Waterproof??

[gughanath]

:-\I have made a case for my bike alarm out of ABS. I have drilled holes to allow sound from the buzzer to come out. Now, the problem is, if it rains, my alarm will get damaged because the water would flow through the holes into the circuit. The ABS is waterproof already, but how can I prevent the water going into the circuit without blocking the sound from the buzzer? ??? ???

[MP]

For a weatherproof container, the holes should be facing down. On the inside of the case, put a piece of cloth, thin padding, or other material that will allow sound through it. This should be placed (glued?) against the pvc where the holes come through. If the water gets in the holes, the material will "wick" the water away from the electronics due to the combination of the wicking action of the material and gravity. This will allow the moisture to exit.

MP

[gughanath]

hey. good idea but it is neccessary for em to have the holes on the front side of the case (the side that the user faces the alarm usually) due to aesthetics. Is there any other way to stop water rain destroying the electronics without having the holes behind the case?

[MP]

If the speaker /buzzer is waterproof, this helps. Then you only have to keep the circuit board dry. There are three options.
1. Conformal coating. You can dip your electronics in this solution and allow it to dry. After it is completely dry, you will have a sealed device. This will not work if you have an IC in a socket. The conformal coating will get between the pins and legs of the ICs and sockets and give you a poor connection.
2. Potting. This is done with an RTV which is made for use with electronics. Most RTV has chemicals which will corrode the components in electrical circuits. Again, the sockets will not work here. You can make a small form for your circuit, out the board in it, and fill it with the potting material. With this option, you must throw away the circuit if it ever needs repair. It would not be worth the time to dig down to the components.
3. Make a waterproof chamber in your case which keeps the electronics (circuit board only) dry. Then the abuse is only on the speaker or buzzer which makes the sound. You will still need a vent somewhere, otherwise it will sweat and you will have moisture in the chamber which will not get out. The vent should be on the bottom using the method I described earlier.

Hope these suggestions will help.

MP