Have you checked that your grounds are hooked up properly? This is the first thing that I am thinking of. If the ground is "rising" the apparent voltage can become less and less. Another option is the your 5V regulator does NOT like seeing the inductive load of the relay coil. If you remove the relay from the circuit (meaning just disconnect the coil) does it show the same behavior?Something is happening that is either a)taxing your main powersupply to draw that much current (in that case I would look at the relay hooked up wrong) or b) there is a weird grounding problem wih a rising voltage floor.
Hello Remmy,Let me give this a whirl. If i were going to design a circuit with the same power, input and output requirements, I would do the following:1. We will refer to the controlling attiny85 with the 4 outputs as the *controller*.2. I would lose the 4 channel attiny85's and replace them with a suitable transistor and associated cirtuitry to drive the base from the controller.3. I would lose the 2 zener diodes across the coil and just use a good diode across the relay coil to absorb the inductive kick.4. And finally, but not least, connect all 4 relay pin 1's directly to the +5 output of the 7805.I'm not an enginner. Just my thoughts. You might have to tweak my *thoughts* just a little.-oldfox-ps. Ohm's law works.