Help me with my LED Voltage Level Indicator.

[eduardouy]

I made a regulated variable power supply with an output of 0-30V and 1.5A max. I want to put a voltage level indicator using a LED. I saw a sample in a book with a bipolar junction transistor and a zener diode but i cannot fully draw the circuit.

Please help me to design a circuit of this when every 3V from the output of power supply 1 LED will turn on. Then when 30V from the output, 10 LEDs will turn on.

Thank you in advance.

 

[canadaelk]

The easiest is to do this is with the Nat. Semi. LM3914. All the info you need is in the datasheet. I, however would use an inexpensive ($20 or so) digital with 3 1/2 digits, set to 200V readout. E

 

[alec_t]

A bargraph display chip will drive 10 LEDs the way you want. Google for that.

 

[eduardouy]

I search for LM3914 but i cannot understand where will i connect it to the power supply. Please help me.

 

[ronv]

Why don't you just buy an inexpensive meter it would be more accurate and be multipurpose.

https://www.radioshack.com/family/index.jsp?categoryId=2032305

 

[eduardouy]

It's a project and i am required to put a LED voltage indicator. Thanks

 

[alec_t]

The datasheet for an LM3914 from any reputable manufacturer probably has an example of how it's used. Google 'LM3914 datasheet'.

 

[Boncuk]

All wrong - more or less.

Ericgibbs has put in an LM3914 simulating program. Just enter the necessary values and you're done.

Check out the Blogs!

Boncuk

 

[eduardouy]

Sorry im a ultimate noob in reading datasheet. I used the ericgibbs calc, but i dont know now how will i put a a voltage in V+ and in RHi. Can you help me with these? I really need a Led Voltage Level Indicator. Thanks.

 

[ericgibbs]

Sorry im a ultimate noob in reading datasheet. I used the ericgibbs calc, but i dont know now how will i put a a voltage in V+ and in RHi. Can you help me with these? I really need a Led Voltage Level Indicator. Thanks.

hi,
In order power the LM3914 and LED's you need a voltage supply, say 9Vdc or 12Vdc supply.

Do you have a fixed voltage supply.?

 

[eduardouy]

hello ericgibbs,

i have with me a adjustable voltage supply, may Vout is from 1.25-30V using LM317. Please help me to design a circuit of this when every 3V from the output of power supply 1 LED will turn on. Then when 30V from the output, 10 LEDs will turn on. Thank you.

 

[eduardouy]

Please FIX my design

Here is my designed circuit after using the simulation for lm3914. When im using bargraph mode, the 10 LED are not working perfectly working. The LEDs are mostly dim. Please see my attachment.
What's wrong with my circuit?

 

[eduardouy]

Please check my circuit design.

To those who helped me, thank you so much. I've come up to this circuit design and it running in my proteus. But i would like to ask for you spare time to check my design. Here it is.

I need to transfer this in pcb as soon as possible because the submission of this is nearly approaching.

Thank you so much.

 

[ericgibbs]

hi,
That circuit is NOT suitable, there is NO mains transformer shown, also there are errors in the remainder of the circuit.

You require an mains isolated power supply that can supply a DC voltage at 0.25A , the DC voltage of the supply can be from 9V to 20V.
Let me know which power supply you have available and will post a circuit diagram.

If you rectify and smooth 24Vac you will have a DC voltage of 35Vdc, the LM3914, is rated at 25Vdc max.

 

[eduardouy]

If you rectify and smooth 24Vac you will have a DC voltage of 35Vdc, the LM3914, is rated at 25Vdc max.

Oh. Can i just put a resistor so that i can i can put 25Vdc max to the LM3914. If not, so i can't use LM3914 for a LED Voltage level indicator. My power supply is rectifying 24Vac and the out put is from 1.25-30V 1A. What will i do to put a LED Voltage indicator? Using BJT with zener? Please help me with the calculations.

Here is my power supply.

 

[ericgibbs]

hi,
Add a 7812 regulator as shown in this image, use it to power the LM3914.

 

[eduardouy]

hi,
Add a 7812 regulator as shown in this image, use it to power the LM3914.

What voltage rating will i use for the 100nF and 22uF Capacitor? Thank you so much sir.

 

[ericgibbs]

What voltage rating will i use for the 100nF and 22uF Capacitor? Thank you so much sir.

hi,
=> 25Vwkg will be OK.

 

[eduardouy]

Where am i going to connect RHi?

 

[eduardouy]

Hi,

I've follow your suggestions and my problem now where will i connect RHi which 30Vhigh base to the lm3914 simulator.

Here it is. Is the circuit correct?