you want to measure a voltage of 255 Volts with such an A/D you'll get a reading in single volts (1V..2V..3V). The resolution will be too small to go furter (i.e. it can't return 1.5)...


Parallel output or serial output defines the means of communication of the output to another device (the µController for example). Parallel just means that every bit uses a line. So for the 8 Bit A/D in the above example 8 output lines to the PIC are used. This is the simplest way, but also requires the most lines.

Serial output usually only uses a line or 2. because the bits are send one afther another. Saving lines on your PIC this method requires more software to receive all the single bits and assemble them into a single number again.

Examples of popular serial connections are I²C bus and SPI
 

23401040

New Member
Rejected...

DEar Exo...

the digital voltmeter idea for my class project was already taken T_T , so I have to figure out something else, sorry to have bother you with my questions... :cry:

the project that is accepted is a combination lock project, I'm planning to use a combination of pressed keypad to light a LED, but my lecturer says I better concentrate n how to use the EEPROM abilities of the PIC16F84, since it was the microchip I was assigned at.

Will it be okay If I ask you to help me on this one, it is already accepted though, so I'll have to work on it.

I will post a new topic some time tommorow.

Thank you.
 
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