any electronics hobbyists?

[byak]

I'm trying to put together a simple little project with a handful of $1.50 Radioshack components, a battery, and some wire. I've never done anything like this before. The extent of my electronics experience is a physics class.

Any tips for someone new to putting things together? Are there commonly used programs to measure voltage/amperage before you put everything together and figure out you just fried your twelve LEDs and drained your 9V battery in seven seconds? Or is it standard to do all the math and design on paper and figure everything out by hand?

Thanks

 

[HappyPuppy]

Don't lick the wall sockets. I'm sure there will be others with equally good advice.

 

[byak]

Is a 9V safe to lick?

 

[clamum]

Hell yeah. Put your tongue across the two thingies. That way you can test battery strength and all you need is your tongue!

 

[Hayabusa Rider]

What are you trying to make?

 

[FrustratedUser]

So what do you need to do?
Connect a LED to a 9 V battery?

If you need to this is how to:

Current through LED ~20mA (will give a good bright light)
Voltage over LED @ 20mA ~1.5V (depends on the colour but 1.5V is a good starting value)
Now we know everything to get started.

We need a resistor to limit the current.
R = (9-1.5)V/20mA = 375 ohm. (Choose the closest higher value)
How much power does the resistor have to dissipate?
P = U*U/R = 7.5*7.5/375 = 0.15W. A 0.25W resistor is enough and is also a standard size.

Now put everything in series and we have light.

 

[Demon-Xanth]

Microcap has a free student demo, if you want to go that way. Usually, calculating it out first works for simple circuits because they're not very complex. Care to go into describing your design?

 

[FrustratedUser]

Share and we care.

 

[byak]

Ahh it was a challenge proposed by my brother. He described a small project with an IR sensor (phototransistor) and 9 IR superbright LEDs powered by an LED. Sensor gets input, 9 LEDs "light up" via 9V battery. He wants me to build one for him. Sounds interesting, might be fun to play with, and the parts are cheap.

Of course, numbers and battery sizes are sort of arbitrary. Thats the general idea, though.

I'm going to hit Radioshack tomorrow to get a handful of stuff to toy around with. Resistors, (visible light) LEDs, a project battery holder, etc. I guess thats a good place to start. Thanks for all the help thus far.

 

[FrustratedUser]

Something like this?

The values might be off. No real calculations were made. You probably need to amplify the signal from the Phototransistor.
But hey it's a start!

 

[byak]

Hey, yeah, something like that

How would I amplify a signal? I was thinking of using an SSR, though that is probably both extreme overkill, way too slow, and expensive.

What program did you make that in?

 

[amnesiac]

When I was in EE101 they gave us this radio shack kit that had tons of wires, LEDs, etc.. on this big board. You started off with really simple experiments (all detailed in the manual) from getting an LED lit up to using capacitors an IC, and a microphone to store and play back your voice with real time pitch modulation. It was wild and pretty cool considering it was just a mess of really really basic components. I learned a lot with it.

If you want to mess around a bit more with stuff you should get a breadboard. Makes putting things together a bit easier.

 

[FrustratedUser]

Circuitmaker 6 Student edition. Free limited useage. Up to 50 components or so including simulation.
Awesome!

Linkyfication

You could use another transistor.

Note:
I suck at designing with transistors.

 

[etech]

Instead of an SSR consider using a mosfet. Radio Shack used to sell a IRF510 that would handle about an amp of current with suitable heatsinking. The gate draws very little current and would be more suitable for a battery powered circuit than a transistor.

Mosfets are easy to design the drive circuit for the gate for the type of circuit you are designing. Simply put +5v on the gate and it will conduct and take the gate to ground and it is a very high impedance. Use a 2 to 3 k resistor to protect the gate.

You need to find out what the current draw of the LED you are planning on using. A 9v battery may not drive them for very long.


And yes, sketch it out by hand first and check and than double check your calculations. Components don't work all that well once you let the smoke inside of them out.