# Multiple 7 segments

Discussion in 'The Projects Forum' started by slidingman, Nov 30, 2008.

1. ### slidingman Thread Starter New Member

Nov 30, 2008
3
0
Hi,

I was wondering which chips (and I would appreciate circuit diagrams too ) would be ideal (no microcontrollers please) to use several 7 segments together to display one number. I require control for up to 5 segments showing something like this 100.00. Yes, I do require a decimal place.

I only require 3 significant digits, so I assume that having 5 segments to show 0 to 100 with decimals woud be easier if I assigned each segment to a power of 10 rather than switching places as I did my calculations. Ie, our minimum value would be 0.01 (though that is only 1 sig fig, it is an unrealistic value for the applications I will be using it for) and largest would be 100. .

2. ### mik3 Senior Member

Feb 4, 2008
4,846
69
Make a search in google for 'seven segment led drivers', you will find many.

3. ### slidingman Thread Starter New Member

Nov 30, 2008
3
0
Most of these appear prebuilt or something wiht the LEDs on them. Are there alot of well known easy to find ones in hardware stores? I remember using 74LSxxxx chips in my ICE class and multiplexors to use the seven segment but that was qutie a while ago.

Also, hate to hijack my own thread, but how does the ADC change an analog signal into digital? Specifically, what data does the ADC look at? The voltage? frequency?

I am asking because I am dealing with a circuit that gives measurements based on the amount of voltage (using thermistors ) coming through. I need to somehow turn the voltage into a digital signal.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,808
294
Here is the first of several chapters in out Ebook that explain A to D conversion - http://www.allaboutcircuits.com/vol_4/chpt_13/4.html.

You can get the whole thing in one package as a panel meter. It contains the A to D converter and display. Digi-Key has one, part #227-1060 for \$22.60. It will display 0 - 200 millivolts, so you can use it directly with the thermistor voltage.

5. ### mik3 Senior Member

Feb 4, 2008
4,846
69
There are ready chips which take an analog input and give you a digital output according to the magnitude of the voltage of the input signal.

Here are some available in the market:

Then, depending on what kind of display you want to use, you will use the proper circuitry which takes this digital output from the ADC and drives the display.
Its better to do this with a microcontroller. Many microcontrollers have built-in ADCs, so you can use only a microcontroller to make the analog to digital conversion and drive the display by itself.

6. ### slidingman Thread Starter New Member

Nov 30, 2008
3
0
Microcontrollers are banned from this project.

Furthermore, I would like to convert the AC signal which will represent a percentage, into a digital signal (0.01V per Degree celsius).

If I use ADC, I would assume I'd need to find a way to scale my voltage to the ADC's conversion factor so that my maximum voltage going into the ADC will only trigger the ADC giving a digital signal of 100?

7. ### beenthere Retired Moderator

Apr 20, 2004
15,808
294
Using a stand-alone ADC is a challenge. Most have binary outputs, which require conversion to a decimal value. For the resolution you require, the only ones available are 16 bit, giving a resolution of 1 in 32,768. 15 bit would be "ideal", with a resolution of 16,384, but the devices jump from 14 bit to 16.

One could do a conversion from binary to decimal in logic alone, but it needs a register to hold the conversion, a clock source to count that value down to zero, and another set of counters to hold the BCD count. Plus latches and display drivers.

Another way out is to obtain a digital panel meter with the resolution built in. A C-Ton CDPM70x meter has 4 1/2 digits - http://www.ctonindustries.com/cton_DK710.asp. They are available from Digi-Key for \$49.95.

Another reading of your project suggests that you only need to know if the voltage is exactly 100 (100 C? - that is not explicitly explained). In that case, all you need is a comparator that will change state at that level and signal the preset level has been reached. If that is the case, the temperature display down to 100th of a degree C would seem to be unnecessary.