I know how to solve the problem mathematically. I just want to find out what kind of bulb would make this circuit flash and where to buy it from. I really appreciate your input. I attached the problem.

 

A neon bulb would work if you can get the DC up to 90V.

 

A neon bulb would work if you can get the DC up to 90V.

Yep...I have a relaxation oscillator flashing away every second with a string of ten 9 volt batteries.....it's been going for nearly a year now.
No...there's no practical purpose for this, except it looks cool.

 

How far below the breakover voltage can a typical neon bulb go before it shuts down. The curves I've seen seem to indicate that it will shut down somewhere around 2/3 of the breakover voltage.

 

Yep...I have a relaxation oscillator flashing away every second with a string of ten 9 volt batteries.....it's been going for nearly a year now.
No...there's no practical purpose for this, except it looks cool.

Hi There
Do you have a capacitor connected to it? What size does it have? Which neon bulb do you have connected to it?

 

How far below the breakover voltage can a typical neon bulb go before it shuts down. The curves I've seen seem to indicate that it will shut down somewhere around 2/3 of the breakover voltage.

What curves?

 

What curves?

Google "neon bulb".

 

I looked a little at fluorescent bulbs but didn’t find anything that looked like it would work. Current barricade flashers are almost all LEDs. I had an old one with an incandescent bulb and never saw one that used that circuit.

 

I know how to solve the problem mathematically. I just want to find out what kind of bulb would make this circuit flash and where to buy it from. I really appreciate your input. I attached the problem.

Hello there,

This brings me way back when i was very young and made my first oscillator circuit. It used 2 neon bulbs though so one was on and one was off and they flipped back and forth.

Your circuit is more theoretical than anything else because the cap wont discharge all the way in a real circuit, so you have some license to cheat a little

Yes a neon bulb would probably do this circuit in real life, but you may have to raise the battery voltage a little more.

 

This was one of the first circuits I ever built that involved passive components. Prior to this circuit I messed with switches and fans (as a young boy). The ones I made (of this type) involved mains power - which is a taboo subject here, but I just half wave rectified the AC current and used a resistor and a capacitor and (as in your diagram) the neon bulb across the cap. Every second or so it would flash.

Aside from NOT discussing the AC component (mains) here's how a neon bulb works: There is infinite resistance between the two electrodes until the voltage rises above its rated ignition point. Once it ignites it becomes a conductor and the capacitor discharges through the neon bulb. Once the cap has discharged to the point below the neon's sustain voltage the lamp goes out and the capacitor begins to recharge. As the voltage again reaches the ignition point the bulb again lights up and drains the capacitor.

I made a display for an electronics store that involved several of these circuits. I noticed that when in operation (behind a plastic lens) if I put my finger near the bulb the flash rate dramatically increased. That was due to the presence of static voltages, which raised the voltage internally in the bulb and caused the bulb to think it was closer to its ignition point.

Whether using mains or a battery (of sufficient voltage) be careful. It can sting, burn and potentially and dramatically shorten your lifespan. In plain terms, it can kill. Which is why mains discussions are prohibited. I'm sure a 90 volt battery with 6 mA or more also can cause death. So regardless of your approach, be careful careful careful.

Your initial question is what kind of bulb would be required to make this work. The answer is "Neon" and ONLY Neon. A regular incandescent bulb when not lit has very low resistance and the capacitor will never be able to charge. Not only that but as the filament grew hotter its resistance would go up dramatically as well. So an incandescent bulb won't work. Fluorescent bulbs work because the filament has been heated sufficiently to cause the mercury in the tube to vaporize and create a conductive path for the high voltage (far above mains voltage) to flow from one end of the tube to the other. It's the phosphorous coating inside the tube that glows and gives off light. An otherwise clear tubed fluorescent bulb would only emit ultraviolet light, harmful to the eyes. So a fluorescent bulb would also not work because you're hot heating the mercury to vapor. An LED works on an entirely different principal and also would not work. So the answer is (again) Neon. The only bulb that will do this.

If you want to flash a different type of light then you'll need the appropriate circuit for whatever bulb it is you're using. Keep in mind that fluorescents take a significantly higher voltage. Making one of those flash at a fast rate would be rather difficult. Not impossible, but not easily. An incandescent bulb such as an automobile bulb would either require an electronic timing circuit or one of those old style blinker control modules. A flashing LED would be the second easiest to construct. You can even BUY flashing LED's if you want, but aside from buying one of those, the easiest way to make a flashing light is the neon bulb in parallel with a capacitor, fed from a sufficiently high DC voltage through a resistor, just as your diagram shows.

 

@MrAl I had one that used 10 bulbs, 10 capacitors and 10 resistors. At times they'd flash in conjunction (rarely) and at other times it would strobe just like the flashing lights on a runway approach. Most of the time they just flashed random. How did you build your 2 NE flashing unit?

 

This was one of the first circuits I ever built that involved passive components. Prior to this circuit I messed with switches and fans (as a young boy). The ones I made (of this type) involved mains power - which is a taboo subject here, but I just half wave rectified the AC current and used a resistor and a capacitor and (as in your diagram) the neon bulb across the cap. Every second or so it would flash.

Aside from NOT discussing the AC component (mains) here's how a neon bulb works: There is infinite resistance between the two electrodes until the voltage rises above its rated ignition point. Once it ignites it becomes a conductor and the capacitor discharges through the neon bulb. Once the cap has discharged to the point below the neon's sustain voltage the lamp goes out and the capacitor begins to recharge. As the voltage again reaches the ignition point the bulb again lights up and drains the capacitor.

I made a display for an electronics store that involved several of these circuits. I noticed that when in operation (behind a plastic lens) if I put my finger near the bulb the flash rate dramatically increased. That was due to the presence of static voltages, which raised the voltage internally in the bulb and caused the bulb to think it was closer to its ignition point.

Whether using mains or a battery (of sufficient voltage) be careful. It can sting, burn and potentially and dramatically shorten your lifespan. In plain terms, it can kill. Which is why mains discussions are prohibited. I'm sure a 90 volt battery with 6 mA or more also can cause death. So regardless of your approach, be careful careful careful.

Your initial question is what kind of bulb would be required to make this work. The answer is "Neon" and ONLY Neon. A regular incandescent bulb when not lit has very low resistance and the capacitor will never be able to charge. Not only that but as the filament grew hotter its resistance would go up dramatically as well. So an incandescent bulb won't work. Fluorescent bulbs work because the filament has been heated sufficiently to cause the mercury in the tube to vaporize and create a conductive path for the high voltage (far above mains voltage) to flow from one end of the tube to the other. It's the phosphorous coating inside the tube that glows and gives off light. An otherwise clear tubed fluorescent bulb would only emit ultraviolet light, harmful to the eyes. So a fluorescent bulb would also not work because you're hot heating the mercury to vapor. An LED works on an entirely different principal and also would not work. So the answer is (again) Neon. The only bulb that will do this.

If you want to flash a different type of light then you'll need the appropriate circuit for whatever bulb it is you're using. Keep in mind that fluorescents take a significantly higher voltage. Making one of those flash at a fast rate would be rather difficult. Not impossible, but not easily. An incandescent bulb such as an automobile bulb would either require an electronic timing circuit or one of those old style blinker control modules. A flashing LED would be the second easiest to construct. You can even BUY flashing LED's if you want, but aside from buying one of those, the easiest way to make a flashing light is the neon bulb in parallel with a capacitor, fed from a sufficiently high DC voltage through a resistor, just as your diagram shows.

Neon bulbs do have a little hysteresis. An NE-2 will usually fire at about 60 volts, and will usually extinguish at around 40 or so.

 

An NE-2 will usually fire at about 60 volts, and will usually extinguish at around 40 or so.

Actually, I believe their ignition voltage is 90 volts and typically their extinguishing voltage is 30% of that. So 60 volts and it should just about go completely out. The closer you get to the extinguish voltage the less the tube glows.

Yes, they DO have a hysteresis, which is why they were one popular method for producing a saw tooth wave. I believe some of the early oscilloscopes employed neon to reset the trace time circuit by suddenly and nearly completely draining the capacitor (from ignition to extinguish voltages). This would reset the sweep.

 

A little off the original topic, but when I built my Allied Radio Knight Kit oscilloscope many moons ago, it used a NE-2 to generate a stable voltage reference.

 

@MrAl I had one that used 10 bulbs, 10 capacitors and 10 resistors. At times they'd flash in conjunction (rarely) and at other times it would strobe just like the flashing lights on a runway approach. Most of the time they just flashed random. How did you build your 2 NE flashing unit?

Hi,

Geeze, i cant remember back that far. I remember a couple caps and resistors and two neon bulbs and i think powered with the line voltage rectified with a selenium rectifier
That was still back in the days of tubes and transistors were just getting out to be popular, maybe even just around just before they came out (aka around early 1960's). We still had tube TV sets back then.

I should have kept it just to remember ha ha. If i had to guess i would say they were cross coupled somehow because only one fired at a time.

As to the hysteresis in the other posts, yes the neon bulbs have hysteresis and that's part of what makes these oscillators work. The circuit being talked about is more theoretical though because it is assuming that the hysteresis is something like 80 volts, where it turns on at 80 volts and turns off at 0v, but really it will turn off much before 0v. I cant remember the spec though but im sure others will or can look it up. This problem though is assuming it turns off at exactly 0v though so we have to follow that.

 

Are we all conceding that no other type of bulb could work with this circuit?

 

Are we all conceding that no other type of bulb could work with this circuit?

I believe so.