Saturday, April 13, 2013

Power up down Sequencer

Whether you’re speaking about a residence cinema  or a computer system, it’s very frequently the case  that the more than a few elements of the machine have  to be fliped on or off in a relatively explicit order,  or at least, routinely. Constructing this  sort of automation system is neatly inside the  functionality of any electronics enthusiast invaluable of the identify, however on this ‘all-digital’ age,  many of the circuits of this kind to be found  in newbie electronics magazines or web-sites use a microcontroller. Even although that  is indeed a logical solution (in  extra meanss than one!), and you  would probably even say the easiest one, it  does pose issues for all those  people who don’t (yet) have the  amenities for programming these  kinds  of  IC.  So  we  decided  to  offer you now an method that’s  very different, because it only makes use of a  simple, low cost, commonly-avail-able analogue integrated circuit,  which in fact doesn’t have to  be programmed. Our project in  reality makes use of as it’s ‘brain’ an LM3914,  a familiar IC from National Semiconductors,  usually  used  for  using  LED  VU  (volume  unit)  meters. 

Circuit diagram :

Power-up/down Sequencer Circuit Diagram

Before taking a look on the circuit  for  our  mission,  let ’s  just  remind ourselves that the IC has  one analogue enter and ten out-puts supposed for riding LEDs.  It can function in ‘point’ mode,  where the LEDs light up in flip,  from first to last, depending on  the enter voltage, but just one LED is lit at  any supplyn time. Alternatively  it will most probably function  in ‘bar’ mode (this is the mode usually used  for VU meters), and on this case, the LEDs light  up one after the other, in any such means as to create a strip of light (bar) that is longer or  shorter according to the enter voltage. This is  the mode selected for the LM3914 in the circuit described in some detail under. 

So as in an effort to control the AC energyed equipment  our  sequencer  is  meant  to manage, we're using solid-state relays — four, in our example, although which you can reduce or elevate this number, as so much as a most of ten. Since the enter instruments in solid-state relays are LEDs, they can be driven right away with the help of the LM3914 outputs, for the reason that that’s precisely what they’re designed for. As best 4 relays  are on hand, these are unfold across out-puts L2, L4, L6, and L8, however you can choose  any arrangement you prefer to go nicely with the quantity  of relays you want to have to make use of. 

Resistor R7 connected to pin 7 of the LM3914  units the current fed to the LEDs by means of the LM3914  outputs. Here, it’s been set to 20 mA, due to the fact  that's the price anticipated by the solid-state  relays chosen. The input voltage utilized to  pin 5 of the LM3914 is none instead of the  voltage present throughout capacitor C1 — and  that is the place the circuit is ingenious. When  the change is set to ‘on’, C1 charges slowly  thru R5, and the LEDs of the solid-state  relays on the outputs gentle one after another  as this voltage raises; in this approach, the gadgets  being keep watch overled are energyed up within the order you’ve chosen. To energy-down, all you have  to do is flip the change so that C1 discharges  through  R5,  and  the  LEDs  go  out  in  the  reverse order to that wherein they had been lit,  in turn energying down the devices connected to the solid-state relays. Easy, isn’t it? If you’re not pleased with the sequence velocity,  all you need do is increase or reduce the  value of R5 to be in a place to alter the pace one  manner or the different.
The circuit needs to be energyed from a volt-age of around 9 to 12 V, which doesn’t even  wish to be stabilized. A easy ‘plug-top’,  ‘wall wart’ or ‘battery eliminator’ unit will be  good, just so long as it is able to supply-ing enough current to power all the LEDs. As  the LED present is set by R7 to 20 mA per LED,  it’ll be simple for you to work out the current  required, according to the collection of solid-state relays you’re the use of. 

In our prototype the kind S216S02 relays  from Sharp have been used, primarily as a consequence of they  proved comfortably on hand via mail order. They even have the good thing about being compact,  and their switching capacity of sixteen A means  which you can dispense with a heatsink if you’re  the use of them for a computer or residence cinema  system, the place the present drawn via the vari-ous gadgets will more than likely be expected to stay under  1 A. These solid-state relays should be safe by a fuse, the score of which wants to  be chosen according to the current drawn  through the tools being powered. 

Also no longere the presence across the relay time periodinals of a VDR, sometimes called a GeMOV or  SiOV, intended to protect them from any spurious voltage spikes. You can use any sort  that ’s intended for operation on 250 VAC  with none problem. The prices of fuses F1  to F4 are after all going to rely upon the  load being secure. 

Construction of the circuit shouldn’t present any particular problem, however as the solid-state relays are connected right away to AC  power, it's very important to install it in a fully-insulated case; the case can additionally be used to  mount the energy outlet sockets keep watch overled  with the aid of the circuit. Note that sockets are female  elements.
Let’s simply finish this description with the sole  restrict imposed with the help of our circuit — but it’s  very simple to agree to, providen the intended  use. In order to remain brought about, the solid-state relays must elevate a minimal holding  present, which is 50 mA within the case of the  instruments we’ve selected. In sensible terms,  this just means that each and every of the devices powered by means of our sequencer should draw as a minimal  50 mA, or in different phrases roughly 12 VA at  230 VAC, or 25 VA at a hundred and twenty VAC.

Author :Christian Tavernier

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