Help with 555 timer circuit please!

Discussion in 'The Projects Forum' started by nodestination1, Nov 6, 2012.

  1. nodestination1

    Thread Starter New Member

    Nov 5, 2012
    Hello Circuits Forum people, I’m using a 555 timer to control a small 12v motor. The motor moves a rod from an up to a down position, and the goal is to allow the user to change the height at which the rod stops. The time it takes the rod to travel from top to bottom is about 1.5 seconds.
    So far here is what I’ve done:
    I purchased a pre-assembled velleman 555 timer circuit and replaced the “pulse” trimmer with a 5k potentiometer. I then turned the pause trimmer to the max-about 60 seconds. This gave me the 0-1.5 second time interval I was looking for. The circuit works well, but I'd like to make a few changes to the pre-assembled version.

    What I need help with:
    The velleman mk111 kit is set up for astable operation – it has a pulse trimmer and a pause trimmer. I want to use the mk111 kit, but set it up for monostable operation. I want the circuit to pulse once and then stop until 12v is applied to the motor again.

    I’m mechanically inclined, but have little to no experience with electrical engineering. I can solder and assemble a circuit, but I cannot read a circuit diagram very well (or... at all). It all kind of looks like jibberish to me, and after a while I feel like I’m reading Russian.
    I’ve done a good deal of research on the subject, but can't figure out what I'd need to do to make the mk111 circuit work the way I want it to.
    I would be eternally grateful if someone could give me instructions – possibly with pictures – on how to use the velleman mk11 kit but remove the pause trimmer and set it up for monostable operation. I can post circuit diagrams and pictures if needed.

    Thanks in advance!

    Informative website on 555 timers that I've been using
    ^very large image of the circuit in question
  2. Wendy


    Mar 24, 2008
    This site has some article on 555s too, I wrote them. A lot of them have been incorporated in the AAC text book shown on the top of the page.

    Bill's Index

    3. The 555 Projects
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
    Apparently, you want to change the MK111 operation from astable to monostable operation. Although I haven't looked at the PCB layout, I believe this is possible, but it won't be easy. It will require some components to be removed and replaced, some tracks to be cut on the PCB, some holes to be drilled, and some flywires to be added. I build a lot of circuits from kits and from scratch, and I can assure you that, at its best, the result won't be pretty; at worst, you could ruin the MK111.

    It would be much easier to buy a kit or an assembled circuit to do what you want. It actually would be easier to build the circuit from scratch on a piece of perfboard. It might well be easier to remove the relay and the 555 from the MK111, and use them to build the circuit on perfboard.

    Do you have a good soldering iron, a solder sucker, some solder removal braid, small needle nose pliers, small wire cutters, and some way to hold the PCB while you heat components and try to tug them off the board?
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Turns out to be pretty easy?? The dimple on 555 marks pin 1, cut trace at, or near, pin2, pin 6 should still go to + of C3. Understand timing is to start at power-up-ok then add a resistor from + supply, + side of C2 or Pin 8 or4, 10k to 100k,[ color code of 10k like 1k except third band is orange instead of red ], connect a capacitor, just like C1. .1μF to other end of resistor, free end of cap to ground, like pin 1. Connect pin 2 with short jumper wire, to junction of 10k & .1 cap. If you donot have a cap, seperate C1 from pin 5 & use it, leave pin 5 floating.
    If you have trouble send a photo of back side of PCB.
    Last edited: Nov 9, 2012
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Maybe this will help with questions.