Using the same components for two 555 timers

Question

I am building a circuit to operate a Linear Actuator to open and close a lid.

The open and close times are the same.

The standard monostable circuit works.

There is one switch to tell if the lid is open or closed, it shows 12v+ when open and is grounded when closed.

I have built one timer unit. It works to specs.

I was wondering, since the timers will be the same, would it be possible to use the same components for both timers.

Pins 2 and 3 would use different triggers and the outputs would go to different places as well.

I would use jumpers between the two 555 Chips.

Basically my thought would be to connect all pins but 2 and 3 in parallel with each other.

Would this fly, or am I missing something.

It would be impossible (I trust) to trigger both timers at the same time.

Answer 1

The discharge output is low before and after the monostable pulse, so the outputs would remain low unless you triggered both 555 timers simultaneously.

Answer 2

No, that couldn't possibly work. You need separate (but the same value) components for each timer.

Answer 3

This idea will not work. The two 555 chips will need to have their own timing components. If you dig into the way a 555 chip works inside and what the waveforms on the various pins look like you would come to understand why this is not a feasible idea.

With that said there is another possible scheme that could be used. Since the open and close operation are mutually exclusive (i.e. would not be happening at the same time) it would be possible to use the time interval generated by a single 555 to cover both the operations. To do this some additional logic would have to be devised with logic gates or transistor circuits to channel the operation of 555 to the proper function.

I highly suspect that the extra logic to use one 555 far exceeds what you have envisioned doing with two 555 chips. So just bite the bullet and build your second timer circuit with the added capacitor and two or three additional resistors.