I need help with digital electronics :)

[bluehand]

Hi there!, I want to make this project, but i'm noob in electronics , and i'm studying other area. (something with mechanics )

A three digit seven segment display, in which is shown a number entered by a numeric keyboard. It should can be reseted.

I've investigated it and at this moment I think it maybe will be something like this:

- Keyboard: with 12 buttons, 10 digits + reset and lamp test
- Decimal to binary converter: To pass from entered digit to a 4-bit word.
- One flip flop (I guess those is a memory), with a FIFO stack, in which the last entered digit "shifts" the last one, like in calculators.
- Three 4-bit to sevent segment display drivers.
- Three sevent segment displays (one digit each).

Keyboard => A/D converter => Flip Flop FIFO => Drivers => Display

This is a graphical representation of my idea:

**broken link removed**

I've developed the drivers -> display stage with Philips 4511 ICs (HEF4511BP) and KINGBRIGHT SC56-11HDB seven segment leds (common anode?) with a 150R Resistor in each line, I've seen there's not enought contrast in leds.

I tried to make the shift stage with 74ls164 ICs, but it was a great downfall! .

I hope you could help me in this project.

greetings to all!

(sorry for my Pre-historyc english, i hope in the future it will be better!)

 

[Someone Electro]

Shifting it can get REALY complicated whith logic chips and gates.

I sugest using an PIC micocontroler.And you can do it all whith one single chip whith almost no external components.These are cheap miniature computers in a single chip.They cost from $1 to $20 (Depends on the fetrures it has)You can get them for free trough microchips samples service.

You can write an program for them.

An 28 pin one shod do.

Unles you are not alowed to use an microcontroler.

 

[bluehand]

i'm allowed to use everything! 'cause there's not restrictions in this project.

What about programming a pic? do i need special hardware?

I heard somewhere pic programmers machines are very expensive!. Is this the only practical way to make my project?

thanks a lot!

 

[Someone Electro]

No you can make your own programer for a few dolars.Simple ones have about 5 to 20 components(Traistors,resisotrs,caps...).

As for writing the program,its not all that hard especialy if you programed before.

 

[electronist]

No, you do not require expensice hardware or software. Infact the design and software is easily available on the net. A similar code for interfacing keyboard to a PIC is also available freely. Ive built a door lock security system using the PIC 16F84A and it is working fantastic. You can google OSHON PIC programmers and simulators for free downloads

 

[bluehand]

Wow, i had afraid of pic, microcontrollers, etc, but... If do I try it?
well, i hope you will bring me your assistance, you make the things easier to understand.

I found in a local shop the pic 16F84A, now i need the programer... and the program :roll: ...

 

[Someone Electro]

An PIC16F84A is an old chip that isent even in production anymore.

But you can make an programer for it out of a a cuple resistors.

And you may need more I/O pins!

The abosult minimum if I/O pins is about 14 for you design.

 

[electronist]

The PIC 16F84 may not be in production but there ate still millions of this chip available in the market. Regarding the software and hardware design try this link www.oshonsoft.com. This is an easy chip to master with only 35 instructions

 

[Nigel Goodwin]

The PIC 16F84 may not be in production but there ate still millions of this chip available in the market.

Yes, but it's replacement the 16F628 is better and cheaper, why pay more money for a lower spec old chip?.

 

[Someone Electro]

Unles his store is selling them realy cheap to get rid of them.

 

[bluehand]

the only pic I found is the 16F84

I need five (5) inputs, four (4) for 4 bits of data from the decimal-to-bcd encoder*, and one (1) as a "pressing notifier" (for 0000 input at the 4 bits of data).

I need seven (7) outputs, four (4) for bcd output function, and one (1) for each (three total (3) ) latch enabled input of the drivers.

the idea is like this:

- Keyboard, with 10 button
- Decimal-to-bcd encoder
- Three seven segment leds.
- Three 4511 or 4543 display drivers (right, center and left). These drivers are latched at their inputs. The lacth function is controlled by a LT pin. (low for latch enabled). They have another interesting feature: they output blank when the input is 1010,1011,1100,1101,1110,1111.
- One circuit, including pic16f84

Counter A=0

1.- When circuitry is turned on, pic sends to its otputs pins "1111", the displays show blank, and then the pic activate the latch function of the drivers.

1.- pressing a button in the keyboard. The button is encoded in bcd code, and this code appears at the input of the pic. The pic reads this input, thanks to the "pressing notifier" signal.

2.- the pic disables the latch function of the display on the right, and sends to itself otputs the bcd number that was entered at its input. When the driver shows the number entered, the pic activate again the latch function of that driver. A=1

A<3, continue.

3.- pressing a button in the keyboard. the pic receives the number in bcd code and performs two operations: (a) deactivates the latch in the center driver and sends the first bcd number entered in 2.- to its output. Then, when the center driver shows the number, the pic activates the latch function of that, and b) repeat 2.- with the number at its input. Two numbers are shown in the displays. A=2

A<3, continue

4.- pressing a button in the keyboard. the pic receives the number in bcd code and performs the same operations shown above, first with the left driver, then with the center driver and then with the right driver. Three numbers are shown in the displays (I hope this! :roll A=3

A=3, is not possible to enter more bcd numbers to the drivers. The reset function send the program to 1.-




It will be possible that dream ? ( = How can I translate this algorithm to a program? or. can I? )


NOTE:
* the "Decimal-to-bcd encoder" encodes the input button entered at keyboard, into a bcd code of 4 bits. I make an experimental one made only of 1n4148 diodes and it works perfectly!.

 

[Someone Electro]

There is a problem.

you need 4 pins to contol an single 7 segment driver and you have 3 so that makes 12 pins for the 7 seg. displays and that leavs 4 pins for the key pad.

If you can get an "matrix keypad to 4 bit" chip you got it solved.