donelly

modified 7 years ago

Independently Variable Timing for both portions of output x2

159

02:15:16

This is a circuit by Rob Paisley which enables independent adjustment of the on and off times of an LED. I have put two of these circuits in series so that, operating out of phase, they simulate random operation of the second LED. This will be a flickering LED and will light up a welding shop on a model railroad.
These circuits work individually in everycircuit but not together. Is this beyond the abilities of the program or am I doing something wrong?
Any help would be much appreciated.

D

Thanks to hurz and others who gave advice on this. It works now and I will build it this way.

published 7 years ago

kiani

7 years ago

Am no expert but you have a transistor with no resistors in collector or emitter circuit,, i added two 10 k resistors in series with collector and emitter, and started to work.

kiani

7 years ago

http://everycircuit.com/circuit/4551558682640384

hurz

7 years ago

Comments in description, check this http://everycircuit.com/circuit/6105584821862400

BillyT

7 years ago

Hurz circuit works well, adjust the time base to 1 second to see what it would look like in real time. For a welding simulator, would a smaller capacitor on the 555s be a better starting option?

donelly

7 years ago

Thanks hurz. That works.

hurz

7 years ago

But still open poti pins. Not used reset pin. Not removed transistor which will pump current into 555, cuz there is a back feed diode in collector missing. I would remove the transistor and use the reset pin instead.

donelly

7 years ago

If I don't use the transistor then the second circuit will start timing every time the first one fires, so the flash sequence will not be random but will be the same each time. This way the second circuit keeps timing continuously and the transistor switches the output to emulate random. I have tied back the unused terminals of the pots. Thanks for your comments hurz. I am new at this.

kiani

7 years ago

http://everycircuit.com/circuit/4551558682640384. How about this?!

hurz

7 years ago

@kiani, you control the second 555 by power which will have the same effect which donelly dont want. He likes to have the second timer continues running so the on/off Timing is equaly distributed over time.

hurz

7 years ago

@donelly, if the timing is so importante for your circuit check this, but keep in mind your idea does choop the signals to probably very small pulses at beginnig which might cause trouble http://everycircuit.com/circuit/5806954051272704

hurz

7 years ago

I have changed it to a common emitter solution which is better then a common collector with back feed protection. Check again this circuit http://everycircuit.com/circuit/5806954051272704

donelly

7 years ago

I accept that your last solution is better hurz, it is certainly more elegant, but I do not understand why it is better. Nonetheless I will build it your way. Thanks for the time you have spent on this and thank you too kianu for your comments.

hurz

7 years ago

You are welcome!

hurz

7 years ago

Here a simplified model of what you have with a common collector circuit while the collector is switched in voltage. The power sources represent the 555 outputs you can switch and see how the current is going from base to collector without backfeed diode and might cause damage to components or unspecified behaviour to the transistor. Check this, maybe it helps to understand why i prefer a common emitter circuit. http://everycircuit.com/circuit/4822328050712576

BillyT

7 years ago

Before reading hurz comments I came up with the following circuit, after reading hurz's comments, I still think that the circuit is ok, the biasing resistor should limit the base leakage current to a non critical level. http://everycircuit.com/circuit/5998033253957632

hurz

7 years ago

But BillyT, you present exactly what i have recommended with an common emitter, don't get your comment.

BillyT

7 years ago

I wasn't sure if the power coming from the second 555 would be a problem.

hurz

7 years ago

Thats a problem, current flows from collector to the base into 555.

BillyT

7 years ago

Surely that would happen in either circuit, but the value of the biasing resistor would limit the base current to a very low value.

hurz

7 years ago

And this current multiplied the Hfe would be quite limited as emitter current. So common collector is not a good idea. The solution is common emitter. Cuz the current into base wont go the collector way only to ground.

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