# Circuit with 2 LEDs, 2 AAA Batteries, a potentiometer and a switch

#### Rémy Thijssen

Joined Sep 15, 2018
5
hi AAC Community!

I need some help on a school project at physics : I need to modify some magnifying glasses that have a couple of light bulbs on each side. I need to make a circuit that would have 2 leds (4 in total, basically 2 on each side), 2 switches, 2 potentiometers and they have to be powered by 2 AAA batteries (basically 4 of them, I need the same circuit on one side and the other). the problem is that I can't use a breadboard as I do not have the space required for it, so I need to design a PCB, and I'm a total noob. and I do not know what to actually buy, like what is the value required for the potentiometers and for the leds. can you help me with that, please? I have the deadline until the 3rd of October, I just do not know where to start.

any help would be gladly apreciated, thank you!!

#### Picbuster

Joined Dec 2, 2013
990
start with description, mechanical layout and schematic. ( each side circular, square 1 mm or 10 meter or somewhere in between?)
show us the calculations used to select the components. ( type of led, current, voltage, when to switch on what led)

Do not to expect us to design it for you but you could expect us to produce hits, allowing you to trigger your grey cell's and solve the problem)

Picbuster

#### Rémy Thijssen

Joined Sep 15, 2018
5
start with description, mechanical layout and schematic. ( each side circular, square 1 mm or 10 meter or somewhere in between?)
show us the calculations used to select the components. ( type of led, current, voltage, when to switch on what led)

Do not to expect us to design it for you but you could expect us to produce hits, allowing you to trigger your grey cell's and solve the problem)

Picbuster

I'm not expecting anyone to make anything for me, sorry if you got that wrong. Actually I had kind of omitted the question that I wanted to ask originally when I wrote the thread *lol* I wanted to ask about the values of the components that I need to get, like the wattage of the LEDs and the values of the potentiometers and resistors. I can do the math, but I don't really know how to apply the formulas for both of the batteries. And btw, can you recommend me a good and interactive PCB design program for noobs like me? Thanks again, cheers!

#### dl324

Joined Mar 30, 2015
9,576
Welcome to AAC!
I wanted to ask about the values of the components that I need to get, like the wattage of the LEDs and the values of the potentiometers and resistors.
As this is a physics project and you haven't stated the objective of the project, I want to err on the side of caution and not feed you answers. Google Ohm's Law and Watt's Law.

When using pots, the power dissipation rating is for the entire resistance. If you had a 1k pot and were only using 1/5th of the resistance, power dissipation would need to be reduced to less than 1/5 of the rated value. We seldom operate components at 100% of their maximum rating.
can you recommend me a good and interactive PCB design program for noobs like me?
Check out Kicad or ExpressPCB. I've used ExpressPCB and it was easy to learn how to use. Never used Kicad, but it seems popular. I use the free version of Eagle, but some have said it's too difficult to learn.
I have the deadline until the 3rd of October
That's only about 2 weeks. You may not have time to have boards made commercially. For simple circuits, you could hand draw on copper clad board with an etch resist. Then etch, drill, and assemble.

Just because this is an electronics related site, that doesn't mean we don't care about good grammar.

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#### Rémy Thijssen

Joined Sep 15, 2018
5
As this is a physics project and you haven't stated the objective of the project, I want to err on the side of caution and not feed you answers. Google Ohm's Law and Watt's Law.

When using pots, the power dissipation rating is for the entire resistance. If you had a 1k pot and were only using 1/5th of the resistance, power dissipation needs to be 1/5 of the rated value.
Check out Kicad or ExpressPCB. I've used ExpressPCB and it was easy to learn how to use. Never used Kicad, but it seems popular. I use the free version of Eagle, but some have said it's too difficult to learn.

Just because this is an electronics related site, that doesn't mean we don't care about good grammar.

I see that you guys can be a little rude, English is not my first language. Anyways, I appreciate your answer and thanks for the info!

#### crutschow

Joined Mar 14, 2008
24,076
When using pots, the power dissipation rating is for the entire resistance. If you had a 1k pot and were only using 1/5th of the resistance, power dissipation would need to be reduced to less than 1/5 of the rated value.
Another way to rate the pot is to calculate the current through it for it's power rating and total resistance.
Then never exceed that current.
Thus, for example, the maximum current for a 1W, 1kΩ pot would be, using Watt's law, √(1W/1k) = 31.6mA.
Allowing for a derating of 75%, you should not exceed about 24mA though the pot for any wiper setting.
I see that you guys can be a little rude
Not rude so much as blunt, as engineers are prone to be.

#### Rémy Thijssen

Joined Sep 15, 2018
5
Another way to rate the pot is to calculate the current through it for it's power rating and total resistance.
Then never exceed that current.
Thus, for example, the maximum current for a 1W, 1kΩ pot would be, using Watt's law, √(1W/1k) = 31.6mA.
Allowing for a derating of 75%, you should not exceed about 24mA though the pot for any wiper setting.
thank you very much for taking your time to respond, I appreciate it greatly!
Not rude so much as blunt, as engineers are prone to be.
haha, good to know