I´ve been given a control board from a spa. Basically it does 2 things, first checks that the water level is high enough in the spa and second, starts and stops the pump from a water proof push button. The push button and water level sensors are broke. I got a new sensor and made a new board and the spa is working again. However, now i´ve got the old board I´m currious how it actually works. I´ve drawn a schematic from the board (see below) and I understand everything except what the point of resistors R1, R2, R3, R7 is and why R4 is such a high value. They seem to me to configured as voltage dividers, but why?
![](http://img100.imageshack.us/img100/9220/spa.th.png)
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ImageShack.usPL1 = Mains in (230v)
PL2 - Supply for pumps (230v)
PL3 = Water Sensor (optical I think)
PL4 = Push Button to start/stop
I have never dealt with PIC´s before, but the idea seems to be much the same as the Atmega chips, which I have dealt with. So i get how the inputs and outputs works, infact that part of the circuit is the same as the one I built. I just don´t understand the resistors.
Any help wouyld be appreciated.
Many Thanks