Problem w/astable flasher circuit

[tap364]

Hi all, I'm having trouble with a simple 2 NPN transistor astable flasher circuit. It's a typical circuit seen everywhere and my outputs on each side are driving solid state relays that turn on a string of C7 lights each cycle. My timings are long, about 3sec on, 5sec off, and the circuit works fine. The problem is when I breadboard 3 or 4 circuits together all with different timings, they tend to start "synching up", flashing together, rather than maintaining their individual flash rates. I've tried different RC values and still have the same problem. Does this sound like normal behaviour when running these circuits together? My bench supply is a very stable DC, so I don't think it's power related noise. I figure that when one circuit switches, it's also triggering another circuit that's close to its switch point. Is there a way to isolate them without using separate supplies for each circuit? I eventually would like to run the finished board with a simple (and cheap) 6-12V wall wart. Is there a better circuit to do what I need, i.e. 555? My projects will need from 3 to 6 of these flasher circuits on a single board eventually. If I need to provide any more details I will do so gladly! Thanks for any insight into this. TP

 

[ericgibbs]

hi,
What onboard power rail decoupling caps do you have.? electrolytic and ceramic.?

 

[tap364]

Hi Eric, thanks for the reply. Sadly I had no caps on the power rails. Your suggestion prompted me to research the use of decoupling caps. Put a 103M ceramic across each stage and the circuit is working perfectly! Will probably need some filter caps when switching to the wall wart though. Still learning, just needed a nudge in the right direction. Thanks again! TP

 

[eblc1388]

The problem is when I breadboard 3 or 4 circuits together all with different timings, they tend to start "synching up", flashing together, rather than maintaining their individual flash rates.

Nice. Many years ago some scientists also discover that different mechanical clocks also sync together if they are placed on the same shelf. I guess this is the equivalent in the electronic world.

Sadly its the fact of life that it happens when one don't won't it to happen, and people have gone to great trouble to make it happen but they just won't.

I would say for sure if one starts out "to make 3 or 4 circuits together" hoping they would sync in flashing would end up having each circuit flashing by its own.

 

[tap364]

Never heard of the clock analogy before. However, I have heard of fireflys syncing their cycle after awhile. Apparently true also with a group of female co-workers, if you know what I mean . But you're right, would never happen if that's what I wanted.