A few clearifications for an electronics newbie

[OldWolf]

Howdy all,

First of all, thanks for having this site here... I've been itching to learn electronics for quite some time now, and I've finally decided to get going on it!

I've read the very basics, resistors, current, power, etc. A few things are still a little unclear to me:
1. With regards to volts... let's say I have a piece that uses 6V, and a piece that uses 2V. If I run them in series, a 9V battery would be sufficient, as long as I added a resistor. Is that correct? (And the resistor would be found based on ohms law, rounding up... correct?)
2. What if I ran the two in parallel? Would I have to add a resistor to one of them for them to both function?
3. The above comes from a basic circuit I'm pondering on, which would have a buzzer and led both on, once current was provided to the circuit. Then, at a button push, the current would switch to a pair of wires to fire a firework. The idea came from several I saw online, but I'm trying to work up my own method so I can learn from it.
The buzzer I'm looking at as an example is here:
https://www.electro-tech-online.com/custompdfs/2009/02/KT-400463.pdf
It's data sheet indicates it's 'Rated voltage' is 12v... but it's 'Operating Voltage' is between 6 and 16. Does this mean that if I had a LED at 3v, I could run the two in series with a 9v battery and still have sound?
4. This gets a little more difficult to explain, but I'll try. Am I correct in my following guess:
If I'd like to instead have the option to fire up to four fireworks at once (on one button press)... do they still receive the same current/voltage, but the battery's life is consumed faster... or did I just skip a step?

Thank you very much! Your answers will help me learn much quicker!

 

[Chaerl]

Hi there,

I'll try to explain in a basic way.

Instead of piece, let's rename it as device (to be more technical). In a basic sense, you need to know that there are devices that "needs" certain voltage and others "drops" voltage. These are 2 different thing. If we say need, it will operate only at given voltage, less or more than the specified will not operate or worst destroys the device. If we say drops, if you satisfy the parameters of such device (like current, voltage threshold, etc.) it will always drops a constant voltage.

1. The 6V device is actually the buzzer, which will operate from 6V-16V with 140 ohms resistance. The LED is unknow yet. I could assume on how LED usually works. If you say its a 2V LED, That would be the forward biased voltage. Meaning, if you go below that, the diode is not forward biased (I hope you know the basics of semiconductors). And if the voltage is equal or more than the threshold, will drop 2V always. This is provided that you have proper load after the diode (like a resistor in series with the LED). So if you can properly calculate (not just by using ohm's law but using circuit analysis), it might work if the resistor is enough to drop about 1V and enough to provide the forward current of the LED that is not destructive. Also, try not to use the extreme limits of the device in designing. Like using 6V in a 6V-16V device. The problem is that, when you have voltage shifts, the circuit might not work as design for some instances.

2. Runing the 2 device in parallel is much easier. The buzzer can work at 9V so this is okay. The LED needs calculation to know the exact resistance for the LED to have the right forward current and if the package can withstand the power dissipation.

3. I don't understand what you're trying to describe with your circuit. It would be helpful if you have an initial schematic. But, I think I answered you're doubts here through my answers in 1 and 2.

4. What are you using to fire up your fireworks? Igniter like the one for the cars (cirgarette lighter)? If so, this kind of load would take up lots of current. It would definitely drain up your battery faster.

 

[OldWolf]

Thank you for your reply.

1. I am admittedly a little confused about needs/drops. I think the problem is that everything I've read so far has explained the basics of electronics, and what individual devices are/do (capacitors, transistors, etc.), but I haven't really found a good explanation of how all that works into circuits. What I'm trying to teach myself is not only how to follow a diagram, but how to both understand existing diagrams (what's actually happening there) and how to create my own based on something I want to accomplish... and I really can't find a good tutorial on that.

So it seems like a series LED/buzzer might be a bit over my head just yet, so let's go with parallel. I will certainly reread what you've written again later after I have more background knowledge because I'm sure it will be helpful, but for now lets push ahead on the easier topic.

It sounds like I'd be in even better shape if I increase my volts by upping my battery to 12... 8 AA's in series? lol Perhaps it would be easier for me to just find a less demanding buzzer.

2. Here's an LED I picked somewhat at random as an example:
SLA-560LT3F

According to it's specs, it's forward is 1.75V, and it's operating current is 50mA... so to determine the resistance needed if I were to use that buzzer mentioned in parallel with it, on a 9V battery, would I do (9-1.75)/.05 = 145ohms... so a 145 ohm resistor in series with the LED, and that all parallel to the buzzer? *crosses fingers*

3. Basically, this led/buzzer would be on it's own separate circuit (is there a different word for that?). Basically, when the button is pushed down, the current switches off of this buzzer/led circuit, and onto the firing circuit. The idea is when the system is turned on (power connected, and a switch flipped... those are easy to do which is why I didn't mention them), it turns on the LED light and buzzes to indicate it's "hot." Then when the 'fire' button is pushed down, all the juice is switched to the wires running to the firework. Hopefully that makes sense... I'm not sure I'm capable of drawing a diagram, but I can try if I'm still not making sense.

4. I'm actually hoping to use a rechargeable battery of some kind eventually (I'm thinking an RC car battery, I have a couple lying around), but for my initial planning I'm trying to keep it simple. The actual firing mechanism will be two alligator clamps with both the firework fuse and a piece of wire... I believe it was nicrome, which according to what I've read is supposed to get hot very quickly. I've also thought about just using some steel wool. I'd be interested to hear better ideas though, my goal is to make it easy to hook up, but very fast. I thought about using the filament from inside of a Christmas bulb, but it sounds like a pain to harvest... and only a one time use.

Thanks again!

 

[audioguru]

I think the "buzzer" is actually a little speaker that needs 12VAC from an audio amplifier and tone generator and will just click one time with DC.
You need a piezo beeper that has a built-in oscillator circuit so it works on DC.

 

[Chaerl]

Nothing to worry on my side.

1. Don't worry, everybody starts from zero. I went to that stage also, I understand your doubts. Basically, what you've done is great. Knowing first the basics of each components (resistor, capacitors, transistors, etc.). After that, you must know the principles on how each component works, theoretically and mathematically. After which, I suggest to go for circuit analysis. I don't know any website for tutorials. All I have is based on my experience in designing at work. Maybe others can help you through this thread.

Yeah, I would suggest to go on parallel. It would be easier. Don't try to dig deeper into this simple circuit, you might be discourage if you seen complicated one. lol.

2. You're calculation is correct. But just to be safe, use higher than 145 ohms, not lower. Not to high also because it might dim your LED. I would say 200 ohms is enough. Resistors have tolerances, you might fall at the limit where your LED will be the fireworks.

3. I got your point now and I could imagine the circuit. I'm good at imagining. hehehe. The LED/Buzzer can be called sub-circuit and the whole design we can call it as module or system. This is not standard naming, but I usually use this terms.

4. The nicrome is a good heating element. But with your design, you're actually shorting your battery because the nicrome is a very low resistance. It might blown the fuse, but depends on the current capability of your battery. If you use the car battery, its unlimited current. It will give what is demanded and in return, fast drain. I would suggest to add a resistor in series of the nicrome. The value would depend on the material (nicrome). What you need to do is to compute how much current needed is enough for the nicrome to ignite. It's more on the characteristic of the material. I'm not good at that point.

BTW, the buzzer say its magnitec. Maybe a DC voltage is enough to trigger a buzzing sound. But, I'm not sure. Try to search more about this stuff also.

You are welcome.

 

[iflymyhelishigh]

Piezo buzzers are the ones that you hear go BEEEEEEEEEEEEEEEEEEP a high shrill.

 

[OldWolf]

I think the "buzzer" is actually a little speaker that needs 12VAC from an audio amplifier and tone generator and will just click one time with DC.
You need a piezo beeper that has a built-in oscillator circuit so it works on DC.

I'll poke around and see if I can track something down. What I'm hoping for is a lower tone buzz, rather than a beep. I might just drop the idea though, it might be pretty annoying, even if it's only going to be on a short time. The main point of it was an audible noise to warn me that the system was armed so I didn't try to connect something and get a premature shot. It shouldn't happen anyway unless I push the fire button... but the idea was just to have multiple fail safes.

Nothing to worry on my side.

1. Don't worry, everybody starts from zero. I went to that stage also, I understand your doubts. Basically, what you've done is great. Knowing first the basics of each components (resistor, capacitors, transistors, etc.). After that, you must know the principles on how each component works, theoretically and mathematically. After which, I suggest to go for circuit analysis. I don't know any website for tutorials. All I have is based on my experience in designing at work. Maybe others can help you through this thread.

Yeah, I would suggest to go on parallel. It would be easier. Don't try to dig deeper into this simple circuit, you might be discourage if you seen complicated one. lol.

Agreed, I'll keep it simple. I have a book I'm looking into that might get me further, but I wont have time for it until next weekend, he he.

2. You're calculation is correct. But just to be safe, use higher than 145 ohms, not lower. Not to high also because it might dim your LED. I would say 200 ohms is enough. Resistors have tolerances, you might fall at the limit where your LED will be the fireworks.

I had actually read someone say to double it, but that seemed a little extreme, so thank you for that number, that should help. I've actually already burned out a LED (and my finger, lol) when I first started learning. I got a little ahead of myself and put a battery against a LED, no resistor. Burned the snot out of my finger and ruined the LED, which was built into a board. :/

3. I got your point now and I could imagine the circuit. I'm good at imagining. hehehe. The LED/Buzzer can be called sub-circuit and the whole design we can call it as module or system. This is not standard naming, but I usually use this terms.

Thanks, I'll go with that then.

4. The nicrome is a good heating element. But with your design, you're actually shorting your battery because the nicrome is a very low resistance. It might blown the fuse, but depends on the current capability of your battery. If you use the car battery, its unlimited current. It will give what is demanded and in return, fast drain. I would suggest to add a resistor in series of the nicrome. The value would depend on the material (nicrome). What you need to do is to compute how much current needed is enough for the nicrome to ignite. It's more on the characteristic of the material. I'm not good at that point.

If I understand it correctly, it's not exactly resist-less. One thing I might not have made clear is that there are wires running from the station to the fireworks, which will be fairly lengthy (in fact, they'll be as long as I can run them without loosing the power I need to heat the wire, hopefully around 20'). Also, if I'm reading it right, the Nichrome's resistance is 65 times that of copper, but the length wont be a lot, so I might get a little bit there as well.

The reason I didn't add any other resistors is simply because the other examples I looked at didn't seem to have them, but I don't know how their power sources did over time. I'm hoping that since they will only be fired for a second or two, it wont drain the battery super fast, but I'm not sure how that works exactly.

Thanks!

 

[OldWolf]

[whoops, loll]

 

[Chaerl]

Hi... I think everything is clear.

One thing, I didn't know really the exact resistance of nicrome. The higher the better. In the design, it's fair to assume that the wire have no resistance (though in reality there are few milliohms or sometimes 1 ohm). You are right, taking into account its just short duration time for pressing the buttom. Maybe its not that significant.

You may also calculate how does the battery last using the AH (ampere-hour) rating. This is if you're interested as to how many presses before the battery runs out. But, this is more complicated than you thought.

 

[OldWolf]

Here's a follow up question actually:

I'm looking at using a cheap 12v battery like this one, because I could recharge it, and I'm almost guaranteed to have the necessary amps for my project:
**broken link removed**

My question then is simple: it's not possible for me to burn my devices/wires out as long as I have fair resistance against the current with only a 12v battery, correct? In order for it to destroy the wires, wouldn't it need high voltage and current both?

I'm a little shaky using a 12v, but I've read that aside from the ever so slight chance they might blow up in your face if you cause sparks near them, they're otherwise safe (can't do much more than give you a decent shock). Is this true?

Thanks!

 

[Chaerl]

Nothing will be burned up if you properly calculated the requirements and consider all the parameters. Even if you have the right resistance, it doesn't mean the resistor will not blow up. We need to consider the power and the energy applied to each components. I know I'm talking a bit more advance, but you need to note this stuff also. In order to know that things will not blown up, calculated the power, energy, voltage, or whatever is necessary and compare it against the ratings of your devices or components. Do you know what I mean? Even the wires have ratings on how much current and voltage it can take.

Any how, its not the voltage nor current that can destroy an electronic component. It is the energy applied to it. Just make sure that the components can withstand the given energy. Few notes below.

E=P*t
P=I*V

E=energy
P=power
t=time
I=current
V=voltage

Hope this helps

 

[audioguru]

The tiny cheap Chinese battery has hardly any capacity (like AAA Ni-MH cells). It will quickly be destroyed if it is discharged too low.

It is sealed so it won't produce hydrogen if it is not over-charged. It takes many hours for it to charge.

 

[OldWolf]

The tiny cheap Chinese battery has hardly any capacity (like AAA Ni-MH cells). It will quickly be destroyed if it is discharged too low.

That doesn't sound good... could you elaborate on that point a bit?

Nothing will be burned up if you properly calculated the requirements and consider all the parameters. Even if you have the right resistance, it doesn't mean the resistor will not blow up. We need to consider the power and the energy applied to each components. I know I'm talking a bit more advance, but you need to note this stuff also. In order to know that things will not blown up, calculated the power, energy, voltage, or whatever is necessary and compare it against the ratings of your devices or components. Do you know what I mean? Even the wires have ratings on how much current and voltage it can take.

Any how, its not the voltage nor current that can destroy an electronic component. It is the energy applied to it. Just make sure that the components can withstand the given energy. Few notes below.

Ah, ok... chances are the stuff I'm working with is going to have a very low rating, but I don't have access to data sheets on any of it as it was part of a mixed pack of starter junk.

 

[audioguru]

That doesn't sound good... could you elaborate on that point a bit?

The cheap battery is only 1.2Ah which is almost the same as tiny AAA Ni-MH cells.
It is lead-acid which is destroyed if it is discharged too low.

AAA Ni-MH cells have a capacity almost the same and can be discharged to zero thousands of times.

 

[OldWolf]

So you'd suggest just a long chain of AAAs?

 

[audioguru]

I suggest using ten AA Ni-MH rechargeable cells in series to make 12v for more than double the time of the cheap Chinese battery. They can be charged in a hurry if you want.

 

[OldWolf]

Do you happen to know of a reasonably priced charger with a smart chip in it for those? I actually looked into getting rechargeable in the past, but the darn chargers were extremely expensive if I wanted to get anything that wouldn't let them over charge.

Thanks!

 

[audioguru]

I can buy name-brand AA Ni-MH cells that come with a low price fast charger.
What is a low price for me might cost too much for you.

 

[OldWolf]

Ok, I'll rephrase. See, I already have a car battery charger, so for that route the charger would be free. So since this is a low budget project, I wouldn't want to spend more than 30 on batteries and a charger... but I really need a charger with a smart chip so there's no chance I'll over charge them by forgetting about them.