Hi Jon G.
Very cool idea. I like your circuit design.
As you probably already know, the wiper switch sequence on most production GM vehicles with the delayed wiper feature goes from off, to max delay to min delay, to lo speed, then high speed. And yes, like many other features, wiper function on new vehicles is typically up-integrated into some type of body control module. This provides for better control, more flexibility in switch design (switch is now just a low current input), expanded features like wipe for n number of wipes whenever the washer is activated, and easier integration of automatic controls such as rain sense or headlight activation whenever wipers are on.
With regards to wiper park, the vehicles you are designing for may be different, but the GM wiper motors that I am familiar with typically have 12 volt ignition going to the motor, with the wiper switch controlling the ground path to either the low speed or high speed motor windings. The motor typically contains some type of cam and switch arrangement, which provides an internal ground to the low speed motor winding until the wiper arms reach the park position. There are those on this forum that know these circuits well, so I'm sure they will correct me if this is in error.
Hopefully I'm wrong, so you won't have to modify your circuit - as it controls through the high side.
Speaking of which, if it does drive thru the high side, will that 10K resistor in series with the rotary switch cause an issue ?
Also, I confess that I'm trying to figure out how the rest of the circuit works. I get the part about the NPN transistor energizing the relay. I also (I think) understand that you are changing the RC time constant of the circuit made up by the cap and whichever resistor is selected from the switch. I see that you have the negative plate of the cap connected to the emitter of the NPN. Is that to discharge it whenever the relay is energized? Also, is it possible that the collector and base labels on the PNP transistor are reversed? I'm thinking that the maybe RC should be attached to the base?
Sorry if these sound like ignorant questions. The last analog circuits class I had was in like 1986.
Best Regards...
p.s. I've seen a lot of these circuits designed with 555 timers. Would that be an option, too ?
p.p.s. My truck has vacuum wipers also, so when you come up with a design to add the delay feature to those, let me know...
