Sequenced / delayed "lights on" with LM3915

Thread Starter

Laszlo Szabo 1

Joined Feb 27, 2017
13
I am looking for some kind of simple "signal generator" circuit that drives the LM3915. No, I do not want VU meter :)
I am on a project for a model, where I want the houses to be switched on after each other with 10 sec or max a minute delays till all would be ON.
And of course, they should stay illuminated till they will be switched off. The number of outputs of the LM3915 is OK, however, I need to use some MOSFET anyway. I have several LEDs in the houses and also some in a chain because there are many buildings.

I was thinking about LM3915but cannot find anything that drives it, just VU meters... a lot of VU meters :D

The first thing I wanted, switch the houses on and off periodically, you know, as a town looks like normally at night.
But doing both, I have only one idea:
I probably would use an Arduino and type some simple code to achieve both of the above-mentioned possibilities.

However, if someone has any idea, I am open-minded because I like to learn very much. And I will see which one is better.
Thank you.
 

LesJones

Joined Jan 8, 2017
3,905
You just need to ramp up the DC voltage to the input. As the LM3915 has a logarithmic response you would need to generate a logarithmic ramp id you want an equal time interval between lighting each light.
There is a device in the same family of chips that has a linear response. If you used this a simple linear voltage ramp would work and this would be easier to generate.
This method seems to be more complicated than necessary. I think using a shift register would be a better solution.
Edit. The device with linear response is an LM3914.
Les.
 
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bassbindevil

Joined Jan 23, 2014
641
So, you wouldn't consider an Arduino? A generic Pro Mini can still be found for about $5 on ebay. It doesn't have a USB-to-serial interface on board for programming it, but for a couple of bucks there are fake but functional FTDI FT232RL boards.

There seems to be an ample supply of LM3915 chips out there. Some may be real old stock, others are from a mysterious Chinese chipmaker that has revived a bunch of classic linear ICs. http://hlf-ic.cn

If you want lights that go on and off seemingly at random, the 4060 is a binary counter that has a built-in clock, so it's a one-chip solution for doing blinky lights.
 
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eetech00

Joined Jun 8, 2013
3,418
I am looking for some kind of simple "signal generator" circuit that drives the LM3915. No, I do not want VU meter :)
I am on a project for a model, where I want the houses to be switched on after each other with 10 sec or max a minute delays till all would be ON.
And of course, they should stay illuminated till they will be switched off. The number of outputs of the LM3915 is OK, however, I need to use some MOSFET anyway. I have several LEDs in the houses and also some in a chain because there are many buildings.

I was thinking about LM3915but cannot find anything that drives it, just VU meters... a lot of VU meters :D

The first thing I wanted, switch the houses on and off periodically, you know, as a town looks like normally at night.
But doing both, I have only one idea:
I probably would use an Arduino and type some simple code to achieve both of the above-mentioned possibilities.

However, if someone has any idea, I am open-minded because I like to learn very much. And I will see which one is better.
Thank you.
You didn't say how many lights.
A digital approach would be easier in terms of timing and expansion.
Use a clock generator, shift register or counter, and mosfet array driver.
If you want the lights to sequence on, then off, an up/dn counter could be used instead.

An LM3915 or LM3914 would require a linear ramp generator. If expansion is required, the ramp would need to be adjustable so as to maintain the LED timing. If you want the lights to sequence on, then off, the ramp would need to be a triangle generator instead.
 

Reloadron

Joined Jan 15, 2015
7,085
Twenty or more years ago, using discrete components I would have used an LM3914 driven by a sawtooth generator where the sawtooth ramp time determines the rate lights turn on. Today I would just any of several Arduino chips (or similar). A few lines of code and sequentially turn on LEDs. If each LED or set of LEDs for my buildings needed more current I would just use some transistor drivers like a 2N2222 or depending on load current maybe a Logic Level MOSFET like a FQP30N06L. Today writing a few lines of code beats using discrete components. Also as mentioned the LM3915 is non-linear (logarithmic) and been out of production for years. :) Yes, you can also use a decade counter divider and make a clock circuit but again today I am going the uC route.

Ron
 
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MisterBill2

Joined Jan 23, 2018
13,808
To provide the slow switching that the TS is asking for, a very simple RC circuit with a higher value capacitor charging through a high value resistor will provide a suitable function. and because the charge slows as the voltage rises the timing should be close to linear. the capacitor will be 1 or2 microfarad, the resistor will be a few megohms, and the charging voltage just a bit more than the selected reference voltage. the lights will come on in sequence and stay on until the charging voltage is removed, at which point they will slowly switch off.
 
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