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8 7-segment displays in a row, control through two wires by an IC

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cavemen

Sun May 09 2010, 12:26AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

In both circuits, the7 segmant number display array is controlled by two wires.
How do they do it?
wouldn't it just all light up?

I understand that that IC pulses the input to every segment, but how?
None of the old radioham books tell me that?

Is it a special display with the encoder already in it?
Or is it some duty-cycle trick I don't get?

This will be incorporated in to my project if you tell me.
Thank you.

V.T.

Bjørn

Sun May 09 2010, 12:47AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

There are 16 wires, they are just bundled up to make the diagram tidy, alternatively people do that when they are lazy. Just have a look at the datasheet of the driver chip. 8 select lines choose the digit that will be displayed and 8 databits is used to light up the required segments of that digit. So only one digit lights up at a time. When it is done fast enough it looks like they all are lit up at the same time.

If you want to use 2-3 wires you can use 74HC595 chips or other serial in parallel out chips and do the same thing manually without the driver chip.

hboy007

Sun May 09 2010, 03:07PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374

Bjorn is right about the diagram, these are bus lines that bundle the different signals to make the schematic look better.

I once buit a 4 digit display with a 2-wire interface using four CD4094 shift registers, this is really simple and you don't need an active driver IC that cycles through the display segments, it's all static once data is filled in. If you do not like the subtle flashing during filling, you might want to check out 74HC573, that's an octal tri-statable latch that allows you to buffer the bits for one digit.

Both ICs are cheap standard cmos devices and they only matter when it comes to space consumption.

Renesis

Sun May 09 2010, 06:33PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

BjÃ¸rn wrote ...

8 select lines choose the digit that will be displayed and 8 databits is used to light up the required segments of that digit. So only one digit lights up at a time. When it is done fast enough it looks like they all are lit up at the same time.

If your goal is to use as few lines as possible while still using old fashioned multiplexing as BjÃ¸rn just described, you could use a Johnson-counter to select which digit to display an thus replace the 8 digit selection lines with one "count-up" and one reset line.

By using a 7-segment decoder/driver at the display you might also replace the 8 segment lines with 4 data lines, and send the wanted digit as a binary byte. But this would only work if you were going to display decimal digits (0-9), and nothing else.

cavemen

Mon May 10 2010, 04:31PM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Thank you for explaining.

Do they have integrated frequency generator ICs out on the market?
I am wondering if there is an IC that can take a binary input of the frequency we want it to produce and put out that frequency.

I know that there are many integrated sensors on the market that put out a binary code.

Thank you.

,%20PLLs,%20Frequency%20Synthesizers/800-1261-1- datasheetz.html

i found one myself

I am thinking of building a system that uses the pic controler, integrated frequency generator chip and a 7 segment display to find the self-frequency of a tesla resonator and drive tesla coil at that frequency, while displaying the resonance.

What kind of techniques do I use to match outputs of one IC to inputs of another? Do I rely solely on their datasheets?
SImulators?
Breadboard and scope?

We get small value capacitors in circuits between ICs once in a while.
For noise filtration, etc.
How are values of those capacitors determined?

[Edit: Double post]

Steve Conner

Mon May 10 2010, 04:52PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

cavemen wrote ...

I am wondering if there is an IC that can take a binary input of the frequency we want it to produce and put out that frequency.

Yes, they are called DDS. (Direct Digital Synthesizer)

The AD9850 from Analog Devices is a popular one that I've used. It can generate any frequency from 0 to 40MHz in 0.02Hz steps.

If the frequency is not too high, you can make your own with a microcontroller.

Bjørn

Mon May 10 2010, 05:20PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

You read the datasheets and think, then you make a prototype using experience from earlier projects. Then you test it and find out what needs to be improved. The values of certain components can be found in datasheets or or by experience. In some cases bypass capacitors are not needed but they are put in just in case since it is little extra work that can save you a week of trouble.

See here for frequency synthesis with a microcontroller

All common microcontrollers have special hardware to make frequencies with a period that is a multiple of the main clock period. So if that gives the resolution you need it would be a lot simpler and cheaper.

cavemen

Tue May 11 2010, 02:05AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Thank you very much.
So what freqency range do tesla coils run in?

Would a PIC controller be big enough for the tesla coil application I am trying to do?

cavemen

Tue May 11 2010, 02:13AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Thank you very much.
So what freqency range do tesla coils run in?

Would a PIC controller be big enough for the tesla coil application I am trying to do?

Killa-X

Tue May 11 2010, 04:26AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

do you have a specific model in mind? I'm a AVR fan, and they make 25mhz crystals for them...Technically speaking, it should mean you can do 1hz to ~25mhz reading almost. As for the range, all depends on size. I've made / seen coils at 80khz, and seen them at 1mhz+

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