# [SOLVED] led clock display



## geosman (Sep 15, 2007)

Can't find anything on web about reusing/recycling the digital display from clock radios and the like. I've heard these do not use the common cathode/anode 7 segment approach I am familiar with. Can someone enlighten me and/or suggest some websites that address this?


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## Done_Fishin (Oct 10, 2006)

*Re: led clock display*

define the displays that you need to reuse .. are they just numeric or alphanumeric ? Are they LED or the other type whose name escapes me right now. leds use sim ple circuitry whilst the other type require a negative voltage and offset heater voltage.

you should be able to find some sort of part number on the display, Google the part number and find a data sheet. Then use it for whatever purpose comes to mind.


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## geosman (Sep 15, 2007)

*Re: led clock display*

The current device I have is a 4-MT-185G (a 10 segment unit) which I don't know if there is a datasheet for it. I took it out some time back and usually do check for a datasheet so suspect none exists. Think you may be thinking about nixie tubes. 
My interest is in removing some numeric only LED units from a failed clock radio.


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## Done_Fishin (Oct 10, 2006)

*Re: led clock display*

"Nixie" was in my thoughts but wasn't sure .. it's been so long since I did anything with them.

LED numeric displays come in two basic designs

Common Anode and Common Cathode

If you use a Digital Multimeter on Diode you will be able to see what type you have by looking for a common pin that lights up the diodes individually. Just change Polarity of the test leads should nothing show up. Another way would be to use a battery with a resistor that keeps the current to a max of 5mA. 2mA is a good figure to work with. Don't exceed 5 volts in reverse bias in case you burn an LED.

You will also be able to figure out what pin feeds which segment.

there are IC's in both CMOS & TTL that will allow you to feed a binary code to the chip and display the decimal character (binary count decimal decoder). Look on the net for 7 segment led circuits.

heres one to start with 

http://www.play-hookey.com/digital/experiments/seven_seg_driver.html


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