Need help with a couple of 555 monostable circuits, trigger and reset

Thread Starter

CproAAC

Joined Mar 8, 2014
3
I'm just learning how to use the 555 timer and I can't figure this out. I'm looking for a couple of 555 monostable circuits

First one is the trigger longer than the output. I've searched but couldn't find any circuits that I could understand. I was able to find this youtube video watch?v=GnjbtXQG1ic that shows exactly what I want to do.

Second is the trigger and reset using the same push button switch. I want to use a button to activate the monostable timer. Let's say 30 seconds. Within that 30 seconds, if I want to end the output, I push the trigger button again to reset the timer.

Thanks in advance.
 

#12

Joined Nov 30, 2010
18,210
Back up. Think about what you need, and it isn't, "how to use the trigger pin as a stop command". The trigger pin will not re-start the time count and it will not stop the time count while a monostable configuration is running. You need to back up to what you need as a function, not, "how to make pins do what they weren't designed for".
 

Thread Starter

CproAAC

Joined Mar 8, 2014
3
I'm not asking how to make pins do what they're not designed to do. I'm asking for a circuit that can trigger (pin 2) and reset (pin 4) using the same switch.
 

ericgibbs

Joined Jan 29, 2010
10,814
I'm not asking how to make pins do what they're not designed to do. I'm asking for a circuit that can trigger (pin 2) and reset (pin 4) using the same switch.
hi,
Would a latching push switch be acceptable for your project.?

The type that push once latch ON and remain ON until pushed again for OFF and remain OFF.??

E

EDIT:
If yes, this circuit I did some time ago would work, adjust R1 C2 for 30 seconds
http://www.ebay.co.uk/sch/i.html?_nkw=latching+pushbutton+switches&lpid=25&keyword=latching+pushbutton+switches&clk_rvr_id=601594303880&crlp=21737301287_2683116_ICEP3&GUID=1720e48f1440a54c2621cdb1fdd5fc48&adpos=1s2&MT_ID=10&device=c&keyword=latching+pushbutton+switches&geo_id=32251&rotation_id=710-35648-5910-0&crdt=0&ff1=keyword=latching+pushbutton+switches&ff3=1&ff4=69_25&ff11=ICEP3.0.0&ff12=69&ff13=84&ff14=25&ff17=latching+pushbutton+switches
 

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DerStrom8

Joined Feb 20, 2011
2,390
I would use a j-k flip-flop between the switch and the 555, with Q1 connected to a transistor between pin 2 of the 555 and ground, and Q0 connected to a transistor between pin 4 and V+. The switch would be on the clock input of the flip-flop (connecting to +5v), and j and k would be connected to +5v. I think that would work, but I have to admit my brain hasn't been working very well lately. I'm sure someone would correct me if I'm wrong.

Good luck,
Matt
 
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Thread Starter

CproAAC

Joined Mar 8, 2014
3
I figured out the first problem. I've given up on the second problem. Now, I need help with another. How can I trigger and reset using positive voltage?
 

DerStrom8

Joined Feb 20, 2011
2,390
I figured out the first problem. I've given up on the second problem. Now, I need help with another. How can I trigger and reset using positive voltage?
I generally use a NPN transistor with the collector connected to pin 2 and the emitter connected to ground. Apply a positive current to the base and it will switch on, connecting pin 2 to ground, thus triggering (or depending on how you connect it, resetting) the 555.
 
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