Shop OBEX P1 Docs P2 Docs Learn Events
555 Timer circuit question — Parallax Forums

555 Timer circuit question

eagletalontimeagletalontim Posts: 1,399
in General Discussion
Hello all again! This has to be super simple, but I cannot figure this out for the life of me. I have T8 LED lights in my shed that run from 12V DC and they are/were activated by a motion sensor attached to a simple 555 IC set to keep the lights on for 2 minutes once the motion sensor triggered. That part works, but since I moved the circuit to a soldered project board, the circuit doesn't discharge the capacitor when motion is sensed during the 2 minute count down to keep the lights on for another 2 minutes without turning them off. I built the circuit about 3 years ago on a basic breadboard and it was much too large and sketchy to leave it like that anymore. Maybe there was something different on the breadboard than my new smaller circuit, but I have traced everything I can from the pictures I took before taking it down.

How can I reset the capacitor charge upon trigger without resetting the output of the 555. Basically, if the output is low and trigger brought low, flip output to high and begin charging cap. If trigger is brought low at any point while capacitor is charging, leave output high, but discharge capacitor to reset time. I can post a schematic of needed. Any help is greatly appreciated :)

Comments

  • Francis BauerFrancis Bauer Posts: 364
    Assuming that you did transfer the original breadboard circuit to the PCB, the main difference could be extra amount of capacitance between pins on the 555 Timer when the circuit is on the breadboard vs the PCB.

    Please post the schematic, to see if we can spot anything obvious...

    Are you using the same 555 Timer IC type/package or a different one between the breadboard and the PCB version?
  • eagletalontimeagletalontim Posts: 1,399
    Here is the schematic of the board apart from not using the Opamp, Trigger being pulled high with 10K resistor, R2 being a 100K 1/4W resistor, and the charge capacitor being a 25V 1000uF cap.
    FB_IMG_1605710472977.jpg
    1080 x 615 - 48K
  • eagletalontimeagletalontim Posts: 1,399
    I was using the exact same components as what was on the project board, but I accidentally killed the 555 timer with reverse polarity, so I popped out the old IC from the socket and put in a new one. I believe it is a different brand from the original one.
  • eagletalontimeagletalontim Posts: 1,399
    I just added a diode between Trigger and Discharge and it worked as needed :) No excessive amperage draw according to DCPS so I believe I figured it out.
  • Francis BauerFrancis Bauer Posts: 364
    eagletalontim wrote: »
    I just added a diode between Trigger and Discharge and it worked as needed :) No excessive amperage draw according to DCPS so I believe I figured it out.

    Yes, the addition of the diode should accomplish what you want to do. You will probably need to re-adjust R2 slightly to get back to the 2 minute time delay amount that you want.

    Good job.
  • fengfeng Posts: 39
    http://en.f-alpha.net/electronics/integrated-circuits/timer-555/go-on/experiment-13-retriggerable-monoflop/

    Make R2 a combination of resistor and potentiometer in series.
    In your drawing the discharge pin will try to dicharge the 12V supply with the potentiometer in bottom end position. Nogod.
  • eagletalontimeagletalontim Posts: 1,399
    Timing didn't need to be exact since it is just for shop lights, but it stays on for 1 minute 55 seconds which is good enough for me :) After a trigger event, it stays on for 1 minute 48 seconds which still works well enough.
  • ercoerco Posts: 20,256
    Hey eagletalontim: Glad you sorted out your issue. I'm also a 555 fanboy, I still get a kick out of using this 50-year old IC at every opportunity. Just used two in a project this month. IIRC it was the first IC I ever used way back when, maybe other than an op-amp. There was a metronome project in Popular Electronics and it worked first time! There was initially resistance to using these "black boxes" (ICs) when they first came out. Terms like "shortcut" and "cheating" were often used...

    I still thumb through my Radio Shack/Forest Mims "Engineers Notebooks" occasionally, and my go-to site for 555 info is at https://electronicsclub.info/555timer.htm

    With 200mA output and a bulk price of 4 cents each, I still see these chips being useful for many decades to come.

    https://www.ebay.com/itm/311521048962
  • JonnyMacJonnyMac Posts: 9,102
    I was one of a couple employees with electronics experience at a cyber security company. As the company was all about cross-training, one day my boss non-clamantly said, "Hey, JonnyMac, why don't you get kits for everyone and teach them the 555." Two years ago next week, the day before Thanksgiving, I conducted a half-day class on the inner workings of the ubiquitous 555 and got everyone up and running with blinking LEDs. Some of the hardcore IT types were a bit shell shocked, but all were smiling that they could turn a potentiometer and change the blink rate.

    Sadly, we did our jobs too well and the mayor of LA killed our company, and any chances of its survival. When the courts are back to normal businesses, several lawsuits will expose [even more of] the corruption inside LA city hall. Interestingly, the agency where we discovered some very serious IT problems is an agency that the mayor uses as a cudgel against citizens.
  • kwinnkwinn Posts: 8,697
    @ erco,& JonnyMac, you're not alone in being a fan of the 555. It's amazing how such a simple IC can be used for so many functions.
    Oscillator/clock generator, timer, missing pulse detector, thermostat, level sensor, pwm, etc.. The list goes on and on.
  • JonnyMacJonnyMac Posts: 9,102
    A friend of mine in England -- who received the OBE -- often uses them as watchdogs in microcontroller circuits. If the code doesn't reset the 555 when it supposed to, it will get rebooted.
  • kwinnkwinn Posts: 8,697
    JonnyMac wrote: »
    A friend of mine in England -- who received the OBE -- often uses them as watchdogs in microcontroller circuits. If the code doesn't reset the 555 when it supposed to, it will get rebooted.

    Receiving an OBE is quite an honor. Do you know if it was that for a technical or some other accomplishment?

    Using a 555 as a watchdog timer/missing pulse detector is an excellent use for many applications. I have used it for computers, microcontrollers, and old hard wired logic controllers. My first and most critical use was to protect mass spectrometers from a fore pump failure. If the mechanical fore pump failed the diffusion pump could overheat and cause damage that would cost tens of thousands of dollars to repair.
  • JonnyMacJonnyMac Posts: 9,102
    Receiving an OBE is quite an honor. Do you know if it was that for a technical or some other accomplishment?
    For his work as an engineer.
  • DigitalBobDigitalBob Posts: 1,513
    Corruption in LA, how could this be, who would of thought.
  • frank freedmanfrank freedman Posts: 1,983
    A day without corruption would be like a day without politicians.
  • kwinnkwinn Posts: 8,697
    I am assuming that I am misinterpreting the two prior posts, otherwise I would post something that would probably get me banned from this forum.
  • Francis BauerFrancis Bauer Posts: 364
    You can have a lot of fun with the 555 Timer.

    Back in 2011 I entered a 555 Contest with a Music Box player design that used a number of 555 oscillator circuits using a custom infrared LED paper tape/strip reader. I didn't win anything but I at least got an honorable mention. The following links contain a video and documentation of my project entry:

    Video of the 555 MusicBox playing
    Project/Circuit Documentation
    MusicBoxPlayerBreadboard800x600.jpg
    800 x 567 - 323K
  • kwinnkwinn Posts: 8,697
    Francis Bauer wrote: »
    You can have a lot of fun with the 555 Timer.

    Back in 2011 I entered a 555 Contest with a Music Box player design that used a number of 555 oscillator circuits using a custom infrared LED paper tape/strip reader. I didn't win anything but I at least got an honorable mention. The following links contain a video and documentation of my project entry:

    Video of the 555 MusicBox playing
    Project/Circuit Documentation

    Nice project, and one of my favorite tunes. One of my nieces took up piano and that was one of the first tunes she learned to play. Recently my granddaughter also took up piano and has learned Music Box Dancer as well. There is hope for some musical talent in the family.
  • ercoerco Posts: 20,256
    Fabulous, Francis! Please Youtube that!

    Related and timely: https://www.servomagazine.com/magazine/article/the-biggest-and-smallest-555-youll-ever-see

    555.jpg
    555.jpg
    800 x 911 - 128K
    555.jpg 127.6K
  • MicksterMickster Posts: 2,693
    Before I resort to Google, does anyone have a favorite/proven WD design kicking around?
    I was considering a Picaxe for this purpose. :smile:
  • MicksterMickster Posts: 2,693
    Thinking about it; the Picaxe-08M2 makes more sense for my needs.
  • ercoerco Posts: 20,256
    I use Picaxes. Horses for courses, whatever works. The project I mentioned earlier just needed some pushbuttons to toggle some LEDs on & off. I was about to reach for an 08M2 but I'm glad I Googled a bit and found several sites and videos showing 555 circuits & explanations, as below. Worked great! I see every 555 circuit as a win and another tribute to Hans Camenzind (1934-2012), who designed the 555 [and 565, 566 & 567 (coincidentally the best Corvair years)]. :) I've also used a bunch of 567s in my heyday.

  • Peter JakackiPeter Jakacki Posts: 10,193
    I use the EFM8UB3 for USB serial and reset control on the P2D2 and also as a watchdog via the I2C bus. I also use it for A/D and EEPROM emulation etc, in a tiny 3mm peck all for a buck. It can be programmed over USB.
Sign In or Register to comment.