Hi Bob,
Thanks...please check your PM for my email address. I'll post this here in case anyone else is interested. Last night I was thinking about an opto isolator, but the only ones I have are limited to 1 or 1.5v. I have some Darlingtons I''ve used in alarm circuits 20 years ago. I have the 122 and the 127 plus the 5305. Thanks for mentioning those. I hadn't thought about them yet.
The circuit hasn't changed from before. I've been waiting to post it here, and I will once I know it works. I've tried tweaking certain aspects (resistor & capacitor values & relays, etc). First I set everything up on an old plug-in board, got it working (still have that temporary circuit here) and then built on a small (2 x 2) perfboard using the same size wire that's on the resistors, transistors, capacitor for connection. I've tested inside with a smooth power supply and on the vehicle. I've used 16 or 14 ga wire when testing on the vehicle and indoors alligator clip common patch cords.
Base-emitter saturation voltage is a min of .75 and max of 1.20 volts. Good point about the 3.3k resistor. That value was actually a stab in the dark and I've left it alone, but it might need to be a bit less. Yesterday I even dug out a box containing some old circuits I've saved to see if anything came to me...without success.
I don't have access to a scope. Not anymore, anyhow.
The relay came from a box of stuff I've saved since the early 70s. It is an NEC MR301-9ES. I don't think it has been made for a long time. All I know about it is that the contacts are suitable...rated at 5 amp at 16v and the wiper motor draws 2.6 amp on startup. It is NO/NC and the coil is around 250 ohm. This isn't one of the dual relays NEC sold back then, though. I've tried others. I've tried using a common reed relay to switch the Bosch type (and this works up to a point). It had been my hope to be able to use the Bosch type relays, however the problem is that they switch off too rapidly. This is to say they don't stay pulled in long enough and the low circuit doesn't move far enough or long enough to do anything but oooch the wiper blade forward a tiny bit at a time and without enough movement to kick the park function into play. The Bosch type relays have contacts rated to 30 amps at 14v dc, max switching power is 560W, the coil resistance is 70~80 ohm, coil operating current is 160ma, pulls in at 8v but drops out somewhere between 1.2 and around 5v.
Hope this is helpful.
