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Topic: 555 timer not resetting when connected to two relays... (Read 11062 times) previous topic - next topic

twang

hey polymorph,

Yes, I am using the 9v battery.
Are you saying that the relays are drawing too much power? If so, I think that the relays work just fine without the 555 circuit. These are 5vdc relays

Sorry about the pictorial, I am very accustomed to my SCH drawing software. I'll draw another one of what it is now.

I understand the diode I added did nothing, I have them parallel now.


But say... you have a transistor there to ground it. I'm using the 555 timer to send HIGH pulses straight to the coil. Are you suggesting that I should be sending HIGH pulses to ground the coil using the transistors?


twang

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 ... :(

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.

polymorph

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.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

TomGeorge

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

Tom.... :)
Everything runs on smoke, let the smoke out, it stops running....

polymorph

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?
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

twang

Hi,

I guess this forum has been long :P
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!

twang

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?

cjdelphi

Your schematic does not look right.

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



cjdelphi

I believe this is a wiring issue.

But really though, dump the relays for Transistors.

twang

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.

cjdelphi

Then it has to be a current issue then!

Measure the voltage drop of the battery when in atable.

twang

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?

twang


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...

twang

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?

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