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Astable 555 controlling an astable 555

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davkrat

New Member
Hello this is my first post. I have been trying to deverlop a circuit to turn a small 12V pump on and off in a cycle of pulses. All the schematics I have found show a monostable 555 controlling an astable 555. I do not want to have to manually press a switch. I want to be able to connect the power and let the pumps run through their cycle continuously. I am hoping to have the controlling astable on for 6 seconds then off for 4 seconds. I can play with the C, R1 and R2 values too get the timing right. I want the second astable to pulse 1 sec. on 1 sec. off. I want the overall cycle to look like this:

(1 - 0 - 1 - 0 -1 - 0) - (0 - 0 - 0 - 0)

I believe I can get the output of the first astable to trigger/reset the shorter duration pulses of the second. Is that correct or should I be looking for a different IC. Thanks, I hope my description is clear. I have tried getting the output of the first 555 to reset pin 4 of the second, I also tried to set it up to drain the capacitor of the second. The end result is more a combination of the two timers cancelling eachother out. I either get a very fast pulse or more of a average of the two timing cycles. I have not played with electronics in quite some time. In highschool I used to build effects pedals for my electric guitar so I have a very basic understanding of electronics. Thank you for your help.
 

MikeMl

Well-Known Member
Most Helpful Member
How about an astable (555 or one made out of a CMOS hex inverter) driving a CMOS counter like a 4017. You can "OR" together the respective outputs to create the desired cadence, as long as the cycle repeats on any integer between 2 and 10.
 

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davkrat

New Member
Does the 4017 run through the sequence once and then need to be reset by the 555? That sounds like it might work great, I don't have any experience with a 4017 but maybe I'll pick some up and give it a go.
 

MikeMl

Well-Known Member
Most Helpful Member
Does the 4017 run through the sequence once and then need to be reset by the 555? That sounds like it might work great, I don't have any experience with a 4017 but maybe I'll pick some up and give it a go.

I added a sample circuit to my previous post.
 

davkrat

New Member
Thanks, if I understand the 4017 right each time the 555 output goes high it pushes the 4017 onto the next step in the sequence correct? I never understood how you control the duration of the 4017 steps. I believe it is the overall on/off cycle (t1+t2) of the 555 that determines the duration of each step in the sequence. If so that is exactly what I am looking for.
Thank you!
 
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