how do you get a controllable modulated (0-10v) signal from a 24v transformer?

Question

had this cool idea the other day. One of the 1st laws of Thermodynamics says hot air rises and cool air falls. I live in a two story home and in the summer time all is well but in the winter time the second floor is hot as heck while the first floor maintains the setpoint of the thermostat. for the last couple of years, during winter time, I have been closing the diffusers on the second floor and this has worked fairly well but is no fun. I want to go overboard with overcomplicating this so I got ahold of some damper actuators that are 0-10v and I figured I would install another stat (RTD) to drive the motor to maintain temperature -- "easier said than done"!. how do you get a modulated signal out of a constant source without going to Graingers and buying there PID controllers that are way overpriced?

Answer 1

If you are looking for a 0 -10 volt DC modulated voltage, you can fabricate a small circuit using an LM317T Pos (NTE956 / RS 276-1778). It is a very simple circuit using 2 capacitors, an on/off switch, 1 resister and a potentiometer for adjustment. Depending on the current draw, it is always a good idea to use a heat sink on the regulator.
I have used this circuit many times to adjust 12 or 24 volts to anything from 1.5 volts and up to the supply. I get the regulators at a local electronics distributor - I have included the Radio Shack and NTE cross referenced numbers.
Note: This is for DC voltage only. If I remember correctly, the basic circuit is printed on the back of the package at Radio Shack.