Monostable multivibrator problems

MillenniumFalsehood · Post by **MillenniumFalsehood** » Tue Aug 09, 2016 5:02 am

So I'm trying to get a strobe light working using a 556 chip. I have the A side wired up as an astable multivibrator, and it functions just fine if I'm interpreting my meter right (~10v on, 0v off on the output pin, at the correct frequency). The B side of the chip is wired up as a monostable multivibrator, but for some reason the LED that is connected to it is glowing solidly instead of blinking. Any idea what might be causing this?

Component values:

Resistor RA1: 82K
Resistor RA2: 82K
Capacitor CA1: 10uF

Resistor RB1: 12K
Capacitor CB1: 22uF

Sloucher · Post by **Sloucher** » Tue Aug 09, 2016 6:55 am

Can you describe how you've got the pins wired?

In theory, those values should give you a single shot of 0.29 seconds, so I can only guess at a wiring issue? Have you wired reset to Vcc to hold it high until triggered?

MillenniumFalsehood · Wed Aug 10, 2016 12:22 am

The astable side is wired up like this: http://www.circuitstoday.com/wp-content ... brator.jpg

Then the output is connected to the trigger on the monostable side, which is wired like this: http://www.circuitstoday.com/wp-content ... brator.jpg

I've checked the wiring on both sides a hundred times. There are no shorts and the wiring is exactly as done in the diagrams.

Richard Baker · Post by **Richard Baker** » Wed Aug 10, 2016 7:40 am

(sigh)
I really need to get my mind out of the gutter when reading thread titles...

SpaceRanger1 · Post by **SpaceRanger1** » Wed Aug 10, 2016 7:41 pm

Richard Baker wrote:(sigh)
I really need to get my mind out of the gutter when reading thread titles...

Me, too. I had an image of something completely different!

MillenniumFalsehood · Post by **MillenniumFalsehood** » Thu Aug 11, 2016 2:13 am

You two should have been in class the day the teacher introduced us to the monostable and astable multivibrator... Every single person in class was making... inappropriate jokes.

Sloucher · Post by **Sloucher** » Thu Aug 11, 2016 7:42 am

What strobe pattern is it you want to reproduce MF - single flash??

So if its just a single flash strobe you want to produce, then a single 555 could do the job.
R1 = 15k,
R2 = 220k,
C1 = 10uF
and a signal diode (say a 1N4001) across R2 would give you 0.1 sec high (on), 1.5 sec low (off) cycle

As a matter of interest, I made a whole bunch of boards using a 556 to produce both regular nav light flashing from one side and strobe effect from the other. Problem was that 50% of the circuits behaved in much the same way as your circuit does - one half the chip seemed to "lock-up". Not sure why, but it convinced me to use a ATTiny processor instead. Much better control over the flash rates (including double flashing) and other effects as well!

widget · Post by **widget** » Thu Aug 11, 2016 10:48 am

I'm guilty too. I told my daughter she should be ashamed of herself for giving my granddaughters one. Then handed her a toy with blinkie lights and said it was what the circuit was called.
Sorry I can't help with the electronics question.

MillenniumFalsehood · Post by **MillenniumFalsehood** » Thu Aug 11, 2016 3:33 pm

Sloucher wrote:What strobe pattern is it you want to reproduce MF - single flash??

So if its just a single flash strobe you want to produce, then a single 555 could do the job.
R1 = 15k,
R2 = 220k,
C1 = 10uF
and a signal diode (say a 1N4001) across R2 would give you 0.1 sec high (on), 1.5 sec low (off) cycle

As a matter of interest, I made a whole bunch of boards using a 556 to produce both regular nav light flashing from one side and strobe effect from the other. Problem was that 50% of the circuits behaved in much the same way as your circuit does - one half the chip seemed to "lock-up". Not sure why, but it convinced me to use a ATTiny processor instead. Much better control over the flash rates (including double flashing) and other effects as well!

Thanks for values. I think I have all those components other than the signal diode.

Do you have a circuit diagram for how the components are configured? I cared about imitating the precise lengths of how long the flash was versus frequency, hence using both an astable and a monostable to accomplish this (they were the only ones I could find reliable frequency and duration formulas for). But I think at this point I'd rather just call it done and move on to my own projects.

I'd use a programmable chip, but for the fact that I suck at programming at the moment. I'll learn it eventually, but solid state CMOS chips work just fine for the moment for all the special effects I want to do.

Sloucher · Post by **Sloucher** » Thu Aug 11, 2016 5:17 pm

You've already seen the circuit

Its this one:

http://www.circuitstoday.com/wp-content ... brator.jpg

Note the addition of the diode across Rb (shown with a dashed line in that diagram)

There's some useful info here on how to calculate the values you want more accurately:

http://www.doctronics.co.uk/555.htm#astable

Have a look at section 4.1 Extended duty cycle astable

Hope that helps

BTW, learning how to program a microprocessor isn't that bad really. I mean, if I can do it, then it must be simple

They're also small - I produce an effects board that is just 1 3/4" by 1 1/4" that has 8 different programmable outputs and three inputs. It only has 5 components and 3 of those are for voltage regulation!

MillenniumFalsehood · Post by **MillenniumFalsehood** » Thu Aug 11, 2016 8:04 pm

Heheh, yeah, I know... I'm just putting it off because let's face it, laziness is the mother of invention.

I do intend to learn how to program them, though. I have the intention, when I can afford the sheer amount of materials it would cost to build it, to build an AT-AT that is remote controlled and I'll need micro-controllers to coordinate the legs and interpret the sensor data.

I just don't need to now because everything I need to do electronically can be accomplished by an IC and a few discreet components.

Lol, now I understand what you're talking about. XD I think I was just really tired when I asked that... But thanks for the link to that page, though! There's a lot of helpful information there.

Pat Amaral · Post by **Pat Amaral** » Wed Aug 17, 2016 3:05 pm

I learned a huge amount of stuff from this thread
and the links within.

http://www.starshipmodeler.net/talk/vie ... hp?t=62848

It took me just a couple days to figure out everything I
needed.

And the controller boards cost just a few bucks!