First timer, advice for driving seven 7 digit displays and two 8 bits PLLs

Hello. Sorry for the long post.

I stumbled upon Arduino as I was buying some TTL chips to build a decade counter for a project. Having no knowledge of programming and very little with µprocessors, I usually stay away from it and build most of my stuff with gates and basic logic circuits.

I am upgrading an old radio that has PLLs and VCOs controlled by contact closures and I was planning to build decade counters with 74193 to drive the PLLs and program some EEPROMS to have the correct output data to 7 segment displays.

Now at almost 50yo it's time for me to embrace the new world and get into programming, I got a glimpse of what can be done besides counting up and down and I'm very excited.

What I need to do is control two PLLs with 8 bits of data each and also display this data in form of frequency readout on the displays. Basically it's like a tuner, you scan up or down and the display tells you what frequency is set.

I'm including a sketch of what I was planning to do with TTL or CMOS logic and I guess I need for that a Mega 2560

Now my questions. Is it really complicated? I'm not stupid but I am really a newbie, really. I'm very proficient in electronics, I'm at it for more than 30 years, but I never did programming, I'm programming some Extron stuff for audiovisuals and DSPs but no command line whatsoever.

Do I have the right unit? Can I pull it off?

Thanks for any pointers.

I usually stay away from it and build most of my stuff with gates and basic logic circuits.

This is what you wind up with when you stay away from uProcessors and just use gates and basic logic circuits.

Have you considered using the Max7219.
It is SPI based and only needs three pinsfrom the uC. to control EIGHT 7-segment displays. (SEE ATTACHED FILES)

MAX7219-MAX7221.pdf (491 KB)

max7219_tutorial_pre_c.pdf (186 KB)

I was wander, where PLL comes from? Looks like it has noting to do with phase-locked loop, is there another abbreviation?

Magician: I was wander, where PLL comes from? Looks like it has noting to do with phase-locked loop, is there another abbreviation?

In fact those are the inputs of the "divide by n" part of a PLL/VCO system. The first VCO generates around 15-17MHz in 10kHz increments and the second around 30MHz in 1kHz increments.

It's all part of the frequency generating system of a dual conversion receiver.

raschemmel: Have you considered using the Max7219. It is SPI based and only needs three pinsfrom the uC. to control EIGHT 7-segment displays. (SEE ATTACHED FILES)

Thanks, but I don't see how this can be of any help to my project.

Thanks, but I don’t see how this can be of any help to my project.

What about PCF8574 I/O Expanders ? (see attached) . That is what you need , right ? (I/O)

PCF8574.pdf (1.3 MB)

Magician: I was wander, where PLL comes from? Looks like it has noting to do with phase-locked loop, is there another abbreviation?

A PLL (phase-locked loop) can be used as a frequency synthesizer. The basic idea is if you have a reference signal "ref" of frequency, f, you can use the PLL to align every rising edge of ref to every Nth rising edge of the PLL output "out". That is, you use logic to mask all but the Nth edge of the signal "out". Thus the frequency of "out" is f*N. In the same way, you can mask all but the Mth edge of "ref" to align with "out" to produce the frequency f/M. The two techniques can be combined to produce f*N/M.

Vous etes d'accord?

Vous etes d'accord?

Oui, bien sur. I was confused with a drawings, where PLL bloc is really looks like ULN2803, and part of the column driver for LED's.

To OP: IMHO, it would be easy to set two 8-bit's port on arduino Mega, in order to control PLL's, as I can guess, they require no current on inputs. The same time arduino UNO board and some IC as port extender may be cheaper solution. MCP23008 or MCP23017 for example.

Regarding LED's 7-segments tablo, using external driver is not an option, you have to use transistors / ULN2803/ or specifically designed driver MAX7219 etc, just because output current of the arduino limited by 20 mA.

Magician:

Vous etes d'accord?

Oui, bien sur. I was confused with a drawings, where PLL bloc is really looks like ULN2803, and part of the column driver for LED's.

To OP: IMHO, it would be easy to set two 8-bit's port on arduino Mega, in order to control PLL's, as I can guess, they require no current on inputs. The same time arduino UNO board and some IC as port extender may be cheaper solution. MCP23008 or MCP23017 for example.

Regarding LED's 7-segments tablo, using external driver is not an option, you have to use transistors / ULN2803/ or specifically designed driver MAX7219 etc, just because output current of the arduino limited by 20 mA.

Thanks for your answer. No the PLLs require no current, they are just logic inputs, as for the displays, I was planning to use drivers and external supplies of course, this drawing was just an illustration of the desired functions I was looking for.

Oh well, I guess I’ll just try to figure it out myself. :slight_smile:

Have you seen playground?

Seven segment displays (See also the "LED Multiplexing" sections. Here we have displays supplied with character generating control circuitry, minimizing the work you have to do.)

http://playground.arduino.cc/Main/InterfacingWithHardware#Output

Ok, thanks all for your help, but I guess I wasn't clear enough.

The radio is existing, the PLLs and 7 segment digits are existing, I want to preserve all this, I only want to get rid of the old control system that used rotary switches and 7447 for the displays.

For now I will order one arduino mega and start playing around to get the feel of it.

Thanks!