Help, I don't have a clue!

[Thornton Davis]

Hi everyone,

I'm hoping that I've come to the right place to get some help.

My daughter has a school project that needs to be completed in a weeks time and she has no mechanical skills at all when it comes to working with soldering irons, working with circuits, etc, so she's asked me to help her out. My mechanical skills are not bad, so I can get by if I know what I'm doing.

Here's the poop. We need to create 2 circuits within a toy. The toy is a plastic dump truck that will have the following components installed in it;

2 x 2.8 V White LED's
4 x 20mA Coloured LED's
2 x Mini toggle switches (1 per circuit)
1 x 9volt battery

These LED's will become two head lights (White LED's) and two safety lights (yellow LED's) mounted on the cab of the truck. These are on circuit A

The two remaining LED's are red and will become tail lights. These are on circuit B

Part "A" of the plan is to have one of the toddle switches turn on the 2 x 2.8 V White LED's + 2 x 20mA yellow LED's on a single circuit. The power source is the 9 volt battery.

Part "B" of the plan is to have the second toggle switch turn on the remaining 2 x 20mA red LED's on a separate circuit. All LED's do not need to be on simultaneously.

I know I'm going to need some resistance in the circuits. I do have some 1k 1/4W 5% CF resisters that I can use, but I don't know how many to use. Also I do have to assume that they must be installed in the circuit between the on/off switch and the first LED. Is that correct? Do I add them right into the circuit with however many are required placed into the positive connection and the equal amount into the negative connection?

What would this look like on paper and how do I do the math to arrive at what is needed resistance wise? Also do I make all my connections straight up with all positive connections being connected to positive and like wise for negative, or do I need to do some fancy footwork? Remember both circuits are separate and will not function at the sametime.

I appreciate any assistance that anyone can give me. I'm not an electronics guy, so please forgive my ignorance. I need this to be as simple as possible.

Thanks very much in advance.

TD

 

[DerStrom8]

Hello, and welcome to Electro-Tech
You are correct in assuming that a resistor should be put in SERIES with the LED (between the battery and the LED). Assuming your 9 volt battery actually puts out 9 volts, and your colored LEDs draw 20mA, then for a resistor (for a single LED) you would need: (V=IR), 9=.02R, R=450 ohm resistor per LED. If you want to use two LEDs in series (which I recommend for the tail lights, etc., You could use a slightly lower value. If you use your 1K resistors, you would have 9=I(1000), I=.009, or 9mA, so the LED wouldn't be as bright, but should still be visible. Again, if you want two LEDs in series, you would almost definitely want a lower value resistor. It would be safe to assume you would need a resistors of about 500 ohms whether you want to put the LEDs in series or parallel.

Not quite sure what you mean by "Do I add them right into the circuit with however many are required placed into the positive connection and the equal amount into the negative connection?" One resistor for each LED (or pair of LEDs, as the case may be) is all that is needed. Simply connect your battery positive terminal to the switch, the other leg of the switch to the resistor, the other end of the resistor to the anode of your LED, and finally the cathode of your LED to ground (negative of the battery). This is a complete circuit and will allow you to switch your LED on and off with your toggle switch.

As for the math you may need, use Ohm's Law (which is what I used earlier--V=IR), where V is the voltage, I is the current in Amps, and R is resistance of your resistor. This is probably all you need for these circuits.

I'm afraid I'll have to let someone else draw the diagram for you, as I am rather busy at the moment. Let me know if you need me to clarify anything, though

Best regards,
Der Strom

 

[MikeMl]

To get two Leds running on 9V, put the two Leds in series (anode of one connected to cathode of the other), then make an assembly of two or three 1K resistors connected in parallel, put that between the positive pole of the battery and the anode of the first Led. Connect the cathode of the second Led back to the negative pole of the battery. You can break the wire to the positive pole of the battery with a toggle switch.

Two 1KΩs in parallel are 500Ω; three are 333Ω.

 

[DerStrom8]

A quick edit on my previous post:

When trying to find the necessary resistance for an LED, you can't just use V=IR. Instead, you have to have Vsupply-Vled=IR. So in your case, with 20mA LEDs, you would need to also find the voltage of your LED as well as the current. To find necessary resistance, subtract the voltage of your LED from the supply (assuming 9 volts), and then divide by the current (.02A) and that leaves you with resistance.

Does this make sense?

Der Strom

 

[Grossel]

Hi. Sorry for dumb question, but what is a "toddle switch"?

I searched on google pictures to get an idea, but google just returned nonsense.

 

[DerStrom8]

Hi. Sorry for dumb question, but what is a "toddle switch"?

I searched on google pictures to get an idea, but google just returned nonsense.

It was just a typo. He actually meant "Toggle switch," which he wrote correctly earlier in the post.

 

[crutschow]

Maybe it's a switch that can be operated by a toddler.

 

[Grossel]

Maybe it's a switch that can be operated by a toddler.

???
So it's probably just a very "nice looking" switch? Safe for children?

 

[Thornton Davis]

Toddle switch?

Yeah, it was my spastic left handed index finger that hit the "d key" twice rather than the intended "g key". My apologies, but it did provide me with a chuckle once you guys noticed it.

Going to have some more questions later today. I'll post them once I make it home.

Thx

TD

 

[Thornton Davis]

Toggle switch connection?

Question!!

I need to connect my circuit to a mini toggle switch so I can turn the circuit for the LCD's on and off. The switch has 3 contact points on the bottom of it, which I'll assume are +, -, and common, which is the center contact.

Do I simply connect the + and - circuit to the + and - on the switch, or do I need to connect one of the lines to the + or - and the other to the common poistion (middle)?

Thx,

TD

 

[DerStrom8]

Question!!

I need to connect my circuit to a mini toggle switch so I can turn the circuit for the LCD's on and off. The switch has 3 contact points on the bottom of it, which I'll assume are +, -, and common, which is the center contact.

Do I simply connect the + and - circuit to the + and - on the switch, or do I need to connect one of the lines to the + or - and the other to the common poistion (middle)?

Thx,

TD

No, the pins are not +, -, and common. I would assume it is more like +, -, +, though this does not actually represent polarity. The - pin (which is common) connects to one side or the other, depending on how it is toggled. To connect your circuit, look at this simple diagram:



The symbol on the far right (what looks like a bunch of "stacked" lines) is the battery. The longest line on the end means the positive side of the battery. The funny-looking symbol on the top right is the switch. The third pin (the second "+") of the switch is not connected. Other than that, it does not matter which of the remaining 2 pins of the switch connects to which part of the circuit. The jagged line is your resistor, and the arrows on the left are your LEDs.
I hope this helps!
Der Strom

 

[Thornton Davis]

Thank you Der Strom. You confirmed my suspisions.

One more question, so I bring my circuit to the LED's which both have a + and - connector. Do I run my + wire from my switch to the + LED connection? Then connect a wire to the - side of that LED which in turn connects to the + connector on the next LED, then connect the - side of that LED back to the toggle switch? Sorry, I don't have a scanner here at work that I can use to create and upload a drawing of this, but I do at home and will do so when I get there tonight.

 

[DerStrom8]

Thank you Der Strom. You confirmed my suspisions.

One more question, so I bring my circuit to the LED's which both have a + and - connector. Do I run my + wire from my switch to the + LED connection? Then connect a wire to the - side of that LED which in turn connects to the + connector on the next LED, then connect the - side of that LED back to the toggle switch? Sorry, I don't have a scanner here at work that I can use to create and upload a drawing of this, but I do at home and will do so when I get there tonight.

First, you must connect the positive (+) terminal of your battery to the middle pin of your toggle switch. Then, connect one of the outer pins to your resistor. Connect the other side of your resistor to the (+) side of your first LED, then connect the (-) side of that LED to the (+) of your second one. Finally, connect the (-) side of your second LED to the negative (-) terminal of your battery. And that should be it! You should now be able to turn your LEDs on and off with the toggle switch.
Der Strom

 

[Thornton Davis]

Gottcha!! Many thanks.

TD

 

[Thornton Davis]

Thanks DerStrom8, the project came together perfectly. I appreciate the help.

TD

 

[DerStrom8]

Thanks DerStrom8, the project came together perfectly. I appreciate the help.

TD

I am very glad to hear of your success! I am always happy to help.