Hello
could somebody look at the circuit diagram attached

the problem i am having is intermittently the Atmega chip resets ...
this only happens when the relays are d energised supplying the two solonoid valves

i think that maybe its a voltage spike ... i do have the circuit protected by flyback diodes(1N4004)

5volts to the relay ...........12volts to the valves

any ideas

thanks

 

I assume both -ve sides of each supply are common?
If so make sure there is a direct return path for the 12v common.

These spikes are the worst.!
Max.

 

are you sure that is your schematic? i cant find 12 volts anywhere on it. Your relay will do nothing the way it is drawn. you cannot feed a 7805 with 5 volts and get 5 volts out. i found more problems but dont want to try typing that much with this phone. perhaps you posted an older working diagram, do you have other files that are more in line with your described circuit?

suggest a seperate 5 volt supply that is dedicated to your micro and not connected to any relay.

 

What current are the Solenoids, you may be able to drive them with a Mosfet instead of a relay?
Max.

 

Standard beginner problem. The cure is not in the schematic, it is in the physical world. Make dedicated wires for each relay, add bypass capacitors to your processor chip, isolate your power sections with things like a diode and a capacitor or a 100 ohm resistor and a capacitor, etc. Glitch happens. Learn how to redirect or absorb the energy in safe ways.

 

BTW as well as the relays, you also need a 1N4004 across the solenoids, which could well be the problem!.
Max.

 

BTW as well as the relays, you also need a 1N4004 across the solenoids!

Caught me assuming again. A relay coil is the same as a solenoid (in my mind) so I did not differentiate for the TS.

 

As i have already had some Pcbs made .... because i have only just spotted this problem
do you thing decoupling cap would be a good start point because i can add these to the board....

 

Decoupling is important as well as the BEMF diodes mentioned.
Did you design for diodes across the solenoids, these are normally at the coil rather than the board, anyway.
Max.

 

You only have 3 choices: Try some band-aids, learn and do all the math, redesign the board.
Pick one.

 

hi yes the Solenoids have diodes.
but i can see now that decoupling is needed on the atmega
do you think a voltage drop could be resetting the atmega would the decoupling help with this?

this is my first ever electronic project so don't really know what i am doing

the diodes are on the board

 

Optimally, Move the diodes.
Voltage drop, sagging glitch, ground plane bump...no difference to a capacitor across the processor.

It all ends up at, "exactly where in the physical world is that current causing a glitch?".

 

You can help isolate the micro with a capacitor directly across the power pin to the common pin, and a series resistor a ferrite bead in series with the power line from the micro (and only the micro) to the supply.

 

Good. Another, physically tiny, isolation method from crutschow.