# Small Circuit needed for New Product Design - Help!

#### BobK

Jan 5, 2010
7,682
I just paged through the LCD driver section of PIC you found. What they go through the multiplex is mind boggling. You have to make sure that each pixel never sees more of 1 polarity than other and they go to great lengths to make this happen. Interesting reading.

A periodic wake-up would also work, but I really like the idea that the PIC will keep the LCD bits flipping even when it is sleeping. A 28-pin SSOP is still pretty small.

Bob

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,508
why not look at one of the cheap lcd modules?

#### BobK

Jan 5, 2010
7,682
What kind of module? Like a text display?

Bob

#### D Hancock

May 23, 2014
16
As far as I can tell, the smallest PIC that has an LCD driver built-in is a 28-pin one anyway.

Edit: I see what you're getting at. With a non-multiplexed display, you don't need any special LCD driver in the microcontroller. You just have to get the code to flip the outputs between 60 and 180 times per second. Given that the code barely needs to do anything else, that wouldn't be a problem. So you could probably use a generic 24-pin or 20-pin device with that particular LCD.

I would like to get a decision from the OP on LCD vs. LED first though.

And on that subject, there's another difference I forgot to mention - the required supply voltage. For an LCD a 3V supply could be appropriate, but for an LED display, the supply voltage may need to be significantly higher. It depends on the segment forward voltage.

Kris, I haven't had time to digest the latest responses. In regard to the LCD vs LED - at least for the prototype I've decided to go with LCD. LEDs require too much power.

#### KrisBlueNZ

##### Sadly passed away in 2015
Nov 28, 2011
8,393
Right, fair enough. It looks like the LCD you found will work nicely from 3V and can be driven from any micro with enough I/O - 15 outputs for that display, or 17 if you want to drive the decimal points too. Add between 1 and 3 pins for the pushbuttons, and you could use any PIC or similar small microcontroller with 20, 24 or 28 pins. I suggest you leave a few pins spare for future expansion.

You asked about the other small components. With that LCD, you won't need many! One or two decoupling capacitors, and possibly a few resistors if you don't have one pin per pushbutton. You could probably power it from a 3V lithium coin cell e.g. CR2032.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,508
What kind of module? Like a text display?

No, one of the "graphics" ones. There are a number of small screens with built in controllers, some designed for phones. I've used one as the display for a little 2.4GHz scanner.

However I missed the link for the LCD display the OP posted (in my defense, I was on public transport at the time, jostling for position to get off the train).

The display he has found seems to ne quite a reasonable price.

May 23, 2014
16
Kris,

Jan 5, 2010
7,682
Not in the area. If I were to do it, I would charge $500 to deliver one prototype PCB (not to a specified size and shape) and the code. Is this in the range you are thinking? Bob #### D Hancock May 23, 2014 16 Not in the area. If I were to do it, I would charge$500 to deliver one prototype PCB (not to a specified size and shape) and the code. Is this in the range you are thinking?

Bob
A little outside my budget but I'll get back with you to confirm. I'm completing the prototype so I can actually get the check to make a more polished unit.

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