555 timer 110313

Discussion in 'The Projects Forum' started by allenpitts, Mar 13, 2011.

  1. allenpitts

    Thread Starter Active Member

    Feb 26, 2011
    Hello All About,

    Working ten LED sequencer circuit with no luck. Started to troubleshoot and realized I know little about the 555 IC used in the ten LED sequencer circuit. So backed up and started studying the 555.

    Working on circuit at
    Started building my version
    But I realized that I really don't know what the blue colored object is in
    I surmised it must be the potentiometer since that is the only thing
    not showing in the illustration and the only thing I don't recognize.
    There seems to be a ground rail side of the pot connected by the jumper between 1E and 1F. There is laso a jumper from the pot (3I to 8I) to another jumper (E8 to F8) that connects to two jumpers to the trigger and the threshold of the 555. I see the jumper bewteen J6 and the positive rail on the right. But since a pot is a resistor I am not sure how it can have three separate connectors.


    Allen Pitts, Dallas Texas
  2. wayneh


    Sep 9, 2010
  3. nerdegutta


    Dec 15, 2009
    Just wait 'till Bill_M sees this... :)

    In the mean time:
    The pot in the illustration has the middle pin connected to the 555 pin 6 and pin 2. Can not see that if you have that from the picture.
  4. Wendy


    Mar 24, 2008
    I sensed a disturbance in the farce.

    Why are you wanting to build a Schmitt Trigger bro?

    That particular article was the starter for the series, to demonstrate how a Schmitt Trigger works. There are many 555 configurations that use it, enough that my standard set of templates have that configuration.

    The 555 Hysteretic Oscillator uses the Schmitt Trigger, but for an oscillator, which is probably what you are after.

    BTW, if you need recommendations as to parts, you and I are both lucky Dallas has multiple electronic component retails, world class no less. I can refer you to where to get parts much more than most.
    Last edited: Mar 14, 2011
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    To clear up a slight error in http://www.allenpitts.com/electronics/555/tim42.gif , the passive state of the 555 is pin 2 high & pin 6 is low via R1 & R2. to trigger, momentary ground pin2, pin 3 goes high untill pin 6 is pulled high, resetting 555. There is no timing except by the switches with out a capacitor. Push button switches are available in NO, normally open. or NC, normallc closed, or, form C which has both NO & NC, also with center Off, spring loaded in both directions or just one sided. Probably missed some.
    Last edited: Mar 15, 2011

    AAC Fanatic!

    Jul 1, 2008
    I must say that I've been using the 555 for many years. Bill has managed to document some of the most unique uses for the 555 that they make me feel like a novice user! Just so his head doesn't swell beyond the capacity of his shoulders.... Bill, you didn't include a plot for the 555 Schmitt Trigger tutorial. ;)
  7. Wendy


    Mar 24, 2008
    I've been burned out lately, most of it was that dern flu that left me lower than usual. I'd comment on some of my current projects, but I don't want to hijack this thread.

    I'm not sure where the OP wants to go. It is unusual to have someone within easy driving distance on this forum. If I can help I'll be there, otherwise I check in now and again to see what I can do to help.

    When I make a protoboard I've drawn it looks pretty close to the drawing. I like the wires to lay flat on the protoboard. From what I've seen with other peoples pictures this is rare. It does cut down on the parasitics somewhat, which is always a problem using the protoboards for anything remotely high frequency.

    I'm still trying to figure out how the bistable 555 fits in. I'm always open to suggestions and ideas for 555 projects.
  8. allenpitts

    Thread Starter Active Member

    Feb 26, 2011
    Good morning All About,
    Working with LED sequencers. Built circuit from Chaney 4431 kit:
    which is very similar to
    After the circuit worked I set it in a display. Trying to get it to
    work when someone passes by. So I purchased a passive infrared detector (PID)
    Its a good product and relatively inexpensive at about $15.
    I found a hack sheet which showed me where to solder a couple of wires
    into the PID to output 5 volts to activate a device.
    Connected the PID to the sequencer circuit and got that to work
    The only problem is the output from the PID only lasts two seconds.
    Would like for the sequencer to stay on for a minute or two so the display
    can be seen. In fact the writer of the hack sheet anticipated the longer
    'alarm on' time requirement and supplied a circuit (Figure 3 on the PDF)
    to do just that. But I didn't have those parts so I figured a simple
    555 timer circuit configured in monostable mode would do the trick.
    So I breadboarded a timer circuit
    When I took the positive out put from the PID and connected it to
    pin 2 of the 555 IC the LED indicator came on but it stays on
    until I connect the Reset pin to ground.
    So I went back to the drawing board and researched and found
    where a monstable 555 is used to sound a buzzer for eight seconds.
    But to operate another cicuit the author of 5554.htm added additonal circuitry
    which operates a relay to activate the second circuit.
    Is this what I am missing?
    What kind device is the one in the 5554.htm marked "Second Circuit'?
    For low voltage DC does not a transistor provide the same funcxtion as a relay?
    Is this the type of relay shown in 5554.htm?


    Allen in Dallas
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Add a one transistor inverter between PIR & pin 2 -555, 1 MΩ & 120 μF for timing; connect out , pin 3 to 555 osc pin 4.