Build of 1973 Datsun 240Z 

   Home Electrical Defroster

Project just like most started as part of necessity rather then need. There are few reasons for changing the defroster switch, one of the main reasons was that the entire electrical system in the car was ripped out and replaced due to swapped out engine. I guess in part part of the system could had been left alone like lights and the defroster circuit but as the fuse block needed to be replaced plus the fact that the harness needed to be modified it was easier to just rip everything out and start fresh. Now since the fuse box was considerably larger and would not fit in the center console it needed to be placed in some other location. So the original place where the delay relay for defroster and couple other things where mounted on the right side where ripped out in favor of the new fuse box (see electrical for more details). So now comes the dilemma, not that the car would be driven in foggy spring or fall days and the fact that the original clock was also replaced by other meter and the fact that the defroster  switch, seat belt and choke lights are no longer functional its a good as any reason to have something else put in its place.
Originally a delay switch was wired from one of the GM cars for the defroster in place of the original switch but that was rather flimsy and with heavy wires it kind of started to fall apart and there still was the part of 2 non functioning lights. Hence the idea of multifunctional LCD display with couple switches to rotate through rotating screens came about.

The original idea was to just build a delay circuit or login in the code to turn defrost relay on and off and have 2 outputs to turn on driving/fog lights. That slowly started to expand to include following
 - defroster delay
 - driving/fog lights
 - clock
 - thermometer
 - seat belt warning as there is feed to the connector
 - voltmeter hence there is none in the car

A good place to locate all of the electronics is in the raised area of the flap.  A small 1.8" LCD is being utilized for the display function with 3 pushbuttons for controlling everything and one hidden for setup purposes. Face of the flap will be replaced with new piece of black plastic with cut out for the display and holes for buttons. Back side is enclosed thus protecting the circuit board


Hardware revisions
Prototype: No revision markings on PCB original version after prototype

Rev 1.01: re-routed couple traces to R1 and R2 moved DHT added R15, D8 & D9 connected to PD5 on CPU for seat belt warning light


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