Newb Questions

[duffman]

I was told that diodes draw about .6 volts of currents at the expense of making a current one-way. However, i was also told that LEDs, also diodes, do the same, and offer no drop in current, but do however, drop the current. .6 volts. is that correct?

I was also wondering about soldering. I have done a fair bit of it now, and it seems like somestimes I get a good connection and other times I dont. However, whenever I do get the minimal amount of solder onto the wire and the board it works fine. The joint doesnt look cold, even though not all hte braided wires may be covered with solder, or the solder is completely flat along the pc board. I have read a bunch of books on soldering, and alot of them warn about cold joints, whiskers causing shorts, but few actually talk about sloppy soldering. If you soldre a joint sloppily, can it cause increased resistances and drop in voltage?

 

[Nigel Goodwin]

I was told that diodes draw about .6 volts of currents at the expense of making a current one-way. However, i was also told that LEDs, also diodes, do the same, and offer no drop in current, but do however, drop the current. .6 volts. is that correct?

You seem rather confused about voltage and current, a forward biased silicon diodes drops about 0.7V across it, an LED drops considerably more, around 2-3V depending on colour. Neither of them really affect the current in any way.

I was also wondering about soldering. I have done a fair bit of it now, and it seems like somestimes I get a good connection and other times I dont. However, whenever I do get the minimal amount of solder onto the wire and the board it works fine. The joint doesnt look cold, even though not all hte braided wires may be covered with solder, or the solder is completely flat along the pc board. I have read a bunch of books on soldering, and alot of them warn about cold joints, whiskers causing shorts, but few actually talk about sloppy soldering. If you soldre a joint sloppily, can it cause increased resistances and drop in voltage?

A poor joint can cause a high resistance and give problems - it's VERY IMPORTANT that all services to be soldered are perfectly clean, it's even best not to touch them with your fingers as the grease from your skin doesn't help any!.

Generally you can tell by the look of a joint if it's good or not, it should have just the right amount of solder, and should be shiny and flowed smoothly all over both surfaces. If the joint looks dull, it's not soldered very well.

 

[ChrisP]

I was told that diodes draw about .6 volts of currents at the expense of making a current one-way. However, i was also told that LEDs, also diodes, do the same, and offer no drop in current, but do however, drop the current. .6 volts. is that correct?

Voltage is pressure, current is flow. Diodes drop voltage, not current. The specific voltage drop will depend primarily upon the material used in the construction of the diode. LED's are simply diodes that emit light. They too will allow current in one direction only, just as a "standard" diode will. This is evidenced by the fact the the diode will only light up when it passes current, which it will do only when properly forward biased.

I was also wondering about soldering. I have done a fair bit of it now, and it seems like somestimes I get a good connection and other times I dont. However, whenever I do get the minimal amount of solder onto the wire and the board it works fine. The joint doesnt look cold, even though not all hte braided wires may be covered with solder, or the solder is completely flat along the pc board. I have read a bunch of books on soldering, and alot of them warn about cold joints, whiskers causing shorts, but few actually talk about sloppy soldering. If you soldre a joint sloppily, can it cause increased resistances and drop in voltage?

Any poorly soldered joint will present the possibility of increased resistance in the joint. A good solder joint generally requires that a good physical (mechanical) joint be present first. Otherwise, the parts to be soldered may move during the soldering process, which will cause a poor finished joint to result.

The next thing is to apply just enough heat to allow the solder to flow. Many beginners make the mistake of trying to melt the solder with the iron and have it "drip" onto the joint, which is improper technique. Instead, apply the iron to the joint to heat the joint, and then apply the solder to the heated joint. The solder will be drawn into the joint when the joint is properly heated. "Cold" joints result from unequal heating between the parts to be joined, whikch often results from a loose mechanical connection between the barts, which in turn does not transfer the heat properly from one part to the other.

Be sure to protect heat-sensitive parts with heatsinks when soldering...

 

[ChrisP]

What Nigel said!

 

[duffman]

I have recently been doing the technique where you melt solder with the iron and it drips onto the joint. I have found it works perfect, however it would seem now that is the wrong way todo things. I have found however, that all other methods require too much heat. its like i have to wait 30 seconds just to get a piece of something hot enough to melft the solder. im using easy melt 60/40 solder, im using a 30 watt iron, so its not that. I dunno.

 

[Nigel Goodwin]

I have recently been doing the technique where you melt solder with the iron and it drips onto the joint. I have found it works perfect, however it would seem now that is the wrong way todo things. I have found however, that all other methods require too much heat. its like i have to wait 30 seconds just to get a piece of something hot enough to melft the solder. im using easy melt 60/40 solder, im using a 30 watt iron, so its not that. I dunno.

Yes, it's the wrong way - and it's not going to give very good joints, mainly because of the lack of flux. Electronics solder has cores of flux inside it, as you apply the solder to the joint the flux helps the solder to flow over the joint, it also helps to clean the surfaces as well.

By using the soldering iron as a 'spoon' the flux simply evaporates away, the smoke you get from soldering is actually the flux.

Your soldering iron tip should be lightly coated with a thin layer of solder, this will help contact between the tip and the joint - you apply the tip to the joint, and then the solder to the joint - it should only take seconds. If it's taking a long time for the joint to get warm enough it's probably because you don't have a thin layer of solder on the tip.

 

[laroche73]

Soldering

Nigel's given the best advice I've seen. Soldering is a little bit of an art, when you're good at it, you'll know. Clean joints, a tinned tip and a light touch make for good connections.

If it's taking a long time for the joint to get warm enough it's probably because you don't have a thin layer of solder on the tip

That's the most likely scenario. Or the joint's a heat sink. Ground and Vcc pads that connect to inner layers on a PC board take longer to heat up properly. Don't apply the solder to the joint until the pad has had time to get to (solder) melting temps.

 

[duffman]

I have another Newbie question. Would it be possible to replace a buzzer for a resistor with equal resistance?

 

[Exo]

probabely yes, but it won't buzz

 

[duffman]

I think you misunderstood. If i have a resistor in a schematic with a resistance of 100 ohms, can I switch it out for a buzzer that has 100 ohms of resistance, and still have the circuit work?