new to circuits, have a question.

Discussion in 'General Electronics Chat' started by lostissues, Feb 17, 2009.

  1. lostissues

    Thread Starter New Member

    Feb 17, 2009
    3
    0
    My question is this; I have been trying to find a way to use a momentary push button to trigger a relay to turn lights on in my truck. I have settled on this circuit here http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm#toggle3.gif I have everything working but like he said in his description if you hold the button (in my case for about 1/4 of a second) the relay re-latches. He said how to minimize that problem but I cannot figure it out. He says to add a resistor from the base of the transistor to ground. I cannot figure out if he means add another one on top of the 820 ohm already in his diagram or to change that resistor to something else or if the circuit he drew already has that implemented into it.
    I am using the monostable version of this relay in the circuit: http://www.yankeesurplus.net/PDF/Item_510/V23079.pdf and I plan on using this relay to send a negative signal to a regular 30/40 amp automotive relay and use that relay to trigger the lights.
    also because I'm using this in a truck where the voltage will vary should I worry about that? or will it be OK if its around 12 volts give or take a couple volts?
    and lastly the 1000uf cap, I picked one up a radio shack and it is a 35v cap, Is this overkill and should I look for a 1000uf 12v cap?

    any help would be greatly appreciated.
    Thanks,
    Jonathan
     
  2. Mike33

    AAC Fanatic!

    Feb 4, 2005
    349
    25
    Try adding a potentiometer in parallel with the 820 ohm resistor ('additional resistor'); try a 1K, and if that doesn't do it, go to 10K. Dial it in until the relay doesn't toggle as fast. Like the site says, if you can get it to behave for about 1 full second, you're in usable territory. Once it works with the pot, remove pot and measure the resistance and replace is with a resistor. Or just use a trim pot soldered in the circuit to adjust and forget. You can put a drop of silicone on it once set to keep it from re-adjusting itself.

    Make sure to measure the voltage across the relay when engaged like he suggests, having the voltage in between the pull-in and dropout levels.

    Your caps are fine at the 35V rating, that's really only an issue if they were VERY much off. I think the caps will smooth minor voltage variations and the alternator is usually regulated; you'll have to try it to know! That can be another topic if there is trouble...

    Hope this helps!
     
  3. Dan2

    Member

    Oct 16, 2008
    19
    0
    i would just use a flip flop to control a transistor to turn on the relay. with a JK flip flop, keep both inputs high and use the push button for the clock pulse, and hook up transistor to one of the outputs.
     
  4. lostissues

    Thread Starter New Member

    Feb 17, 2009
    3
    0
    I don't have a potentiometer but i do have a lot of resistors so i can try adding in different value resistors and see if that make any difference.

    as for the flip flop I have heard of that before someone on another site suggested it. the only thing is that after a quick google search I kind of get how it work and how I would implement it but I'm still not sure on exactly what it is. all i can seam to find is a diagram of some nand and nor (I think that right) gates. is this something that I would have to program onto a microcontroler? I had contemplated doing this an looked into the Arduino board but figured that that would be over kill for just turning on a few lights. also I got very confused by microcontroler I have no idea why but I just cannot grasp some of the concepts. with the circuit I posted about it was something that I was mostly able to wrap my head around. I don't know much about electronics but I know a couple of basic things and was able to figure out how most of this circuit works.

    Thank you for your help so far!
    Jonathan
     
  5. Mike33

    AAC Fanatic!

    Feb 4, 2005
    349
    25
    If you've gotten this far, Jonathan, I'd just finish it, lol. You can get flip-flops in an IC package just like the 555, but you'd have to order them from a supplier. Radio shack doesn't carry much these days! They do have potentiometers, though, so maybe grab a couple, it will make life easier!
     
  6. lostissues

    Thread Starter New Member

    Feb 17, 2009
    3
    0
    well I added another 820 ohm resistor in parallel with the original 820 ohm resistor and when I press and hold the button the relay will either click off after about 3 seconds or it will not click off at all. so this is a desirable outcome. as for the flip flop, I will make this circuit for now and maybe later on try it out with using flip flops. it looks like it would be a much simpler circuit.

    Thank you guys for all your help.

    Jonathan
     
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