normal output voltage for astable multivibrator

Discussion in 'General Electronics Chat' started by robo5050, Jan 20, 2008.

  1. robo5050

    Thread Starter Member

    Dec 6, 2007
    Hello forum members
    I have a new problem that has to do with the output voltage for
    an astable multivibrator based in a CD4011 NAND Gate chip;
    I tested the output voltage of the NAND gate with 12 volts being input to the gate,but the A.C. voltage measurement I got was around 2-3 volt output
    on a generic D.M.M.!!
    I did this test with the following parameters present:220K ohm resistor on the Vss of the Gate,and the astable section of this CD4011 output paralleled into the remaining two gates(4 gate chip) with only manual pressure being applid on the D.M.M.test leads/Voltage supply leads!!

    I would like to know if this is a normal reading for this chip,and if not,what may be the problem other than the 4011 itself(since I did get a voltage reading from the output)???
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    You were probably trying to measure the oscillating output with a DC voltmeter. That will give you a reading that is a value somewhere between the highest voltage and the lowest voltage reached by the signal being measured. The value measured will depend on the duty-cycle of the squarewave and the frequency of the squarewave and the responsiveness of your meter.

    With the meter set to AC you were reading the peak voltage.

  3. robo5050

    Thread Starter Member

    Dec 6, 2007
    I am most positive -no pun intended-that I used the A.C. voltage scale for the output voltage measurement,but might have had too much resistance(battery and discrete current reducing resistor)in the power supply input of the 4011?!?

    BTW,I would upload some pictures of the circuit ,but have problems with there size:217 kbytes that is about 119 k bytes over allaboutcircuits upload size!!
    I would like to know what jpg shrinking software somebody might recommend
    for reducing the file size of my astable circuit scans???
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    I may be misunderstanding you, but you don't need a current-limiting resistor in series with the supply. In fact, the circuit won't work that way.
  5. robo5050

    Thread Starter Member

    Dec 6, 2007
    Hello forum members,
    The 220 kohm resistor I had in the circuit was indeed series-connected(oops!!)from the "+" battery terminal to the NAND gate power supply pin;that
    is probably why my output voltage read so low on my D.M.M.!!

    I will try measuring the output voltage again without the 'droppimg' resistor at the power supply imput to see if that makes a difference!! I know that the voltage measurement on a D.M.M-at least my Centech-only measures the R.M.S. of the pulsed/A.c. signal,but should not read as low as the test with the series resistor installed!!:rolleyes:
  6. robo5050

    Thread Starter Member

    Dec 6, 2007
    I just got done testing the astable without the series-connected resister,and got a reading of 6.9 volts R.M.S.!!
    I think that the resistor was dropping too much voltage for the NAND gate to operate
    Next item I will be working on is the voltage doubler-Cockcroft or Dickson voltage multiplier-
    to get the required voltage of 28-30 volts.