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# Help designing a simple LED table

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#### RuSty420

##### New Member
Hi all, first post here!

I am a beginner to circuitry and DIY electronics and I had a simple project in mind that is something I can use to both educate myself about electronics and make something crafty!

I want to make a very simple NON-interactive LED backlit glowing end table / nightstand. The table is going to consist of a wooden frame with 3 isolated chambers, each housing different color LED's, and a glass panel sitting ontop.

Here is an quick sketch (birds-eye view) of my design:

3ft(w) x 10in (h)

The brown frame represents the wood skeleton, the colored squares are the three chambers housing the LED's. The glass panel is the same measurments (3' x 10") and rests directly on top of the panel. In between will be a sheet of rice paper or similar medium to diffuse the light.

I plan to have 9 LED's in each square, organized by color (red, yellow, green). The three squares will be wired to a simple on off switch and powered from the wall.

So now, onto the questions:
• 1. How do I correctly setup the LED circuit so that the LEDs are in groups of 10 with each group linked to the on/off switch?

• 2. For 27 LED's (9 red, 9 yellow, 9 green) what kind of DC power supply should I use to power from a wall socket?

Thanks for looking,
-RuSty

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make 9 leds in series and grop it as one and 3 such groups. you need a power supply of
9x1.3V(depends on the led specs, 15V can be used) and a series resistor to limit current for each group.

the current capacity can be not less than 3 x led rated current, if 20mA is required for one LED (since its in series its same for a group) then need 60mA minimum.

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1. How do I correctly setup the LED circuit so that the LEDs are in groups of 10 with each group linked to the on/off switch?
Why groups of 10?

he has total 30 LEDs and installed in 3 blocks, so in one time 10 LEDs are switched on, hope thats the reason he mentioned as group of 10.

he has total 30 LEDs and installed in 3 blocks, so in one time 10 LEDs are switched on, hope thats the reason he mentioned as group of 10.
.
2. For 27 LED's (9 red, 9 yellow, 9 green) what kind of DC power supply should I use to power from a wall socket?
As I read it, he has 9 red, 9 yellow, 9 green and wants them in groups of 10.

Unless he is working on two different designs.

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make 9 leds in series and grop it as one and 3 such groups. you need a power supply of
9x1.3V(depends on the led specs, 15V can be used) and a series resistor to limit current for each group.

Hi mbarazeen,

only IR-LEDs have a forward voltage of 1.3V. Green, yellow and orange LEDs normally have an Uf of 2.4V, red LEDs are generally 1.8V.

So for the green and yellow boxes the OP would need a power supply with at least 21.6V output voltage, for the red box 16.2V would suffice, provided the OP wants to use 9LEDs in each box.

Here is a schematic how to connect the 27LEDs to a power source of 7.5V, rated current output not less than 200mA.

Boncuk

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, yes you are correct its 9 only i made a mistake when commented. also of cause the voltage is fully depends on LEDs specs and i just told it as an example. what you have posted is a good configuration. thanks for correcting me.

also he can follow the bellow to calculate the value of resistors to be conected in series as follows.

R= (Vs - N.Vd) / Id where

Vs- source voltage
N- number of LED in series
Vd- rated forword voltage of one LED
Id - Rated current of the LED

keep the source voltage always higher than N.Vd,

when (Vs-N.Vd ) is higher it will give stable brightness over any small variation of the source voltage

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