Friday afternoon. Bavaria panel, reporting black tank full all the time...
555 generates a square wave signal which then goes on tanks connections, in the middle we have signal diodes, pulldown resistors, transistor and few capacitors... This boards is a pain to work on. Most of the times it corrodes and you can,t reach other side, 90% of all traces go between layers and it is got protective coating which is real pain to remove... tracing the signal i took away few of components to inspect them and they were all good. The problem was in cold solder joint on one of the capacitors, signal looked very disorted on the other side and microcontroller thought that tank is reporting full... Sensors are basically on/off swithes, they connect signal to ground.
