Where to buy ? Filters, Voltage Protection & TTL Converters

Development Boards Arduino
1

Suggestion Required to buy these 3 things with readily available stuff ?

  1. Filters for 0 – 5V signal and over voltage protection for the analog signal for arduino.

  2. Dual Power supply with reverse voltage protection 1Amp both 3.3V and 5V.

  3. RS232 circuit TTL converter.

thx everyone…

Dr.Moobi