So I bought my arduino a week ago and have been scavenging old electronics for parts. One of the parts I scavenged was a 470 uF/6.3V capacitor. I noticed it had two crevices on the bottom where it used to be connected by wires, so I stuck my own wires into it. Now, from my understanding a capacitor is supposed to store charge until the voltage drop across the plates is equal to to the power source's potential difference, at which point it'll close and act like an open switch. My problem is that even though I've hooked up a capacitor, a resistor and an led in series to the 5V pin, the capacitor just acts like a wire and the led stays on forever. Am I doing something wrong? Is the capacitor messed up because I just stuck some random wires in it to replace the ones that were used to solder it to its previous board?
Oh, also, where can I get cheap electronics? I've looking at Radio Shack for random things like leds, potentiometers, photocells, etc. but the prices are crazy. I really want a potentiometer, but not if it's $5. $2 for an led... they must be crazy.
If it helps, I live in Florida, zipcode is 32931.
If you wired the capacitor in series, it shouldn't light the LED up at all, since capacitors block DC. Posting a pic would help.
And regarding cheap electronics: eBay. It'll take 2 or 3 weeks to get stuff, but it's hard to find anything cheaper.
Okay, that clears things up a bit. I never knew the type of current actually mattered (I've only taken a basic introductory physics class). What's the logic behind it?
As for the capacitor, I guess I messed it up. Wasn't exactly gentle with it.
Now, from my understanding a capacitor is supposed to store charge until the voltage drop across the plates is equal to to the power source's potential difference, at which point it'll close and act like an open switch.
That isn't correct, but maybe it's just your choice of words. A capacitor when wired to a voltage source will draw current from that source until it's charge voltage is equal to the source voltage, at which time current flow will cease. Then it will just hold that charge voltage unless some connected load draws current from the cap, which will discharging the caps stored voltage. But if the cap is still wired to the voltage source then the load's current draw will come from the voltage source and the caps charge will remain equal to the source voltage. Words like 'close' and open' do not apply to any capacitor's behaviour in any circuit I can think of at the moment.
As far as cheap parts go, the very best prices I find are via Asian sellers on E-bay. I recently bought two pots for $1 each which included free shipping and they were definitely brand new unused parts. I don't know how they do it as the quality of the pots met my needs and expectations. I do have to wait for around 10-12 days for delivery, but to me the wait is well worth the cost savings.
Lefty
If you want to get some cheap LED's look at Radio Shack.
I know you said you already looked there and it is true most are like $3 for one LED, you can get a good deal if you find the assorted bag of 20 LED's for $2.50. It is normally in the very back of the LED drawer.
If you can find it you can get yourself a great deal!
-TECman-
TECman:
If you want to get some cheap LED's look at Radio Shack.I know you said you already looked there and it is true most are like $3 for one LED, you can get a good deal if you find the assorted bag of 20 LED's for $2.50. It is normally in the very back of the LED drawer.
If you can find it you can get yourself a great deal!
-TECman-
Or you can get 100 red leds for like 3 cents a peice with free shipment.
Lefty
Yup, badly chosen words on my part. Looks like ebay it is.
The best source of parts on the cheap is getting them from other electronics but you are left with questionable parts.
The worst night mare is intermittent failures on parts. Especially when the part is cold and it works then when it it is working it heats up then fails.
Find a good electronics magazine like Nuts & Volts and in the back you will find lots of parts suppliers that have grab bags for 5-10-20 bucks that have a lot of good parts.
There are other like mouser , Digikey ect. ect.
eejdoowad:
One of the parts I scavenged was a 470 uF/6.3V capacitor. I noticed it had two crevices on the bottom where it used to be connected by wires, so I stuck my own wires into it.
Am I doing something wrong? Is the capacitor messed up because I just stuck some random wires in it to replace the ones that were used to solder it to its previous board?
Is this capacitor an SMT part or is it a traditional part (any picture, or find something similar on the web as a reference for us), because it could be that the part was torn from a pcb and the terminals have been ripped out.
If the terminals were ripped out, then you need to throw the part away, because sticking wires back in, will not work, and would result in a 1:1 short. (possibly resulting in what you are seeing)
You usually get better documentation and support if you buy from a reputable seller(I've really only bought from SparkFun and eBay before), but pretty much everything that I've bought from eBay has worked fine, with the exception of some parts looking slightly used or old
If you're just getting started, some "parts kits" from places like Amazon will help get you set up with resistors, capacitors, LEDs, etc.
You probably also want some set of transistors (some generic PNP and NPN ones, and some generic N-channel mosfets) and perhaps some cheap utility ICs, like 338 comparators, 555 timers, 601 opamps, etc. Many of those can be had 10 for $4 or so ($0.40 each) from distributors like digi-key. You probably also want a couple of 7805s for voltage regulation, a couple of pots and switches to re-use.
If you can build up an order on digi-key, and then ship using first-class mail or priority mail, you'll get your stuff in 3 days, and pay no more than $5 or so for shipping.
Ebay is best for cheap thing like resistors and leds, maybe some ics
but for the bigger ticket items like screens or boards go with an actual online store, I spent a week trying to figure out why a touchscreen from adafruit wasn't working properly, I even blew 40$ on another thinking I messed it up, turns out it was a bad pin on the "brand new" mega2560 board I bought on ebay for 30$
it really sucks when something like that happens, so be cheap but not where it counts