LCD to LED convertor

[mahesh_jo]

LCD digital clocks are very cheap and very common thease days. Blue LEDs are also flooding the market these days. Is it possible to take a LCD digital clock (wrist watch) and attach a blue LED to each segment of its 7 segments. We can supply additional power to drive the LEDs.

-Mahesh Joshi
Bhopal, India

 

[ljcox]

LED watch

It would be necessary to use a 7 segment driver capable of driving LEDs

 

[bogdanfirst]

i think that all you will need is a buffer circuit wich will just increase the power of the chip, to provide enough current to drive the leds.

 

[k7elp60]

LED driver

You may want to consider the ULN2001 thru ULN2004 series of IC's they are capable of interfacing PMOS or CMOS to LED's. I have build numerous digital clocks with PMOS IC's and have used the ULN2004 as segment drivers. Then used standard NPN or PNP transistors as digit drivers depending upon if the LED's are common anode or common cathode.

 

[Sebi]

All of described solutions work only with independent segment outputs. If the LCD is multiplexed (most of case), the driver signal is staircase, and decoding is more complicated as original circuit...

 

[elec_lover]

Besites multiplexing, there is another problem:
An LCD segment uses an alterneting signaal to extend the live of the LCD segment. The backplane is alternating and the segment changes too depending of on/off status of the segment:

an ON segment receives +- -+ +- -+ +- etc
an OFF segment receives ++ -- ++ -- ++ etc
were the left sign referes to the backplane voltage.

So you need an electronic circuits to convert this dynamic signal to
a (static) signal capable to drive a LED.
Look here: Driving an LCD segment.

 

[mahesh_jo]

Complicated!

Thanks for your comments. It seems that the instead going to LED through LCD is more complicated than building a LED digital clock direct. Isn't it?

-Mahesh joshi

 

[elec_lover]

Making a conversion will be complex, because for each segment
you must make a conversion.
Make a complete new is a better choise ? If you start from a clock chip.
Buying one could be the best solution.

 

[Nigel Goodwin]

Re: Complicated!

Thanks for your comments. It seems that the instead going to LED through LCD is more complicated than building a LED digital clock direct. Isn't it?

Yes, considerably more so!.

 

[Blueteeth]

I'm sure it can be done, its just a question of hassle As almost all commercial digital LCD clocks have a single chip to control everything, it seems the solution of decoding the raw 'LCD multiplexed segment signals' is the only way. I have an old LCD clock which seems to have a separate IC for the display, with the master clock IC simply providing what looks like binary data. That would of course make life easier, but wonderful cheaper engineering has merged all that into one fine little die.

Why not make your own clock!! Perhaps using just the housing of an original? It's probably best done with a microcontroller, but it has been done many times with off-the-shelve TTL logic. There are also specific IC's still available that are up to the task, but perhaps not easy to get hold of.

As much as I love blue LED's, they are everywhere these days. A custom RGB/colour changing clock is where its at Haven't done that myself, but I did mod a 320x240 graphic display with a RGB led backlight. its beautiful.

 

[r singh]

LCD to LED converter

Pse a ckt diag.how to convert a digital wrist watch (LCD) module into a large display digital clock