LED Brightness Control Project

[Zordon]

Hi, i am building a dual tracking power supply for 0 to 15vdc and i would like to use 5 LEDS as power on indicators. However, i would like the LED's to get progressively brighter as the voltage goes up. So,
0V = min brightless
15V= Max brightness

If there is a simple electronic method i would like to hear it.

I would like to use a PIC but i am really new to programming.

The way im thinking of doing it is using a PIC16F628 as a volt meter, and have 6 different resistors connected in parallel to the LEDS. When a certain voltage is triggered a different output will turn on and in turn a different brightness.

Here is a picture of the front of my power supply. the leds will go behind the voltage adjustment knob to create a glowing effect.
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This is a schematic of my power supply

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[blueroomelectronics]

Canakits (and others) make a LED voltmeter based on an Intersil IC

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Or this design https://www.electronics-lab.com/projects/test/014/
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[carmusic]

i would use the pwm output on the pic (dont know if 16f628 have one) and change duty cycle with voltage using an analog input. That would be very simple and only use a transistor and 1 resistor at the output

for easy programming pic i use https://cq.cx/ladder.pl

 

[ronsimpson]

You want simple way.
15 volts = bright LED.
0 volts = dim LED.

LED 1 is on the front panel.
LED 2 is a "2 volt zener" to make a -2 volt supply.
R1 is to set 12mA.
R2 is to set the 10mA at 15 vots. You will get about 1mA at 1 volts.

Sorry no PIC!

 

[Zordon]

Sorry i guess you guys misunderstood me i have five LEDS that i want to hide behind a knob to give it a glowing effect.
Also one LED lights up at noticeably less brightness is it faulty?

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[ronsimpson]

Look at the LM3914. It drives 10 LEDs but can be used with only 5 LEDs. Tie outputs 1-2 together, 3-4, 5-6,7-8, and 9-10.= 5 LEDs

 

[audioguru]

Do you have the LEDs in series so they all share the same current?
Or are they in parallel then each one will have a different current and a different brightness?

 

[Hero999]

I've looked at the circuit and I have a couple of comments:

You need a higher voltage transformer than 14VAC or a much larger filter capacitor, to get 15V out at higher currents. To regulate proberly at 1.5A the LM317 needs the input voltage to be at least 2.25V about the output voltage at the absolute minimum, for optimum performance it needs to be at least 3V.


Note that the other characteristics on the datasheet are specified with the output at 3V lower than the input voltage.

Attached, is a simulation of a 14VAC transformer, with a bridge rectifier with a 2200:mu:F capcitor and a 1.5A constant current load connected. The output voltage dips below 14.4V which will produce a huge ripple voltage on the output of the regulator. Increasing the capacitor value to 22000:mu: increases the minimum ripple to 17.6V which is fine even though you won't get the best from the regulator. This assumes that you haven't got anything connected to the LM7805, if you're going to connect a 1A load to that as well, you need a huge 33000:mu:F capacitor.

Another thing is how reliable do you expect the voltage drop of those diodes to be? They won't be exactly the same as the reference voltage of the regulator and will drift a bit as the temperature changes. You can get round this by using another op-amp configured as a difference amplifier that looks at the voltage between the output and common pin on the LM317 and inverts it to the negitive value.