Aluminum enclosure and ESD protection

[vsaar]

Hi,

Last night I zapped my self-made alarm clock with a good dose of ESD, after removing my shirt and then touching the aluminum case with my finger. The 7-segment display froze and showed some random characters, and after restarting it I noticed one segment being dead on every number. I fixed it by replacing two 74HC595 shift registers in it. The other ICs, including the AVR seemed to survive from the zap.

Some pictures here: **broken link removed**
**broken link removed**
Currently that aluminum case is not connected to anything, obviously leaving the clock vulnerable to ESD damage. The power comes from an SMPS type 12V wall-wart (originally from a WD external hard drive). Should I just connect the case into the circuit ground for ESD protection, or are there something else which would make that a bad idea?

 

[MikeMl]

Do you have a third wire (earth ground) in your outlets in Finland?

Is the wall-wart inside the aluminum case, or separate from it?

Are there only two wires from the wall-wart to the clock? Could there be three?

 

[vsaar]

Do you have a third wire (earth ground) in your outlets in Finland?

Is the wall-wart inside the aluminum case, or separate from it?

Are there only two wires from the wall-wart to the clock? Could there be three?

Yes, I have 3-wire Schuko outlets. However the wall-wart is separate and has only two-wire cord with Europlug, so can't use real earthing for this.

 

[MikeMl]

I have built similar projects, and what I did was enclose the Wall-Wart (guts) inside the metallic case, and then used a three-wire line cord where the ground-wire is connected to the case. This will still not completely solve the zap problem you encountered, only minimize it. There is a much higher probability that when touching the clock, you touch the case first, and thereby discharging yourself before touching the button...

Every time you touch the clock, it will remind you to touch the case first, too...

 

[chemelec]

I would just Ground the Aluminum Case.