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I am working to replicate a timer circuit for an oxygen concentrator. It has 2 relays, each needs to go on for 4 seconds, off for 6, with a 1 second pause between each, picture isn't to scale, but should convey my meaning. Is this possible with a LM556, or should I use 2-3 LM555?

I tried looking into astable, monostable and bistable operations, but didn't find quite what I was looking for.

Waveform

Alan
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    Get a cheap microcontroller and write 20 lines of code. – Eugene Sh. Mar 02 '22 at 21:31
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    Are there any safety/environmental reasons why the application can't use a microcontroller, or any development costs reasons? (for the latter, test, documentation, manufacturing etc.) Important first step is to rule microcontrollers in or out. – TonyM Mar 02 '22 at 21:36
  • I could, I am just still a little shy about using them since I almost cooked my snakes.... I am a .NET developer, with 0 experience in python. So when I needed a humidity / temp controller, I built it in .NET Core, exported to Raspberry Pi and it worked, till it ran out of memory 22 hours later, and crashed with the relays (and heaters) powered on... Luckily, those particular tubs were still empty, still almost started a fire though. Never could figure out where the memory leak was. For this, I was hoping to hear this was a common type of situation that could be easily solved without software. – Alan Mar 02 '22 at 22:28
  • It can be done with a few chips (maybe just 74HCT4060 and some 74HCT138) or by one chip: an MCU or a CPLD. The last two are very cheap and you can buy cheap demo boards with everything you'll need on them. Makes building easy. It's then a few dozen lines of C or VHDL respectively, a couple of hours work all in plus any learning time. It comes down to your choice. – TonyM Mar 02 '22 at 22:40
  • I bet this could be done with a CD4047 and little else something would need to be done to get uneven pulses from the astable (eg: a diode and resistor parallel with the timing resistor) and something to combine the astable with the bistable. – Jasen Слава Україні Mar 03 '22 at 01:41

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A micro controller would be ideal for doing this.

You could however use a 555 timer running at 1Hz, a 4017 decade counter and a 4072 dual four input OR gate. The waveform can be sliced into 10 sections. Each of the 4 input OR gates could take 4 consecutive outputs from the decade counter to produce the black and red trace.

HandyHowie
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