Beginner concepts: 555 push button toggle

PIC, AVR, and Arduino are ubiquitous in projects these days and a lot of the time it’s easy to over-complicate things with their use. In this case, [Tod] wanted to use a momentary tactile switch to turn something on and off. Instead of going with a microcontroller he built the circuit around a 555 timer. What he really needed in this case is a flip-flop but lacking a chip for that he went with the 555 because it has one built-in. Three resistors and a capacitor later he’s in business, adding another resistor and a transistor to deal with the load switching. We’ve embedded video of the circuit controlling an LED after the break. This IC ends up in a lot of projects so dig through your parts bin and give this circuit a try.

29 thoughts on “Beginner concepts: 555 push button toggle

  1. I finally purchased one at Rat Shack, and lost it in my friends yard before I even got it home.

    Cool on the use of a flip-flop, I must check that out.

    Maybe eBay has some 555s for a couple $$.

  2. The humble 555 is a handy IC indeed – http://www.kpsec.freeuk.com/555timer.htm features a few of its uses.

    @nubie: I assume it’s because the camera’s sensor doesn’t capture an entire frame at once, but scans from the top down. You sometimes see this on cheap still cameras too (e.g. on mobile phones) in the form of distortion if you move it when it’s capturing data from its sensor.

  3. @Ben Ryves
    Makes me think of the possibility of hacking one of those cameras to create a rudimentary oscilloscope, changing the scan rate to control the sample size. Of course, it would only work with leds, but I think it would still be cool.

  4. If you need *one* 555, it’s still competitive. I was designing a “blinking light with state”… I could have done it with a 556 (2x 555 in one package, use the second one as a flip-flop) but when I costed it out, an AtTiny13a turned out to be cheaper. Fun times.

  5. 555 ICs are among the most versatile chips ever designed. Here’s a very interesting interview with its creator. http://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Index.htm

    Anyway, a toggle button can be built with bare transistors, as some manufacturers did for guitar pedals, flip flops like the cheap 4013 that contains two units into its case so you can build a double switch circuit with it, or microcontrollers.
    I would recommend to the beginners some good books about the 555 and the excellent “CMOS Cookbook” and “TTL Cookbook” by Don Lancaster. They’re fairly old but the principles didn’t change.

  6. There’s a few circuits out there that make it into a nifty frequency generator with relatively low component count too.

  7. no deathventure, he is implying you cant measure pwm with a logic analyzer

    I dont know if you can or not, I havent made one yet but I do know that my 2 channel scope does ok … as long as I dont need to watch more than 2 lines or study them much (small memory space in my 87 kenwood)

  8. Sorry to not note the sarcasm in the statement. A logic analyzer could measure pwm, but it would be a poor and very narrowly focused option, given a 5 volt signal and pwm slow enough for it to recognize, or for somebody to recognize it on a blinking LED. Though the optical analyzer idea is interesting and could work.

  9. nice NotYou, guess I forgot to take into account the enhanced speed of logic analyzers now to the basic ones I’ve used. The optical analysis is still an interesting concept though too.

  10. deathventure: Optical capture would be kinda neat. I looked at CMOS camera modules a few years back and some of them can capture at huge frame rates. Also, a decapped SRAM could be used for capture (since they’re light sensitive) and some of them are very, very fast.

  11. deathventure: Tektronix’s current top-end logic analyzer will handle signals up to 1.4GHz with a timing resolution of 20ps. Agilent probably has comparable equipment.

    Even the venerable HP 1630 is good to 25MHz which ought to be enough for your average PWM…

  12. I agree that an ATtiny would be about as cheap of a solution as a 555 for this application. But the 555 has the advantage of not needing any infrastructure (AVRISP programmer, AVR-GCC cross compiler installed, etc). The 555 can also run directly off a 9V, something most microcontroller can’t do.

  13. dewd: the original problem was that only a momentary switch was available (implemented as a conductive patch on the hoodie’s zipper I think). Some something was needed to go from a momentary contact to an on/off toggle.

  14. I like these programming free hacks. Makes it easy to show beginners really cool things to do. Another aspect of the microcontrollerless prototyping is the lego aspect of it all. Putting your various parts together to make something cool in a single sitting.

  15. @nubie
    @Ben Ryves
    That’s not lens flare :)
    His camera uses a CCD sensor (rather than CMOS). The CCD captures an entire frame at a time, but it does sort of a “bucket brigade” technique to read it out line by line — shifting the charge up a line each iteration.
    Each pixel is basically an integrator for light. That characteristic vertical line is what happens when a few pixels in a column get “too much” charge, the charge gets “smeared” through the entire column as it’s read out. Hence the white line.
    CMOS doesn’t suffer from this, as it uses a different technique for capturing the frame and reading it out.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s