# Working knowledge of a multimeter

#### snake doctor

Joined Jul 2, 2006
4
I'am looking for a understanding of how the meter converts it's reading to a
display for a class i'am teaching this summer.

#### Papabravo

Joined Feb 24, 2006
14,393
A digital meter reads a binary value from an Analog to Digital Converter. This binary value is converted to a string of decimal digits which are then written to the display. Is that sufficient for your purposes?

#### snake doctor

Joined Jul 2, 2006
4
Papabravo said:
A digital meter reads a binary value from an Analog to Digital Converter. This binary value is converted to a string of decimal digits which are then written to the display. Is that sufficient for your purposes?
Pababravo: thank you for this information.But how does it get converted to a string of decimal digets and what device uses the decimal conversion to activate the LCD. Could I show my class that I could use that device to actvate
other things?That would reference to the voltage.

#### Papabravo

Joined Feb 24, 2006
14,393
The device which does this conversion is a processor which is capable of executing a string of instructions. A binary number is converted to a string of decimal digits by integer division and remainder. For example if I take an eight bit binary number, which I read from an Analog to Digital Converter, and I have an operation which provides the quotient and remainder of a division operation, I can compute the decimal digit string.
Rich (BB code):
let a/b be the INTEGER quotient of a divided by b
let a%b be the remainder of a divided by b

let n be an arbitrary eight bit quantity in the range [0..255]
let 197 be such a number
We are looking for three decimal digits to display

d2 = n  / 100 and r2 = n % 100 --> d2 = 197 / 100 = 1 and r2 = 197 % 100 = 97
d1 = r2 / 10  and r1 = r2 % 10 --> d1 = 97 / 10 = 9 and r1 = 97 % 10 = 7
d0 = r1 / 1 --> d0 = 7 / 1 = 7
The digits to be displayed left to right are d2:d1:d0 where the colons indicate that the three results are to be joined together to form a three digit decimal number. Thus 1:9:7

An LCD, that displays characters, will be able to lookup the dot pattern for a given digit from just the value of the digit. There might be a constant that you have to add to serve as an offset into the display's character to dot pattern lookup table. In a graphics display you have to use the character to looup a series of dot patterns that are written to the dispaly memory one row or one column at a time.

#### snake doctor

Joined Jul 2, 2006
4
Papabravo:
Whould it possible to talk with you on the telephone about my class project.I think Iwould be able to understand and accumlate what I need to know
faster also what I need to purchase to make this a captivating project for my class.If you prefere I can send you my number If you aren,t able to send me your,s.

#### Papabravo

Joined Feb 24, 2006
14,393
I'm sorry but I do not have a telephone. I've no need for one anymore.

#### snake doctor

Joined Jul 2, 2006
4
Papabrva:

I can understand that I just have a cellphone.We'll I as guess we can make the project a winner, it will take a little longer but if you have a little patience I think it will work out just fine.First are pretty much all processars that convert the reading to a bianary number using the same Integer bianary division formua or process?Then what would I need to have that code be recieved and activate something,EX. light bulbs, an electrical shock,etc.

#### Papabravo

Joined Feb 24, 2006
14,393
I don't have a cellphone either.

Integer division is the same process on all processors. To display or print numbers or letters on a device requires that information be sent or written to the device in a certain way. There are standards in the computer and coomunications industry for the representations of characters and numbers. One of the standards is called ASCII, which is an acronym for American Standard Code for Information Interchange. IBM created a similar standard called EBCDIC which stands for Extended Binary Coded Decimal Interchange Code.

In these codes each displayable or printable character is assigned a numeric value. In a computer's memory you would see a long string of numbers. The display device or printer will convert these numbers into pixels, dots, or segments that we recognize as characters in our written language.

Due to the large number of languages on the planet, with different character sets, there is a newer standard called unicode where characters are assigned 16 bit numbers. Are there more than 65,536 symbols used in the Earth's languages? I guess we'll find out.

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

I have appended the datasheet for an Intersil ICL7106. That's an old workhorse 3 1/2 digit meter ic. It combines the a to d converter and display driver. This should give you a good explanation of the process.

Whoops, I can't get the attachment to go. Go to Intersil's website and look up the ICL7106 under data conversion.

#### rukrazy?

Joined Mar 5, 2005
21
The main principle is an analog to decimal converter. It takes a sample of the incoming voltage and samples it into time by averaging it. It is then converted though math to digital values and in turn by a BCD converter and sent to a array or matrix. The matrix is driven by a digital driver to the display to show up as a digital readout.

The sytem is more complex and the steps may not be in the order chain of events. But its a simple explanation. My classes in digital electronics is over 10 years old but the principle are still the same.

By the tone of your question you will need to do a lot more study to understand analog to digital conversion, then a small forum like this can provde time wise.

#### beenthere

Joined Apr 20, 2004
15,819
Hi,The process of analog to digital conversion is a bit different from averaging over time. Generally, a sample-and-hold amp freezes the analog waveform and presents it to a voltage comparator. The internal BCD counter (this is limited to metering a to ds) counts up or down until the comparator indicates that the voltages match. The count is the BCD equivalent of the sampled analog voltage. The BCD count is translated by logic to drive either lcd or led displays.See the section on a to d converters on this site to get more detail on the process.