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Help with 7 segment LED

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snake126

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Hello everyone, I am working on a project where I would like to install one of these:
**broken link removed**

and have it display completely random things (dont even have to be numbers) How could I possible go about doing this?

Thanks
 
There are a few ways, One is to use a binary counter IC like a 4024 and connect the outputs to the segments. This will not really be random but would appear to be. Another way is to use a linear feedback shift register. A 3rd way is to use a microcontroller with a pseudo random generator routine.
 
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Which do you think would be the easiest/cheapest? I have experience soldering, but not so much making things from scratch like this.
 
I basically want to be able to flip a switch, then it comes on and is showing random and changing until i flip the switch back off.

Thanks for all your help
 
Would it be possible to just have a switch turn the display on, and have it wired up to show a character that doesnt resemble an letter or number and have it stay on that constantly? Could you direct me to a tutorial or something on how to do that since it seems to make things simple.

Thanks
 
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I won't be able to explain it well or make pretty pictures but the segment current and voltage is not known. Can assume it's 20 mA and 1.2-2.1 V.

That display is a common cathode, which makes it a bit wierd. You may want a brightness control and PWM or Pulse width modulation can easily do it. Velleman has a nice kit. You can pulse the common cathode to ground with the variable pulse width. Later you can use other methods to detect the amount of light and vary the brightness automatically.

You'll need a 5V supply and at least 1 ULN2003 IC. Each segment has to be connected to a resistor that supplies about 20 mA to the segment. So R~= (5-2.1-0.6)/20e-3 ohms. There is an extra drop in the driver.

I'm using the driver approach in case you want to convert to a microcontroller.

Now, you can use two rotary hex switches to control 4 lines to get 16 possibilites and I think 2 switches will connect to 8 line. 7 segments and one decimal point. Sometimes there is two.

Later when you change to a microcontroller, set your hex switches (probably to zero) or socket them and pull them out. Some switches that can be used are: Electronic Components Distributor | DigiKey Corp. | US Home Page, use "dip hex switch" as a search term.

These are available comlementary or non-complementary.

You set up a logic high on one side of the switch. Probably a 470 ohm resistor to +5 and feed it to the switch. This will set a logic 1 on theULN2003 driver and the other side (cathode) would be grounded using PWM.

It's a place to start, but you probably didn't understand a word I said.

https://www.electro-tech-online.com/custompdfs/2011/04/illustrated_assembly_manual_k8004_rev3.pdf is being mean and won't operate off of 5 volts. The display can be changed to operate off of a 12 V supply or you can find other ways of generating the PWM you need for brightness.

If you went with "common anode" supplies, then you could supply a variable voltage at the anode.

Look up the data sheets on the uln200x parts, the PWM gizmo and other LED display supplier such as DIGIKEY

Your project is simple and I've made it more complex.
1. pattern is easy to change
2. added a brightness control
3. Future - link brightness to ambient light
4. Future - Can use microcontroller to generate random numbers.
5. Future - microcontroller replaces PWM gizmo

I did not allow a manual/auto mode for future that uses the same switches. I didn't do the design or select the parts.

Even simpler is a shorting jumper for each segment. The hex switches make it easier. You could easy select pattern A6 if you liked it.
The patters would be 00 through FF hex which is 256 different patterns if you include nothing as a pattern.

Read and ask questions.
 
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