Hello all! Let me first state that I am a noob to all this electrical stuff and I'm here just to learn and have fun with it, so please forgive my ignorance.

With that begin said, I decided to build the circuit that Bill designed (see below) and I don't know if my 555 timer is working correctly or anything for that matter. My led cycles on then off every ~2 min 40 sec (on ~1min 20 off ~ 1min 20). Is this correct? What exactly is the frequency of circuit? What is that measuring?

I have an old AC-DC power converter (power supply) that I was using to power this circuit, 12v @ 0.5amp. Is that enough power (amperage) to run this circuit?

Sorry for all the questions, but any help with this would be greatly appreciated.

I have basic electronic knowlege i.e. how to read a schematic, component types and how to use a MM.

Please reference the original thread posted by Chriswms17:
http://forum.allaboutcircuits.com/sh...ad.php?t=33015

 

Hello Clintb00,
There were a number of schematics posted in that thread.

Exactly which schematic did you build? It's a bit tough to guess without having a specific reference.

You tried to link to something, but it didn't post properly.

 

Hey Sgtwookie, thanks for the reply.

Hopefully this attachment will go through... Thanks!

 

Well, this is Bill Marsden's circuit.

Rather than me spending time analyzing it, he should be able to tell you right off what times/frequencies you should be seeing.

 

The OP got the link wrong.

http://forum.allaboutcircuits.com/showthread.php?t=33015

I left a reply that was left behind, so I will repost it here.

 

OK, this circuit was custom designed to be off for 8 hours and on for only 45 seconds. It is basically an oscillator.

Is this what you want?

This is a test circuit. It will work, but it won't be very accurate. The other gentleman was also new to electronics, most of my advice applies to you that I gave him, notably about protoboards. Do you know what a protoboard is?

I would place this circuit more for intermediate users. It is not a good one for beginners, but I'll help as best I can if you want to build it.

Have you seen these articles? They show examples how to use protoboards.

The 555 Projects

Bill's Index

This is the other schematic.

It is considerably more accurate, and harder to build. The crystal oscillator is sensitive, it can't be protoboarded (I think). Again, the comments to the original OP apply.

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Your proposed power supply sounds more than adequate. Measure the voltage on this power supply with no load, if it is a lot more than 12VDC it is not regulated. We may want to add a simple regulator circuit to it.

 

Yes, I would like the circuit to be off for ~ 8 hrs, and switch a relay for 45 seconds. The accuracy is not important. I would like to be able to adjust (increase or decrease) the cycle time. I'm assuming this can be done by installing a pot in the R3 position.

Are my cycle times for my LED correct ~1min 20 sec on & 1min 20 sec off?

Is the power supply that I'm using enought to trigger the relay and power this circuit?

What exactly is the Frequency measuring? From this equation and using the values for R2, R3, C1 and C9 as listed the frequency should be: 9.869e-2 Hz; is this correct? Is this counting the cycles / sec?

 

C1 and C9 are half the capacitance when put in series, this allow you to use easy to get electrolytic caps as opposed to a single unpolarized cap, which can be a pain to find.

So C in this case is 23.5µF. Figure that R3 should be mid range of its value (say 5KΩ) plus R2 (39KΩ) and you are closer to the calculation.

As for the LED, are you referring to D1 on the schematic? This is why I put designations, so you can refer to a part by name.

 

Yes, I thought that D1 was an LED. Is this not correct? Is there another LED in this circuit?

So, R3 is a rehostate. I will pick one of these and see if that helps. Thanks!

Just for future reference, when you hook up 2 capacitors in a series as shown in your schematic (C1 & C9) does the same formula apply even though they are wired with like poles; i.e. neg to neg Ct = 1/(1/C1+1/C2)? Is there any difference between wiring the circuit this way as opposed to neg to pos?

Thanks for your help Bill!

 

Sorry, I missed your post. Two electrolytic capacitors back to back like this are non polarized, half of each capacitors value, and double the voltage rating.

The capacitor in that oscillator must be nonpolarized but large, so it is a handy cheat. Just use the adjusted value in the equations, don't overcomplicate it.

Tantalum type capacitors are the most stable over time, though any type will work.

 

What exactly is the Frequency measuring? From this equation and using the values for R2, R3, C1 and C9 as listed the frequency should be: 9.869e-2 Hz; is this correct? Is this counting the cycles / sec?

This is 0.09869 Hz (=cycles per second) ie. much slower than 1 cycle per second
To get the number of seconds for 1 cycle do:
1/0.09869 = 10.1 seconds.

 

Don't forget the 10KΩ is a pot, so use 5KΩ for it's value. The period is 2.178 seconds, the frequency is .46Hz. The goal is .5Hz. That pot is to tweak it.

The LED is one for 128seconds, I think. Basically a quick and dirty calibration device.

The time base (which is what drove the design) is too fast, so I put a ÷4 counter in the circuit to slow it down. The time base comes out with 0.5Hz.