# 1.5 volt bulb won't light in my circuit newbie

Oct 5, 2014
7,053
Last edited:

May 10, 2019
116

#### BobK

Jan 5, 2010
7,682
If you are going to use a DC to DC conveter, it would be best to get one with a current limit. Then you set the current limit and no resistor is needed.

Bob

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,891
Curious if I understand this video correctly
In my circuit , if I put 3 of my 1.5 volt bulbs in series, I could then use a smaller resistor right?
Yes, you could, but you are missing the whole point of the video. You don't need, and should not use, resistors to set the current passed through one, two, three... or however many... LEDs!

That you used resistors in the beginning was so you could learn about how LEDs work, how much voltage they require to "light up" and how to use resistors in simple way to set the current drawn by the LED or LEDs (if more than one). All that is still valid and was a necessary part of your learning experience with LEDs, but it is time to move on to more efficient ways. Along the way, don't forget to visit LEDs of different colors, which all have different operating voltages that depend on their color. Red (and infra-red) is the lowest voltage and the voltage increases as the color moves though yellow, orange, green, blue, and ultra-violet. So-called white LEDs are actually ultra-violet LEDs illuminating a phosphorescent light emitter, reminiscent of fluorescent lighting.

Unlike your 1.5 V incandescent lamp, which requires a fixed (constant) voltage to operate properly, your LED requires a fixed (constant) current. Power, as received at the convenience outlets in your house or as delivered from a battery, is provided at a fixed (constant) voltage. It requires a bit of circuitry and solid-state (semiconductor) components to efficiently deliver power to your LEDs at a fixed (constant) current. Thankfully, it is now quite inexpensive as well as efficient to do just that!

You will notice that the circuit board in the video you posted has a LOT of probably unfamiliar components. Never mind that! The engineering and product testing has already been done for you. Just purchase the module and connect four wires (plug and chug) for around a buck American or thereabouts. Voila! You will now have an adjustable, constant-current, power source for all your LED experiments. As a bonus, most of these modules can also be adjusted to operate as adjustable constant-voltage power sources, which you will eventually need for experiments as you continue your journey into the fascinating world of hobby electronics.

Others here have mentioned the impracticality of using tiny 9V "smoke alarm" batteries for your experiments. Batteries, even if you use rechargeable ones, are expensive and have limited power availability and energy storage capability. However, to gain better operating life, you should purchase a battery cell holder for six size-D dry cells and wire the cells in series. Most battery holders are already wired with the cells in series, but check to make sure. This arrangement will provide an initial output of 9 VDC with at least one ampere of current capability. It should be more than enough until you venture into the area of power electronics with motors and high-wattage audio amplifiers.

For serious experimentation I cannot over-emphasize the need to employ the full faith and credit of your local electric utility to power up a "wall wart" capable of delivering at least nine volts at a few hundred milliamperes of current. Avoid so-called 5V USB wall wart cell-phone chargers because some of them can be quite dangerous. A real wall wart power supply has a substantial "heft" to it because it incorporates a transformer to isolate the power supply output from the power line of your public utility. This transformer may not necessarily be used at 60/50 Hz power line frequencies, but may instead operate at a much higher frequency as the power line is rectified to DC, the DC used to power an oscillator, and the oscillator used (with a high-frequency transformer) to deliver isolated power to the wall wart output. Again, all at a very inexpensive cost and high efficiency.

#### Bluejets

Oct 5, 2014
7,053
If you are going to use a DC to DC conveter, it would be best to get one with a current limit. Then you set the current limit and no resistor is needed.

Bob
That's what is in the video. It is both voltage and current adjustable. (V and I markings on the 2 pots)

#### BobK

Jan 5, 2010
7,682
But that is not what the TS git out of it. He said he could use a smaller resistor.

Bob

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,891
@stspringer is perhaps now stuck in a loop, where he believes a current-limiting resistor is both sufficient and necessary to control the LED current. As Bob, Bluejets, and I have been trying to explain, a resistor may be sufficient but it it is never necessary to control the LED current, just as long as the LED is driven from a constant-current module.

No further progress can be made until he gets past this hurdle. So, someone might as well close this thread so we can all move on to something mo' betta or mo' entristing, at least until adequate understanding is demonstrated... <sigh> Maybe we are piss-poor teachers, or maybe it's just me who fails to get the concept across...

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,769
So, someone might as well close this thread so we can all move on to something mo' betta or mo' entristing, at least until adequate understanding is demonstrated.
Closing the thread will not advance the op's understanding - plus it will dissalow any more requests to be added to this thread. Therefore I think we will not close this thread.
Maybe we are piss-poor teachers, or maybe it's just me who fails to get the concept across...
Patience is of the essence here. I'm sure we'll be able to sort things out. We've come a long way from the first post in this thread.

Our ressource Got a question about driving LEDs? is a good entry point for understanding LEDs and their drive requirements.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,891
Patience is of the essence here. I'm sure we'll be able to sort things out. We've come a long way from the first post in this thread.
Harald, you are right of course. It does no harm to see what happens next, and perhaps things will sort themselves out. Meanwhile, I have a comment on an earlier comment @stspringer made...

I am just a hobbyist, and a gadget man, and enjoy learning new things.
That's a pretty good attitude. Many of us here began careers in electronics or electrical work as hobbyists. And most Americans love their gadgets. The joy of learning new things is an often undiscovered pleasure that can be the result of a decent education. OTOH, I have met people (fellow students) who cannot understand why anyone would want to learn any new thing that was not mandatory... it seems learning is actually painful for such folks. Consider yourself blessed.

#### Bluejets

Oct 5, 2014
7,053
Along the same lines, friend of mine and I are also into model engineering.
I do his ignition systems, he helps with my castings.

He often talks about how, when he was a kid, he would stare into the window of a local hobby shop in the UK where he lived then and think, yeah, one day.

Later he became a tech teacher at high schools.

Couple of weeks back, took one of his creations on a trip from Aus to the UK and won the most prestigious "Duke of Edinburgh" award for model engineering.

#### CharlesMc

Jun 6, 2019
1
A lot of stuff was discussed here and I imagine some of it was way over your head. It appears your goal is to learn ohms law through experimentation. What are you using for training material?
I know a couple of books that are excellent resources for a beginner.
1. Lessons in Electric Circuits, vol 1: https://www.ibiblio.org/kuphaldt/electricCircuits/
2. Navy Electricity and Electronics Training Series Mod 1: https://www.fcctests.com/neets/Neets.htm
Both are really good and will give you more detail than most online tutorials.
It has a large learning curve but when you have a lot of calculations to do it allows you to experiment. You can set up multiple equations and experiment with the values. A change of any value triggers a recalculation of all the equations. Much easier than going through multiple calculations on a calculator.

#### stspringer

May 10, 2019
116
A lot of stuff was discussed here and I imagine some of it was way over your head. It appears your goal is to learn ohms law through experimentation. What are you using for training material?
I know a couple of books that are excellent resources for a beginner.
1. Lessons in Electric Circuits, vol 1: https://www.ibiblio.org/kuphaldt/electricCircuits/
2. Navy Electricity and Electronics Training Series Mod 1: https://www.fcctests.com/neets/Neets.htm
Both are really good and will give you more detail than most online tutorials.
It has a large learning curve but when you have a lot of calculations to do it allows you to experiment. You can set up multiple equations and experiment with the values. A change of any value triggers a recalculation of all the equations. Much easier than going through multiple calculations on a calculator.

#### stspringer

May 10, 2019
116
Yes, you could, but you are missing the whole point of the video. You don't need, and should not use, resistors to set the current passed through one, two, three... or however many... LEDs!

That you used resistors in the beginning was so you could learn about how LEDs work, how much voltage they require to "light up" and how to use resistors in simple way to set the current drawn by the LED or LEDs (if more than one). All that is still valid and was a necessary part of your learning experience with LEDs, but it is time to move on to more efficient ways. Along the way, don't forget to visit LEDs of different colors, which all have different operating voltages that depend on their color. Red (and infra-red) is the lowest voltage and the voltage increases as the color moves though yellow, orange, green, blue, and ultra-violet. So-called white LEDs are actually ultra-violet LEDs illuminating a phosphorescent light emitter, reminiscent of fluorescent lighting.

Unlike your 1.5 V incandescent lamp, which requires a fixed (constant) voltage to operate properly, your LED requires a fixed (constant) current. Power, as received at the convenience outlets in your house or as delivered from a battery, is provided at a fixed (constant) voltage. It requires a bit of circuitry and solid-state (semiconductor) components to efficiently deliver power to your LEDs at a fixed (constant) current. Thankfully, it is now quite inexpensive as well as efficient to do just that!

You will notice that the circuit board in the video you posted has a LOT of probably unfamiliar components. Never mind that! The engineering and product testing has already been done for you. Just purchase the module and connect four wires (plug and chug) for around a buck American or thereabouts. Voila! You will now have an adjustable, constant-current, power source for all your LED experiments. As a bonus, most of these modules can also be adjusted to operate as adjustable constant-voltage power sources, which you will eventually need for experiments as you continue your journey into the fascinating world of hobby electronics.

Others here have mentioned the impracticality of using tiny 9V "smoke alarm" batteries for your experiments. Batteries, even if you use rechargeable ones, are expensive and have limited power availability and energy storage capability. However, to gain better operating life, you should purchase a battery cell holder for six size-D dry cells and wire the cells in series. Most battery holders are already wired with the cells in series, but check to make sure. This arrangement will provide an initial output of 9 VDC with at least one ampere of current capability. It should be more than enough until you venture into the area of power electronics with motors and high-wattage audio amplifiers.

For serious experimentation I cannot over-emphasize the need to employ the full faith and credit of your local electric utility to power up a "wall wart" capable of delivering at least nine volts at a few hundred milliamperes of current. Avoid so-called 5V USB wall wart cell-phone chargers because some of them can be quite dangerous. A real wall wart power supply has a substantial "heft" to it because it incorporates a transformer to isolate the power supply output from the power line of your public utility. This transformer may not necessarily be used at 60/50 Hz power line frequencies, but may instead operate at a much higher frequency as the power line is rectified to DC, the DC used to power an oscillator, and the oscillator used (with a high-frequency transformer) to deliver isolated power to the wall wart output. Again, all at a very inexpensive cost and high efficiency.

Thank you,
Sorry I took so long to reply, I was on vacation. I understand what you are saying now and thank you for all your useful input.

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