I am looking for ideas on a circuit, probably using a 555 to, after a start sequence is initiated, waits a period of time then turns on a supply voltage. Then after another period of time turns off the original supply and turns on an opposite polarity supply voltage.
lookup 555 sequencer, basically you cascade two or more 555s and each one triggers next one.
here is an example that uses three 555s
in this case U1 and U2 are triggered at the same time.
U1 powers one relay for some time
U3 does the same but it's trigger moment is delayed by U2
you can use DPDT relays, this will allow you not just to enable power to load but also to reverse it.
Do all the periods need to be individually adjustable, or could you use a 4017 decoded counter and have fixed ratio between periods, but the overall cycle time could be adjustable with a single 555 oscillator-clock?
The idea is to start a 12vdc motor that will open a slide in an instrument to allow a sample to be taken remotely.
The second timer would close the slide to contain the sample inside the instrument. This would require that the 12 volt motor runs in the opposite direction thus the need for polarity change.
Sensing the full open or full close could be done with proximity switches.