Question for the electronics wizards (actuator driver)

[All_talk]

I need to drive an actuator (Ford power door lock) that requires a momentary polarity switching signal for open/closed. Trouble is, my signal source is a simple on/off. I have a electromechanically solution worked out using a DPDT relay to switch the polarity and limit switches to open the circuit at the actuator end points (I’ll post my sketch once I get a chance to scan it). The limit switch assembly will mount right on the body of the actuator and wouldn’t be too difficult to build, but I’m wondering if there might be an electronic solution.

I don’t really need the mechanical limits, a 1/2 second or so pulse would work fine. I was looking into a delay on circuit that would cut the power, but I’m not sure how to deal with the possibility of the source signal switching before the time out. It also seems that you could integrate the polarity switching as well. This sort of circuit design is just outside of my skill level (I’m a ME not an EE after all ), I’m sure I could figure it out, but I would have to spend quite a bit of time (re)educating myself.

Any of you electric smarties want to point me in the right direction?

Gary

[vrg3]

So you want a circuit that, when its input is triggered, will give you a half-second pulse on its output?

A 555 timer set up in a monostable (or "one-shot") configuration will do that easily. Just use the Goog.

It's probably easiest to just use the relays for polarity switching.

[All_talk]

I’ve done a little playin around with the 555 before working on a PWM circuit, that might be just the thing. I think I would need two “one-shot” timers, one to fire when the input goes high and one to fire when it goes low. Then split my polarity switching DPDT relay into two SPDT relays.

Here is the electromechanical circuit as it stands (sorry about the image quality, I didn’t have a scanner handy). The control has three modes, Open, Closed and Auto, the Auto mode is controlled by a normally open pressure switch. The default condition for the system is closed. The limit switches break the positive feed when the actuator hits the end point. The diodes complete the ground leg of the opposite function when the limit switch is open.



Gary

[All_talk]

I think I may have a solution…

An R/C delay on switch (see drawing) that will open the actuator circuit after the set time. I have drawn it out with a single delay circuit and relay, but in giving it a second look I may need two separate sides. I don’t think the cut out relay will reset in the short time that it takes the polarity switching relay to exchange contacts. Other wise I think it should work.





Comments?
Gary