Led Signs
Posted on 12/01/2009 11:23 am by admin
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How to make a led price sign?
Looking to make a 3 digit price sign (ex. 2.59) out of 12 volt, 12" led light bars, using 7 bars for each digit. Want to be able to change each number. How can you do it or where can I find plans for the controller. Thanks
An after thought: you could use toggle switches for each segment or you could go as I wrote it before.
You can start looking at BCD-to-7-Segment-Decoder (7SD) IC's.
Each segment of LEDs will consist of enough of them for the 12" bar.
You need one resistor in series with each LED.
All LED/Resistor combinations in each bar will be in parallel.
The voltage across each LED will be about 1.7 volts DC. If you use a 12VDC power supply, each resistor will have to drop 10.3 volts. Depending on the LED you'll have to find the current they need for a given brightness.
Supposing 20mA (0.02 A) for each LED, 10.3V/0.02A=~510 Ohms. Recalculate for your currents. Power dissipation on each resistor = E x I = 10.3 x 0.02 = 0.21 watts, use 1/2 watt resistors.
The 7-Segment-Decoder may not be capable of driving the load of all LEDs in each bar, so you may need buffers.
You'll need additional electronics to drive the 7SDs, depending on how you want to set the digits for the prices. You could use toggle switches for each 7SD input.
Get data-sheets for all components.
Visit http://www.national.com/ds/MM/MM54C48.pdf#page=1 for a 7SD data-sheet.
You could buy these parts from mouser electronics, http://mouser.com/
If you want more details, email me. Now, since you do not allow email, I couldn't reply to you unless you give me your email.
led sign
