My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will be
ventilating by using a rollup side curtain. I plan to automate the process
by using a small 12 volt DC gear motor and wench. I've settled on my
mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few seconds
and go to delay timer. If you make Lo unroll a few seconds and go to delay
timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there an
inexpensive simple to program unit that runs on 12 volt DC? Alternatively, I
can see a way to do it with a timer that continuously does a few seconds on
then several minutes off continuously.

Karl