Intermittent windscreen wipers...

[Mad Mart]

Graham, this is the circuit I used...

https://www.youtube.com/watch?v=zgiAbTIupBk

I had it attached to the wiper circuit but it was something in the way the Dolly wiper circuit works that I couldn't get it to work properly. It was to do with the wiper parking circuit.

[marko]

Vehicle wiring products do a 5 second intermittent relay. 0115 9305454 or www.vehicleproducts.co.UK code glr8

[GrahamFountain]

Graham, this is the circuit I used...

https://www.youtube.com/watch?v=zgiAbTIupBk

I had it attached to the wiper circuit but it was something in the way the Dolly wiper circuit works that I couldn't get it to work properly. It was to do with the wiper parking circuit.

I have to admit that I'm a bit rusty when it comes to discrete transistors. I haven't tried to analyse the circuit, but I assume it's based on an astable multi-vibrator with a variable space and fixed mark duration.

I suspect the problem is that the pulse to the relay isn't long enough to unpark the wipers. But if it's long enough to nudge the system towards being unparked, it should still wipe every so often.

It should be possible to change the pulse length by changing the R-C circuit that sets it, but then you'd probably have to change the one that control the interval between pulses as well.

It might be fun to try to lengthen the pulse, if you've got a big box of different cap and resistor values, one of the development boards like he's using in the vid, a spare wiper motor, and a 12v supply (and maybe a digital oscilloscope to see the pulse lengths, etc.). But all I have is the development board (I think) and the scope.

The other problem I'd see with this, and many of the other add-in circuits, is that you either need an extra switch or a potentiometer, so that you can cover the normal wipe function as well as intermittent; whereas, the BL solution uses the switches that are already there. It's not, as I said, perfect, as it only gives one intermittent wipe speed. But it is just a straight splice into the wiring loom with no visible modifications to the car.

To do that with one of these add in circuits would need a little logic to control the power supply to it, which should do the following:

• When the intermittent circuit is initially off, a short pulse of current from the wiper control switch, which doesn't have to be long enough to unpark the wipers on its own, causes the power supply to the circuit to latch on, so the wipers wipe intermittently forever (or until it's all reset by turning off the ignition, etc.).
  
  A longer pulse from the wiper control switch, which should be something longer than the time to unpark the wipers, doesn't latch the supply to the circuit when the wiper control switch is let go of, so the switch in the wiper motor will just finish the wipe it's doing at that time, and you get the normal one wipe function.
  
  When the intermittent circuit is already on, a short pulse from the wiper control switch causes the power supply to the circuit to unlatch, removing the supply from the circuit so it stops wiping intermittently.

Then you just hook the combined circuits in between the wiper control and the motor, and supply from the ignition switch.

The question is, whether it's easier and or cheeper to add that logic to one of these circuits, or get one of the BL units that already contains both.

[Mad Mart]

It was a few months ago when I tried the circuit but I remember it pulsed the wipers on ok but then the wipers would stop wherever they were when the feed was cut, i.e. they didn't park. I'm wondering if I need to include a second relay.

[tinweevil]

Mart, look in your loose leaf manual at 84.15.00 sheet 2. Normally when parking the circuit takes power from the motor N/LG through the sweep switch and main switch 0 position back to the motor in R/LG. When the switch is is position 1 the park circuit is broken. At a guess you're only using the NO contact on your relay? You need to use NC as well and wire the relay in parallel with the sweep switch.

[Mad Mart]

Eureka! Never thought of that Julian. I think you may have solved my problem.