@BT25 – We have an Acura MDX with 292,000 miles and still kicking. Older Japanese cars were built to a different standard....

And yes, Cole, if you have the funds saved up and really, truly want this, then go ahead and get it. Of course, if it's not what it seems, then walk away and don't buy on emotion. But otherwise, go for it!

I am interested in one more question :

Assuming the interest is to make it last on a battery as long as possible, changing the flashing from 50% duty cycle to 5..10% is obvious way to extend the battery life. (With 555 this requires additional resistor and diode, as the duty cycle is reverse to what is achievable with the discharge pin. I would drive the capacitor from the 555 main output. With the 2 bipolar multivibrator i guess it can be done just by using assymetrical capacitors ?)

Is there any additional visual brightness benefit (that could be turned into energy saving), if within the on period, the LED strobes at some visible (few Hz) frequency instead of steady on, like using a 2nd 555 ? Instinctively i'd think yes, if only for the facts that it allows to still have some length to the "on" period while actually further cutting down the duty cycle, and that the extra flicker may help catch the eye more for the same average brightness

@Medved
That makes sense, thanks so much for explaining!

This kind of mess always absorbs the shorter wavelengths more than the longer, it absorbs the green too, but less than the blue and UV.
It is the same reason why a duststorm makes the sky yellowish brown.
The difference in MV is, the arc originally does not generate that much of red (to form the brown), but the red is created mainly in the phosphor from the UV.
So with the gradual onset of blackening, the lamp turns into higher CCT first when only the UV is mostly affected. Only later, when the darkening really progresses so it significantly reduces blue as well, the lamp turns green...

@Medved

A symmetrical multivibrator you pictured does not have problems starting even using silicon transistors. In practice, RC constants of base networks will always be slightly asymmetrical, enabling the circuit to start.

It is not that the circuit would stubborny refuse to start when powered ON, it is just not reliable, it requires sufficiently fast turn ON on the supply. And the reliability gets worse once the capacitors ESR increases or if the transistors have higher internal series base resistance (like most high beta transistors do, mainly important at higher currents) and/or the supply has no other source of noise/disturbance on it (sufficient fast ripple on the supply can restart the circuit from the deadlock, but then speeds up the oscillation)
It has nothing to do with symmetry. Try to ramp up the supply slowly, mainly with LEDs as the loads, and you get both transistors steady ON, whatever assymetry you have.
This circuit worked reliable with tubes, because even at the "both ON state" (with grids forward biased and anode voltages low) they had some gain greater than unity, so the circuit started to oscillate. But with silicon transistors featuring hard saturation the transistors lose all voltage gain, so no oscillation start.
Normally when trying it, you start with both capacitors at zero voltage, so when the power supply appears suddenly (rampup faster than time constants) the discharged capacitors do make a kind of bistable flip-flop with it which does select one state (which one depends on symmetry or random noise), where once one transistor becomes off for at least a brief moment kick starts the circuit.
But some brownout, or the supply not rising fast enough and the circuit stays in that "both ON" deadlock.

By the way there is a remedy for it: Do not tie the top end of the base resistors to the supply, but to a separate point, fed from collectors by two diodes. In that configuration when both transistors tend to go on at the same time, the top side of the base resistors loses power, so keeps transistors away from saturation. In that state they have plenty of gain, so the positive feedback via the capacitors amplifies the noise so much it starts to oscillate.
And once running, the top of those resistors get fed from the supply voltage present at the collector of the transistor that is at that moment off (neglecting the voltage drop across the liad). Because they alternate, the bases get supply all the time, so the thing keeps running normally.
But with these diodes we are not talking about the basic circuit anymore...

There are many places where the skill bar is rising, in some places in ways which are clearly not for the benefit of anyone who wants to mess with the technology. This in itself can be a whole discussion

I would not lump SMD as a whole in there, and definitely not lump all of SMD into one "thing". Indeed, it is not through hole, but in 99% of the components i might use in a design, i get to choose the component size to my liking within what's available

Check out the following component sizes and see if thy are ok for you :

 - ICs : SO and SOIC packages, 0.05" pin pitch. For 16+ pin ICs a "wide body" option is often available. DIP adapters are available to plug those into breadboards as through hole components

 - Transistors : TO-261 (SOT223), TO-252 (DPak), TO-263 (D2Pak). Those are generally packages of higher power transistors, but in many cases they can be used for small signal stuff without issues (just being overkill in size and cost), at least as long as you have 5V+ supply available to drive larger MOSFETs sufficiently for small signal work

 - Small transistors : TO-243 (SOT89), SOT23

 - Diodes : DO214 (3 sizes : SMA SMB SMC), SOD123

 - Resistors and capacitors : 1206 and larger (2010, 2512)

My own preference for components : TSSOP/MSOP generally ok, (SO/SOIC for 8 pin chips, SO wide-body for 16+ pin chips if i want to trade space for making it easier to assemble), SOT23 (SOT323 and SOT363 in a pinch), SOT23-5 (some small chips), SOD323, 0805 (0603 if i want to save space, which i usually do)

That is what i can do with just an iron, without much effort, and without needing the magnifier (though i do have a few circline magnifiers and a microscope). I can do some higher level stuff, but dont want to, and i avoid it from things i design. I consider my SMD skill as medium-low to medium



The type of iron you use will absolutely determine your soldering experience

The entry level for anything more than TH components on single sided PCBs is a closed loop temperature controlled iron, such as most entry level "stations" (including the many Chinese clones of old Hakkos)

(Admitting, i have successfully got away with 25W "just soldering iron" and 30/120W "two level handgun" irons through most of my life as a younger kid, but keep that to "in a pinch" situations nowadays)

The next level, good for easy SMD jobs, is an iron with improved heat conduction. Those are the newer ones with element built into the tip, rather than a ceramic element with screw-on tip as most older "stations"

The further next level is an iron with heat generation at the tip itself. Those are induction irons. Here i am now with an old Metcal SP200 and 1.5mm flat tip



Nothing beats Through Hole, and many things can be done with Through Hole at the level you are now exploring. This circuit is no exception, the CMOS 555's and the suggested transistors i provided are all Through Hole. (You may find better ones in SMD, but those will work)

And if you have to use some component which is SMD, you still can switch only this one component to SMD in a Through Hole circuit



I have not suggested the bipolar-based entire circuit route. My suggestion remains with CMOS 555 and a suitable output transistor, with the following options :

 - Use a MOSFET which will work at the 3.x V drive current and handle your load. Not all MOSFETs will have low RDS at such voltage, but the good part is, the MOSFET's resistance will just behave as another series resistor with the LED. It will self regulate to a point where the LED can still work with the provided voltage, even if a little dimmer. At such small loads and with the MOSFET being otherwise adequate for the current and power dissipation, you are unlikely to run into SOA problems

 - Use any MOSFET + a charge pump driving circuit (requires extra 1 capacitor, 1 resistor and 1 diode). This will open your choice to a wide range of MOSFETs with good RDS and current ratings, but it will be absolutely essential that the pump keeps "pumping" (ie. that the 555 keeps flashing the LED, and not just stay on), or else your circuit will drop into the twilight zone of insufficient MOSFET driving

 - Use a bipolar transistor. This can be easily driven by the 555, but requires non-zero driving current (generally not an issue) and drops a fairly fixed voltage even at low currents, limiting the voltage headroom for the LED

A reality of today is many interesting components are available in SMD only. Why stick with 60 years old 2N3904s when you have nice modern AO3400 MOSFETs switching 5A at 30V with zero current at the gate and minor dissipated power? Soldering SOT23 (and 0805 -1206 passives) is not that complicated, as actual pin pitch is about the same as plastic through hole TO92 case mentioned. For success, you need a temperature controlled soldering iron set to ~320C, with say, 1.5mm flat screwdriver blade tip, some 0.8mm lead solder, and some gel flux. All very inexpensive. Keep the tip clear with a wet sponge, and keep it completely tinned all the time, this is important. Apply an excess of flux, surface tension will really do the rest for you

Some prefer to use a soldering paste, no problem, you put some blobs of paste out of a syringe on the board contacts, apply components and reflow with air source of ~350C, heat gun or electronics air tool. No absolute need for a reflow oven.

While I do not disagree with you on the fact that a lot of newer chips are only available in SMD, And I don't disagree that it is not technically complicated. I just don't wish to use SMD for essentially blinken an LED. especially when I have a LARGE supply of THT components either in bins or on scrap PCBs. I have ZERO SMD components aside from high powered LEDs. ironically the 3 watt LEDs i Soldered are SMD lol. and those are really big and I still shock around like a MF trying to set them up and center them with tweezers. I don't know if I have a vitamine defficiency or what. I would be a terrible TIG welder thats for sure 


anyway I have like a billion through hole transistors kicking around. and a bazillion resistors. I have a capacitor shortage but I still have enough to make it blink in some sortof way.

Check out this cool looking old forklift battery charger PCB with this weird number selector switch on it, resistor networks, a cool little self contained screen with controller chip integrated and old skool TO-92 transistors with heat sinks on top. one of my many scrap PCBs lol. I do wonder if that socketed chip is a ROM or if it re writable.

Ah, were you ever able to order one from cooper or somebody? Or just everybody was already out of hid?

@Medved

A symmetrical multivibrator you pictured does not have problems starting even using silicon transistors. In practice, RC constants of base networks will always be slightly asymmetrical, enabling the circuit to start.

A reality of today is many interesting components are available in SMD only. Why stick with 60 years old 2N3904s when you have nice modern AO3400 MOSFETs switching 5A at 30V with zero current at the gate and minor dissipated power? Soldering SOT23 (and 0805 -1206 passives) is not that complicated, as actual pin pitch is about the same as plastic through hole TO92 case mentioned. For success, you need a temperature controlled soldering iron set to ~320C, with say, 1.5mm flat screwdriver blade tip, some 0.8mm lead solder, and some gel flux. All very inexpensive. Keep the tip clear with a wet sponge, and keep it completely tinned all the time, this is important. Apply an excess of flux, surface tension will really do the rest for you

Some prefer to use a soldering paste, no problem, you put some blobs of paste out of a syringe on the board contacts, apply components and reflow with air source of ~350C, heat gun or electronics air tool. No absolute need for a reflow oven.