Electronics > Beginners
555 Problem
(1/2) > >>
codingwithethanol:
I designed a small circuit for a friend of mine, and it was working fine up until a certain point and now I'm seeing some odd behavior. Basically I just have two 555 timers, the output of one controls the other via the control pin. The problem is that when i turn it on it will only work for one cycle, and then give up. I probed around and discovered that the capacitor isn't discharging through the timer, even though its at 2/3 Vcc. I have no clue what the issue is, as the circuit worked flawlessly when it was breadboarded. Any help given would be very much appreciated.
mikerj:
You don't have any supply decoupling capacitors.
codingwithethanol:
I didn't think it'd be an issue, but ill add some. I'm getting stable 5V, this seems to be an issue with the 555



codingwithethanol:
I added the caps as per the suggestion but the situation is the same
floobydust:
I see a few issues with the circuit.
I don't see the approach working because the second 555 timer control voltage pin 5 is driven hard to near 0V or 5V so it can't oscillate. If your 5V rail was really noisy, which it should be with no decoupling cap or a weak battery, the circuit might have fluked and worked due to it's own noisy power.
If you want timer 1 to gate timer 2, try connect timer 1 pin3 to timer 2 pin 4 instead of pin 5.

If the pot across pin 7-8 is dialed to zero ohms, it can damage that 555 due to overcurrent on the discharge pin. You need a small series resistor to prevent that like, maybe 220R.

I would add a 10-100uF cap across the 5V rail because a heavy speaker load does make power noisy. You don't even need the 5V reg and can run the 555's direct off 9V - if you have good bulk capacitance across the 9V. It would be pretty loud though and have to add a resistor.
The loudspeaker out diode seems not the greatest, it does not limit the current into the loudspeaker enough and the 555 can only push the speaker cone out and not in. Instead of the diode, use a resistor 47-220R to drive the speaker.
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod