555 timer not resetting when connected to two relays...

To all:

After I followed all of your suggestions this is what the circuit came out to be: http://i.imgur.com/FawPWnN.jpg

I'm still running into the same problem ... :frowning:

It works on arduino as a clock, but not as 555.
I have not tried using 555 to use transistor to switch relay yet however; should it make a difference?
weeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee!

Wow this marquee thing is cool.

What are the coils of the relay rated at? 5V, OK, but what current?

I just grabbed an image from the internet to illustrate how the diode is connected. Whether or not the 555 can drive two relays without a driver transistor depends on three things: A robust battery of the -correct- voltage, how much current the relays require, and which version of the 555 is this? The TLC555 is CMOS (some others are, too) and won't source or sink enough current for any relay. The venerable TTL version of the 555 can source and sink 100mA or more. But there are probably 10 different versions of the 555 timer, all with slightly different characteristics.

Have you tried measuring battery voltage while this is operating? I would normally expect a stiff 9V supply to burn up a 5V relay coil.

Pin 4 -must- be connected to Vcc. It might work for a short time without doing so, but it will fail. That is the Enable pin.

Much clearer pictorial.

Hi, relay is 5V coil, 55R so 5/55= 90mA.
So in series with 9V, 9/110= 81mA, so 555 should handle current.

Tom.... :slight_smile:

But if not in series, 27 ohms on 9V is over 300mA, more that any 555 is rated to handle. And way more than a little 9V battery can handle.

If it is 7V without a load now, it is dead.

Put them in series as suggested with a new battery. We still need to know which 555 - SN555? NE555? TLC555? Some other variety?

Hi,

I guess this forum has been long :stuck_out_tongue:
Earlier I mentioned that I am using the KE17555.

Also, I ak pretty sure the circuit can handle the coil; I tried connecting pin 3 to the relays in parallel and in series, and I get pretty much the same results.

The 555 timer can turn ON the relays, but it cannot turn it off. How I enterpret this is that the 555 timer has enough power, if it can activate the coil.
I think I am misunderstanding something? Its likely that the folks helping me.are.saying something that is going right over my head...

Thanks!

And also, I have tried earlier connecting pin 4 to power, and it did not change anything. I will try one more time, as soon as I'm home.

But isn't pin 4 connected to Vcc internally, with a 100k resistor?

Your schematic does not look right.

Pin 2 detects a low signal.
Pin 6 detects high (causing pin 7 to discharge it)

I believe this is a wiring issue.

But really though, dump the relays for Transistors.

Huh...

It works without the relays though... If I were.to connect an LED with a resistor after pin 3 instead of a relay, it blinks fine.

I know that this circuit is not really common; I'm using a sort of extremely simplified version with less components. If you look at my original schematic at the beginning, you might notice it seems lacking, but it does work. I've used this minimalist circuit in other applications.

Then it has to be a current issue then!

Measure the voltage drop of the battery when in atable.

And about the relays to transistors,

I guess I could, but the whole point was to use the relay as the h-bridge, and not transistors, which would heat up and drop current. I also am on a budget so I don't want to buy any h-bridges

I think I should mentioned again that it works on Arduino With the blink sketch... If this circuit is not working should I just use arduino instead?

cjdelphi:
Then it has to be a current issue then!

Measure the voltage drop of the battery when in atable.

I'm a bit confused... The 555 timer is capable of activating the coils but NOT turning them off... There is enough power: voltage for sure, and current I'm assuming there is enough because the coils do activate.

It doesn't turn off. Instead it drops to something around 3 volts and you hear a faint buzzing sound from the relay as if it really wants to turn off but cannot...

Wait a minute I think I'm starting to understand: the 555 may have enough current to turn on the relay, but the current draw screws with the 555 and the 555 cannot turn pin 3 off?

Is that what everyone is trying to say?

The 555 charges a capacitor.
If it is at a certain level, the output is changed and the capacitor is discharged,

Your relays may draw too much current and cause the circuit to oscillate (which it was designed to do anyway, but at a different frequency).
That would be caused by an instable power to the entire circuit, triggered b y the relay current.
This oscillation is probably what you hear as the buzzing noise.
A diode can be compared to a transistor.
Why don't you try to use a transistor to switch the relays and see what that does for you?

A H bridge consists of transistors, but it can not be built with just a single transistor.

I think I finally get it now!
I will add a transistor and I will post about the results

MAS3:
Why don't you try to use a transistor to switch the relays and see what that does for you?

A H bridge consists of transistors, but it can not be built with just a single transistor.

I did not understand when it was mentioned to use transistors; I thought that I was being told to replace the relays with a 4 transistor h-bridge. I built this h-bridge before and I didn't like it. It drew too much current.

So this is what I plan to do with the transistor, the picture polymorph showed:

I'm not that transistor savvy :sweat_smile: ; I'm planning on using a 2n2222 with a 1k resistor before the base?
The last time I used the 2n2222 with 9v I ended up using the TIP 31 instead...

That should do.

Maybe it would be a good idea to play a bit more with transistors, because understanding those will be of great help to you in future projects.

Yea thanks a lot MAS3,

I've played with the 2n2222 before, but one project got me extremely confused.
I understand that by applying current to base (a small current; a signal) it will connect collector to emitter.
One project I applied small current to base and small current went through the collector to emitter; only when I had the same current did it flow properly.

The TIP 31 worked the way I expected it to.

I guess I will start playing with transistors more and try to learn the math.
wow, V=IR is still something hard for me to comprehend.

I will add a transistor soon and follow up with the results.

You keep saying "but it is working", but it is not or you wouldn't be here. Since you won't believe any of us about connecting pin 4 to Vcc:

  1. The reset pin (pin 4) is internally tied HIGH via approx 100k but it should not be left floating as stray pulses may reset the chip.

I cannot find any information on a KE17555 timer. I am familiar with the 7555 from a variety of manufacturers, they are CMOS 555 timers and don't do well with big loads on pin 3.

Thanks, polymorph,

I was misunderstanding the "current issue" the whole time it was mentioned :sweat_smile:
I'll tie pin 4 to Vcc and I will add a transistor... as soon as I can get my hands on this circuit again.