national diploma level engineering project

Discussion in 'The Projects Forum' started by redacejr, Dec 7, 2010.

  1. redacejr

    Thread Starter Active Member

    Apr 22, 2008
    i have been assigned a long term assignement due to 10th january to construct a desktop power supply.

    i decided to use an old VCR case as a body and have already installed 3 transformers inside giving 5v , 12v and 20v output using a single ground. it came really presentable with banana sockets and stuff. the only problem is i had 3/4 of the front panel of the unit is still empty.
    other students have been adding stepper motor controls , or h-bridges or binary generators.

    i have decided to add an astable timer that can control a binary counter or as a standalone. the problem i have already drilled the hole for the variable resistor , and i guess i screwed up.

    i cannot find an astable 555 timer circuit that uses only 1 variable resistor and gives a 50%
    duty cycle . about 0.1-100 hz variations would be good .

    thanks in advance because i do not have space to drill another hole for another variable res ,and it would only mean i would have to start again

    i only started my project early to enjoy my holidays and i messed up :(

    im fine with the binary counter circuit , i just have to hook it up to the 555 timer output and install the selector toggle switch :)
  2. jpanhalt


    Jan 18, 2008
    I think one of Bill Marsden's 555 circuits can do 50% with a single potentiometer. If not, check Fairchild's application note AN118 on inverter (and Schmitt) oscillators. They give about 50% duty cycle and can be controlled with a single pot.

  3. tyblu

    Active Member

    Nov 29, 2010
    What is the oscillator and counter for?
  4. redacejr

    Thread Starter Active Member

    Apr 22, 2008
    basically i would like to use it as dc motor speed controller. but then there is a toggle switch that can be set to leave the timer work by itself , or to hook it up to an l293d h-bridge or to a decade timer

    it might not make sens to you but my course is electrical/electronic engeneering , but next semester i will be also having mechanics classes because they really would like to teach us all they can. at the end of this semester they gave me this project which involves electronics , electricity (transformers) , and mechanics , (drilling holes and cutting the faceplate.)

    neext semester i'll be doing a g-clamp from scratch it will be quite a headache.

    we have done all types of triggers and timers and all the rest of the basic stuffs.