help from electronics gurus? 555 timer

[kwirky]

here are the specs for the 555 timer I have:
supply: 18V max (normal 4.5-16v)
power dissipation: 600mw
output current (sink or source): 200mA
operating temperature: 0 C to 70C

the relay I have has the following specs:
core resistance: 200 ohms
nominal current: 60mA
DPDT 5A at 120VAC

I have the following AC adapters to play with:
6V 300ma
12V 1.5A

I've been following this tutorial:
http://www.geocities.com/SiliconValley/2072/proj2.htm

and I've melted my 555 timer to my breadboard :redface:

Anyone able to help? I'm planning on using a potentiometer to adjust the time for the timer between 30 seconds and aprox 10 min. 30 sec - 5 min would be OK too.

Also, how can I identify an electrolytic capacitor? I've seen most diagrams call for one, but I can't tell if any of mine are electrolytic?

this is all pretty new to me, and any help'd be great

oh and I found a nice calculator here:
http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm

[mwafler]

First, I don't know how you melted a 555, they're pretty robust. For the capacitor, this should help. http://en.wikipedia.org/wiki/Electrolytic_capacitor
What are you trying to accomplish with this circuit?

[midgetwaiter]

He's probably making a wave timer, using the relay to control a couple of powerheads. Best to use Maxijets in this situation as they are the only powerheads that can handle the frequent starts well.

I can't imagine how you melted that chip. Are you sure you didn't short it somewhere?

Here's a cool wavemaker circut

http://ealex.aqua-web.org/wavebox/circuit.htm

[kwirky]

I didn't really melt the chip, but I exchanged it at work anyways just in case. The breadboard melted where the contacts from the chip came in though.

I've done a lot more research today, and now it's the fun part of sourcing out a 0.1 uf electrolytic capacitor.

[KrazyKuch]

here download this program....tells you everything you need!!!

http://555-timer.clarkson-uk.com/program.html

[kwirky]

Ok, I'm using a 5V 600mah power source so that my new breadboard doesn't melt out or nothing.

i'm sounding like a bother asking all these questions. But if it says it needs an electrolytic capacitor, I gotta use an electrolytic capacitor, don't I?

I have a pack of various mica capacitors that do like 0.1 and 0.68 uF, but all these schematics call for electrolytic capacitors.

The mica capacitors I have are 200V ones, pretty hefty ones like 1/2" large. Are these meant for large AC projects or something? I'm guessing that's why nothing's working.

[beaker020]

an electrolytic capacitor is packaged in a metal can. Although, I've never seen an electrolytic under 1uF, I understand they are available as low as 0.47uF. I dont think a 0.1 uF electrolytic exists. Remember that the formula calculates capacitance in Farads. 1Farad = 1000 uFaradsIn most cases it doesnt matter what type of capacitor you use, as long as the value and voltage ratings are acceptable. Electrolytics have high leakage and their values drift with temperature. They are great for power filtering and it would work fine but for reliable timing operations I would recommmend Tantalum. I would also reccomend a 0.1 uF ceramic cap across your power rails and from pin 5 to ground.

[kwirky]

are tantalum capacitors polarized? Like, is there a +/- to them like the canister ones?

[beaker020]

yes they are polarized. you should probably be looking in the range of 100uF

[kwirky]

I got it working with an aluminum capacitor!

this link helped a lot: http://www.iguanalabs.com/555kit.htm

It's just blinking an LED on 15 seconds, off 15 seconds. Now to find myself a 12V 300ma power adapter (for the relay).

I've only got the one 100uF aluminum capacitor. I omitted the 0.01uF capacitor I've seen in most of the other schematics by following the link above and it worked. Know how this would affect it in the long run?

Oh, and how does one wire up a snubber? does the uF and the resistance have to be calculated?

[kwirky]

I got it working with an aluminum capacitor!

this link helped a lot: http://www.iguanalabs.com/555kit.htm

It's just blinking an LED on 15 seconds, off 15 seconds. Now to find myself a 12V 300ma power adapter (for the relay).

I've only got the one 100uF aluminum capacitor. I omitted the 0.01uF capacitor which I saw in most of the other schematics. I followed the directions in the above link and it worked anyways. Know how this would affect it in the long run?

Oh, and how does one wire up a snubber? does the uF and the resistance have to be calculated?

[kwirky]

just an update.

I got the prototype working. It's adjustable from 5 seconds to 1.5 minutes for each pump, and I have a switch that will shut off all the pumps for 3 minutes for feeding.

I tried to get the 555 to go through a JK flip flop for a 50% duty cycle, but output (O) of the JK chip doesn't actually reach 0 V/I, so it wouldn't trigger the amplifying transistor to shut off. So I only used the 555 with a resistor combo that gives as close to a 50% duty as possible.

When the final circuit board is soldered up, I'll post pics schematic diagrams. I'll have enough parts left over too in case anyone wants me to build them one or two. I'd do it for pretty cheap.